five pairs of once-branched appendages on thorax; abdomen
without appendages; abundant in fresh and salt water; many
forms parasitic/)
^Cyclops^
^Cetochilus^
^Sapphirina^
^Siphonostomata^
^Nicothoë^
Order =CIRRIPEDIA= (/Imperfectly segmented; fixed or
parasitic during adult life; inclosed in skin strengthened
by calcareous plates; abdomen rudimentary; appendages
biramous, usually six pairs/)
Genera Species
^Lepas^ ^L. anatifera^
^L. striata^
^L. pectinata^
^Balanus^ ^B. balanoides^
^B. eburneus^
^B. rugosus^
^B. geniculatus^
^B. tintinnabulum^
Suborder ~RHIZOCEPHALA~ (/Parasitic/.)
^Sacculina^ (parasitic on crabs)
^Peltogaster^ (parasitic on hermit-crabs)
Subclass =Malacostraca= (/Highly organized Crustacea, usually
of considerable size; appendages much differentiated/)
Order =PHYLLOCARIDA= (/Small; covered with bivalved carapace;
thoracic feet leaf-like; abdominal feet biramous; posterior
segment terminates in two long spines; mostly fresh-water
species/)
Order =SCHIZOPODA= (/Small; transparent; shrimp-like; thorax
more or less completely covered with soft carapace;
thoracic appendages biramous; eyes on stalks/. /Mysis/ are
/Without gills or thoracic legs/; /Euphausia/ are /With
gills or thoracic legs/.)
^Mysis^ ^M. sternolepis^
^Euphausia^
Order =DECAPODA= (/Thoracic segments unite with head and form
cephalothorax, which is covered by carapace; eyes stalked;
maxillipeds have exopodites; five pairs of walking-feet
without exopodites/)
Suborder ~MACRURA~ (/Abdomen usually longer than
cephalothorax and commonly extended; rostrum usually
prominent; eyes not inclosed in orbits; antennæ and
antennules large; antennæ have exopodites/)
Set Free-swimming Forms: Shrimps and Prawns
^Penæus^ ^P. setiferus^
^P. brasiliensis^
^Palæmonetes^ ^P. vulgaris^
^Crangon^ ^C. vulgaris^
^C. franciscorum^
Families Genera Species
Set Creeping Forms: Lobsters and Crawfish
ASTACOIDÆ ^Homarus^ ^H. americanus^
^Panulirus^ ^P. interruptus^
^P. argus^
^Scyllarus^
Set Anomalous Forms: Approaching the Brachyura
Suborder ~ANOMURA~ (Of these Families, the Lithodidæ have
/Fifth pair of feet folded under the carapace/)
DROMIDÆ ^Hippoconcha^ ^H. arcuata^
PAGURIDÆ ^Pagurus^ ^P. bernhardus^
^P. pollicaris^
^P. longicarpus^
^Clibanarius^ ^C. vittatus^
^Pylopagurus^
CENOBITIDÆ ^Cenobita^ ^C. diogenes^
HIPPIDÆ ^Hippa^ ^H. talpoida^
^H. analoga^
^Albunæa^ ^A. gibbesii^
PORCELLANIDÆ ^Porcellana^ ^P. sayana^
^P. sexspinosus^
^Petrolisthes^ ^P. armatus^
LITHODIDÆ ^Lithodes^ ^L. maia^
^Echidnocerus^ ^E. cibarius^
^E. foriminatus^
^Acantholithodes^ ^A. hispidus^
^Cryptolithodes^ ^C. sitchensis^
^Phyllolithodes^ ^P. papillosus^
Suborder =BRACHYURA= (/Abdomen shorter than cephalothorax,
and permanently folded under it; eyes inclosed in orbits;
antennules and antennæ small/. Of these Families, the
PORTUNIDÆ are called /Swimming crabs/; the OCYPODIDÆ are
called /Sand- and fiddler-crabs/; and the MAIIDÆ are the
so-called /Spider-crabs/.)
Families Genera Species
PORTUNIDÆ ^Carcinides^ ^C. mænas^
^Callinectes^ ^C. sapidus^
^Ovalipes^ ^O. ocellatus^
Set WALKING CRABS
CANCROIDÆ ^Cancer^ ^C. irroratus^
^C. borealis^
^C. magister^
^C. productus^
^C. antennarius^
^Menippe^ ^M. mercenaria^
^Eupanopeus^ ^E. herbstii^
^Eurypanopeus^ ^E. depressus^
^Neopanopeus^ ^N. texana^
^Rhithropanopeus^ ^R. harrisii^
GRAPSIDÆ ^Hemigrapsus^ ^H. nudus^
^H. oregonensis^
^Pacygrapsus^ ^P. crassipes^
OCYPODIDÆ ^Ocypoda^ ^O. arenaria^
^Uca^ ^U. minax^
^U. pugnax^
^U. pugilator^
MAIIDÆ ^Libinia^ ^L. dubia^
^L. emarginata^
^Hyas^ ^H. coarctatus^
^H. lyratus^
^H. araneus^
^Loxorhynchus^ ^L. crispatus^
^Pugettia^ ^P. gracilis^
^Sternorhynchus^ ^S. sagittarius^
^Epialtus^ ^E. productus^
^Pitho^ ^P. aculeata^
^Lambrus^ ^L. pourtalesii^
CALAPPIDÆ ^Calappa^ ^C. flamma^
PINNOTHERIIDÆ ^Pinnotheres^ ^P. ostreum^
Order =STOMATOPODA= (/Abdomen very large; second pair
of thoracic legs very large; gills borne on abdominal
segments/)
^Squilla^ ^S. empusa^
Order =CUMACEA= (/Small, shrimp-like/)
^Diastylis^ ^D. quadrispinosus^
Order =ARTHROSTRACA= (/No carapace, as a rule; six to seven
pairs of walking-legs; eyes sessile/)
Suborder ~AMPHIPODA~ (/Body usually compressed laterally/)
^Orchestia^ ^O. agilis^
^Talorchestia^ ^T. longicornis^
^Gammarus^ ^G. locusta^
^Chelura^ ^C. terebrans^
^Caprella^ ^C. geometrica^
Suborder ~ISOPODA~ (/Body depressed or flattened/)
^Cirolana^ ^C. concharum^
^Limnoria^ ^L. lignorum^
^Sphæroma^ ^S. quadridentatum^
^Idotea^ ^I. marina^
^I. ochotensis^
^I. metallica^
^I. wosnesenskii^
^Chiridotea^ ^C. cæca^
^C. entomon^
Class =MERISTOMES=
Order =XIPHOSURA=
^Limulus^ ^L. polyphemus^
Class =PANTOPODA= (Lang)
Order =PYCNOGONIDA=
^Phoxichilidium^ ^P. maxillare^
[pg243]
TERMS USED IN DESCRIBING CRUSTACEA
^Abdomen^: The posterior part of the body.
^Antennæ^: Articulated appendages which immediately precede the mouth.
^Anten´nules^: The anterior of the two pairs of feelers of the head.
^Bira´mous^: Having two branches.
^Carapace^: A thin chitinous shell covering the cephalothorax.
^Cephalic^: Pertaining to the head.
^Cephalotho´rax^: The united head and thorax.
^Chela^: The pair of pincers, or claw, which terminates some of the
appendages.
^Che´liped^: A leg with chela, or claw, at the end.
^Endop´odite^: The inner one of the two main divisions of the limb.
^Epime´ra^: Divisions on the ends of the segments of amphipods and
isopods, and belonging to the legs.
^Epip´odite^: A third branch of a limb.
^Epis´toma^: A triangular area in front of the mouth.
^Exop´odite^: The outer one of the two main branches into which the
typical limb of any segment is divided.
^Gastric mill^: The first half of the stomach, where food is ground.
^Mandibles^: The pair of appendages next behind the antennæ.
^Maxil´læ^: The first pair of appendages after the mandibles.
^Maxillipeds^: The three pairs of appendages after the maxillæ.
^Metame´res^: Segments.
^Orbits^: Eye-cavities, peculiar to the higher /Crustacea/.
^Prosto´mium^: The region in front of the mouth; the preoral part of
the head.
^Rostrum^: The beak in front of the head.
^Segment^: A part cut off or marked as separate from others.
^Somite^: A segment of the body.
^Squame^: A scale.
^Telson^: The last segment of the abdomen.
^Thorax^: The middle part of the body.
[pg244]
ARTHROPODA
This subdivision of the animal kingdom includes insects, centipedes,
spiders, and crustaceans, which together constitute more than
half the known species of animals. Although these animals are so
unlike in general appearance, it is easy to recognize the common
characteristics which place them together in one group. The name
/Arthropoda/, meaning "jointed-footed," suggests perhaps one of the
most obvious points of resemblance. The /Arthropoda/ have bilateral
symmetry, one side of the body being like the other; they are covered
with a horn-like material (chitin); they are divided into segments;
the segments have appendages; and the appendages are jointed so as
to admit freedom of motion. Their manner of growth is peculiar; they
cast off their rigid external coverings and secrete larger coats of
mail, and at these periods increase in size or undergo metamorphosis.
There are such modifications of these general features as the habits
of the different species demand. For instance, the appendages may be
constructed for walking, swimming, boring, sucking, or the seizure
and preparation of food. In some animals the appendages form a part
of the breathing-organs, in others are used as organs of sense. Every
detail of the organism, down to the hairs, has its special use and
function.
CLASS =CRUSTACEA=
The crustaceans vary in size from microscopic minuteness to two feet
or more in length. The giant crab of Japan (/Kaempferia kaempferi/)
exceeds this, being commonly from eight to twelve feet [pg245]
across the arms, and is said to reach even greater proportions.
Crustaceans live on land and sea, and in both fresh and salt water;
they may be parasitic, sedentary, or free and active. There are said
to be over ten thousand species, which include crabs, lobsters,
shrimps, beach-fleas, wood-lice, barnacles, and water-fleas. Nine
tenths of the species are marine; of these some are pelagic, and
their transparent forms constitute a part of the plankton. Others
live on the bottom in deep water and attain a large size. A vast
number live in the littoral zone and form a considerable part of that
crowded community. They are scavengers and freebooters, being great
fighters, as well as predatory in their habits. As a rule, they feed
on dead organic matter, which they consume in surprising quantities;
some have also a vegetarian diet. They have, like starfishes, the
singular power of throwing off their limbs and growing new ones.
The /Crustacea/ derive their name from the nature of their crust or
covering. This is earthy and brittle, not stony, like the shells
of mollusks. This crust, or exoskeleton, has various degrees of
firmness, from that of a delicate polished cuticle, seen in small
forms, to the heavy armor of some crabs and the shell-like character
of the covering of barnacles.
The lobster and crab are perhaps the most comprehensive examples as
well as the largest in size of the class, the vast majority of the
species being minute forms. The ocean swarms with varieties too small
to be noticeable to the naked eye.
It is the province of /Crustacea/ to consume decaying organic matter,
both animal and vegetable, and in doing this they perform a great
service in purifying the waters of the pool, the shore, and even the
sea. Not only in this are they serviceable, but to a great extent
they serve as food for other animals, their flesh being palatable
and preferred to that of other animals whose diet would seem to make
them more wholesome. The small forms exist in such myriads, and
increase so rapidly, that, although extremely small, they furnish an
inexhaustible supply of food. Even some whales subsist upon these
minute animals, and for man the larger species are articles of diet
that are counted among the luxuries. The crustaceans are remarkable
for their varied forms and for their [pg246] perfect adaptation to
many different conditions of life. There is no class in the animal
kingdom which presents so wide a range of organization, or whose
structure deviates so widely from the type form. These differences
lie chiefly in the external characters and in the structure of the
appendages.
Some species are solitary, like lobsters and crabs; others, like
shrimps, are gregarious and live in immense shoals. In the habits of
these animals there is much which excites wonder and interest.
ANATOMY OF THE HIGHER CRUSTACEA
The body of a crustacean is divided into segments, which are
sometimes distinctly separated, like joints, and sometimes fused
into one piece. The head part is called the /cephalic/ portion,
the middle section is the /thorax/, and the posterior part is the
/abdomen/. The horn-like covering of the thorax is the /carapace/;
where it projects over the head it is the /rostrum/. When the head
and thorax are united, as in most /Crustacea/, the anterior or front
portion of the animal is called the /cephalothorax/. Each segment
has a pair of appendages. Each appendage has a joint attached to the
body; from this arise two jointed branches, the /endopodite/ and
the /exopodite/, the inner and the outer foot. The appendages are
modified to perform special functions. In front of the mouth are two
pairs: the smaller ones are the /antennules/ and have ears at the
base; the larger ones are /antennæ/ and are feelers. At the base of
the antennæ are the /green glands/, said to have renal functions.
Both the antennules and the antennæ are fringed with hairs, which aid
in the sense of touch and perhaps of smell. On each side of the mouth
are the /mandibles/. Then come the /maxillæ/ and the /maxillipeds/,
used in capturing and tearing the food and conveying it to the mouth.
Thus it will be seen that some of the appendages around the head
are connected with the senses, and others are used in eating. Those
of the thorax are for walking; those of the abdomen for swimming,
guarding the eggs, etc. The food taken into the mouth passes into
the stomach through a short passage. The stomach is divided into two
parts. The front [pg247] one contains three long teeth which meet
laterally and grind the food; this is known as the /gastric mill/.
When sufficiently fine, the food passes through a strainer of stiff
bristles into the smaller portion of the stomach, where it is
partially digested, and from there enters a long, straight intestine
which reaches the length of the body and opens to the outside on
the under side of the /telson/, or last segment. A large liver also
pours its secretions into the intestine. The green substance commonly
called "fat" in lobsters is the liver.
The heart consists of an elongated tube, or a short sac, which lies
directly under the integument of the back. From this heart-sac,
blood, which is colorless, is sent by arteries to all parts of the
body; it then collects in spaces called /venous sinuses/, from which
it goes to the gills, and thence back to the heart.
The nervous system begins in a large ganglion in front of the mouth,
called the brain; from this two branches arise, which pass on each
side of the digestive organs, meeting in ganglia in each segment
and extending the whole length of the body. The gills, by which the
animal breathes, are upon the limbs, or on the walls of the body
immediately adjacent to them, and are generally inclosed in special
chambers. In lobsters and crabs two such chambers are found under
the flaps of the carapace, above the walking-legs. Gills are divided
so as to present much surface to the water, from which they absorb
oxygen. They are like a dense mass of little tubes arranged along a
central tube. The class has two kinds of eyes, simple and compound;
the latter are composed of a number of eyes. In some species the eyes
are placed on the ends of movable stalks, which enable the creature
to see in all directions and from a higher plane than the body
occupies. As a rule, the eyes occur in the head region, but in the
shrimp /Euphausia/ they are on the thorax and abdomen. In barnacles
simple eyes exist in the young stage, but in adult forms there are
no apparent visual organs. The ear (so called) consists of a sac
containing small silicious particles suspended in fluid. Numerous
fine hairs on the inner surface of the sac connect with nerve-fibrils.
The organs of hearing are in various places. In decapods, or the
larger /Crustacea/, they are at the base of the antennules. [pg248]
The muscles are white bundles of fibers, and are in strips, which is
an indication of power and activity. There are four important sets:
twisted ventral muscles which bend the tail and are particularly
large and strong, those which straighten the tail, those moving the
appendages, and those which work the gastric mill.
[Illustration: Zoëa of /Cancer irroratus/. Last stage before it
changes to the megalops condition.]
The eggs, after being discharged, are attached to the abdominal legs
of the mother by a kind of cement, or they are carried in pouches
attached to the thorax. In these positions they mature, and hatch at
different stages of development in different species. Some emerge
with three pairs of legs, and are known as /Nauplius/; some are
/Zoëa/, having a carapace and abdominal segments, but no abdominal
appendages. Another stage is /Megalops/, with large stalked eyes.
Others are hatched as miniature adults. These names were given when
the embryo stage was not recognized and the larvæ were thought to be
distinct species.
[Illustration: Megalops stage of /Cancer irroratus/, just after
change from zoëa stage.]
The growth of the animal is effected by moulting. The /Crustacea/
are named from the crust-like covering which envelops them. It is
a horny material, called chitin, in which are deposited particles
of carbonate of lime, making a rigid envelop which would prevent
all freedom of motion, were it not that there are spaces free from
lime, and thus flexible joints are left. When the animal expands it
throws off this hard covering and secretes a new and larger one. As
the time of moulting approaches, the old covering becomes loosened,
and a delicate new one is formed beneath it. The old shell splits
open across the back just behind the carapace, and the soft animal
withdraws first its cephalothorax and then its abdomen, leaving the
cover complete, including even the covering of the eyes and the
lining of the stomach. The [pg249] new shell is rapidly hardened,
being already formed when the old one is cast, and the animal
regains its normal condition in about a week; in the meantime it
is defenseless, and lies quiet in some secluded place. Moulting is
an exhausting process, and is attended with great dangers. A great
mortality occurs at this time from accidents, from weakness, and also
from helplessness in case of attack.
The hair-like processes scattered over the shell, often like fringes,
are said to be organs of feeling.
SUBCLASS =ENTOMOSTRACA=
These are /Crustacea/ of small, often microscopic size, of
comparatively simple organization, and with appendages adapted
to serve the purpose of respiration. These minute animals may be
obtained by skimming the surface of the water with a muslin net,
preferably at night, then washing off the inside of the net with a
small quantity of water into a glass dish. Place the dish on a dark
surface before a light, and the little creatures will gather toward
the light, and may be satisfactorily observed with a glass.
ORDER =COPEPODA=
This order, though composed of minute forms, is one of great economic
importance, from the fact that the little crustaceans exist in
vast numbers and furnish a very considerable part of the food of
many fishes. ^Cyclops^ is the most common of the fresh-water, and
^Cetochilus^ of the marine genera. These, together with other genera,
swarm in water wherever life exists, from the smallest pools and
ditches to the broad surface of the ocean. Without having drawn
a surface-net on some sheltered bay, it is difficult to have an
idea of the myriads of /Entomostraca/ in the sea. Although nearly
transparent and of such delicate texture as to be almost jelly-like,
they sometimes color the sea with a reddish tint for miles. Whales
which have baleen, or fringes of whalebone, in the mouth subsist
on these small organisms, which are called "brit" by the whalemen.
The whales, sometimes in schools, rush through the water with open
mouths, engulfing these little [pg250] crustaceans, the baleen
straining them from the water. Although devoured in such immense
quantities, and sometimes lying dead in sheets of scum on the surface
of the water, they maintain their numbers by the exceeding rapidity
with which they reproduce. It has been computed that the descendants
of one /Cyclops/ may number in one year 4,500,000,000, provided all
the young reach maturity and produce a full number of offspring.
One of the free marine forms, ^Sapphirina^, is of especial interest,
as it surpasses all animals in phosphorescence and sparkles by day as
well as by night. It is one quarter of an inch long, and is broad and
flat.
Besides the myriads of free-swimming copepods, there are parasitic
forms in great number. The marine parasitic forms are commonly known
as fish-lice. They have various habits, some living as commensals,
others attaching themselves to animals only to be carried about; the
true parasites live upon the blood and tissues of their hosts, and
may fasten themselves to the external parts of the body or to the
internal organs. Whales, fishes of all kinds, mollusks, starfishes,
jellyfishes, and corals, all have some form of parasite, and many
have several different kinds of guests. It is said that the haddock
has more than a dozen which infest its external and internal
membranes.
^Nicothoë^ is found on the gills of lobsters. The truly parasitic
forms are usually very degenerate and lose the characteristics of
their order.
ORDER =CIRRIPEDIA=
("/Curled feet/")
THE BARNACLES
Barnacles of the genus /Balanus/ (acorn-shells) (Plate LIX.) are
familiar objects on rocky shores, which they often whiten with their
shells, and those of the genus /Lepas/ are also widely known. The
name of the order is descriptive of their curled appendages. The
appendages are fringed like feathers and are drawn into or protruded
from the shell at will. When extended they are constantly in motion,
and create currents which carry food to the [pg251] mouth of the
animal, which is dependent upon such food as comes within range of
its tentacles.
[Illustration: /Balanus./ A, external view: /s/, scutum; /t/, tergum.]
[Illustration: /Balanus./ B, anatomy: /a/, antennules; /ad/, adductor
muscle; /m/, muscles of scuta and terga; /o/, edge of parapet; /ov/,
ovary; /ovi/, oviduct; /sc/, scutum; /sk/, parapet; /t/, tergum;
/wo/, female aperture.]
Their life-history is interesting. The young barnacle, called a
/nauplius/, in no way resembles the adult. When it emerges from the
egg it is a free and independent animal, with one eye, three pairs
of legs, and a single shell. It swims about for a while and moults
several times. It then has two eyes, two shells, and six pairs of
legs. At this period it seeks a permanent home, and attaches its
anterior end to the object it selects by means of its antennæ,
which have become suckers. It makes its hold secure by secreting a
cement which permanently fastens it to the spot. It then undergoes
metamorphosis, loses its bivalve shell and its eyes, and attains its
characteristic /cirripeds/, or curled feathery legs, and a new shell
covering. During these transformations, from the time it becomes
fixed until it attains its adult form, the barnacle fasts, living by
the absorption of its own animal fat. Its food subsequently consists
of the minute animal forms which abound in the sea. Its further
growth is by moulting, but parts only of its covering are disengaged;
the shell is permanent, and its successive stages of growth are
marked upon it by lines, as in mollusks. The lining of the shell, or
enveloping skin of the animal, and also the cuticle of the legs are
[pg252] shed, and in the spring of the year these thin, glossy casts
are found in abundance floating on the surface of the water near the
shore.
There are but three orders of barnacles, namely, those in which the
shell is directly attached to the rocks, those which are attached to
floating objects by a long stalk, and those which are parasitic on
animals. A species of the third order infests the whale.
The older zoölogists classed barnacles with the /Mollusca/, but in
1829 Vaughan Thompson, in the study of their embryology, found that
they should be classed with crustaceans, in company with crabs,
shrimps, and water-fleas, with which their immature forms show direct
relationship.
GENUS ^Lepas^
This genus is commonly known as the ship-barnacle, also as the
goose-barnacle. It attaches itself to floating logs as well as to
ships, but the latter form its principal home; consequently it
is a great voyager, and, though common everywhere, is everywhere
considered a stranger. The same species are found on ships coming
from the most remote and widely separated regions, and so they cannot
be considered native to any one locality. They are wanderers on the
deep, and grow in such numbers on the bottoms of ships, especially
of those which sail in warm seas, that they seriously impede the
progress of the vessels. Aside from diminishing its speed, they do a
ship no injury.
There was a tradition, which lasted several centuries, that geese
were hatched from these shells, which somewhat resemble eggs. Gerard,
in the appendix to his "Herball or Generale Historie of Plants"
(1597), gives a picture of shells of /Lepas/ growing on a tree, with
geese falling from them and swimming about in the water below. His
description is as follows: "There are founde in the North parts of
Scotland and the islands adjacent called Orchades certaine trees
whereon do growe certaine shell fishes of a white color, tending to
russet, wherein are conteined little living creatures; which shells
in time of maturitie do open, and out of them grow those little
living foules whom we call barnakles, in the North of England brant
geise, and in Lancashire tree geise; but [pg253] the other that do
fall upon the land do perish and come to nothing." He then describes
in detail the various transformations, and ends with: "But what our
eies have seen and hands have touched we shall declare."
The long, flexible stalk of /Lepas/ is its anterior end. Generally
this stalk is only half an inch long, but in some species it attains
the length of a foot.
Huxley describes the barnacle as a crustacean fixed by its head and
kicking food into its mouth with its legs. The mouth has a pair of
small mandibles and two pairs of maxillæ, the last pair uniting to
form a lower lip. The thorax has six pairs of branched appendages.
The body is enveloped in a fold of skin, to which are attached five
shell-like plates. One of these plates is long and narrow, and
extends along the dorsal side; two are large and triangular (the
terga); two are small and triangular (the scuta), the long point
extending downward. These shells are on the free or posterior end.
Barnacles have a nervous system, consisting of a brain and a chain
of five or more ganglia, but no special respiratory or circulatory
organs are known; the cirripeds, or feet, are supposed to perform
these functions. They have also a food-canal, a digestive gland, and
excretory tubes. The eggs are carried under the external fold of the
skin in flat cakes.
^L. anatifera.^ The shell is bluish-white, showing lines of growth
and faint radiating lines emanating from the anterior basal angle.
The upper valves are narrow; the long tips point downward, and
the top is blunted, leaving a space which is occupied only by a
membrane. Near the apex of the shell, at the back, is a distinct
angle. The dorsal valve is broad, not much compressed, and is
sometimes grooved lengthwise. The cartilage of the shell and
the stalk adjoining the shell are orange-colored. The stalk is
grayish-brown and the cirri flesh-colored. The stalk is from one
inch to six inches long. The shell is one inch long.
^L. striata.^ Shells bluish-white; valves sharply triangular;
dorsal valve compressed, forming a ridge; lines radiate from the
basal angle of the lower valves and from the upper angle of the
terminal valves, starting from the extreme end; the margins have a
narrow edge of yellow cartilage; the stalk and cirri are of a dark
slate-color; shell and stalk are each about an inch long.
^L. pectinata.^ Shell shorter and less compressed than in the
preceding species; lines of growth and radiating lines distinct; a
decided line [pg254] runs from anterior base to summit, a little
back of the margin; terminal end broadly obtuse (truncated); dorsal
valve much compressed, forming a sharp edge serrated with ten to
twelve teeth and distinctly striated or furrowed.
[Illustration: /Lepas anatifera./ A, the entire animal; B, anatomy.
/a/, antennule; /c/, carina; /cd/, cement-gland; /l/, digestive
gland; /m/, adductor muscle; /od/, oviduct; /ov/, ovary; /p/,
peduncle; /s/, scutum; /t/, tergum and testis; /vd/, vas deferens;
/h/, tentacles.]
[Illustration: PLATE LIX. Different forms of Balanus. (After Darwin.)
Cenobita diogenes.]
GENUS ^Balanus^
/Balanus/ is known as the "acorn-shell," or "sea-acorn," and is found
in vast numbers and of all sizes between tide-marks, incrusting rocks
and the piles of piers. It also may be found attached to floating
objects or to shells, or even to living animals, but its usual
habitat is stationary. Unlike /Lepas/, it has no stalk, the shell
being directly attached to some object. The body is surrounded by a
fold of skin, to which are attached a shell consisting of six or more
plates and a fourfold lid, or /operculum/, consisting of two /scuta/
and two /terga/. The operculum may be called the door, as the animal
opens and shuts it at will and has complete protection when it is
closed. If one taps a rock [pg255] incrusted with barnacles, and
holds the ear near, the closing of the many doors may be distinctly
heard.
The development of /Balanus/ from the larval stage, as also the
anatomy of the adult, is similar to that of /Lepas/. When covered
with water and unmolested, there may be seen over a bed of barnacles
thousands of tiny fringed feet waving to and fro. The motions look
like gestures; they are perfectly regular and rapid, numbering
eighty to a hundred a minute. The shell covering formed by barnacles
on piles of wharves and bridges is said to be a protective agent;
otherwise the barnacles seem to have no economic value in nature,
as, unlike other animals, they do not serve, except in very small
measure, as food to other classes. The tautog and perhaps some other
fishes feed partly upon them. They are sometimes an obstacle to
oyster-culture, as they fasten upon the objects intended for oyster
embryos, and, growing faster than the latter, soon crowd them off.
One species, /Coronula diadema/, fastens to the skin of whales. It
attains the size of two inches in diameter. The shell is half an
inch thick and full of cavities, into which the skin of the whale is
drawn, giving the barnacle a secure hold. (Plate LIX.)
^B. balanoides^ (Stimp.), ^B. ovularis^ (Gould), the rock-barnacle.
This is perhaps the most conspicuous of the barnacles. It inhabits
the whole northern Atlantic coast, and is so abundant that it not
only whitens the rocks with a complete incrustation of shells, but
the animals are so crowded that many of them lose their normal
shapes and become greatly elongated. When the rocks are covered
with water they seem alive, on account of the thousands of waving
tentacles. This species also incrusts woodwork between tide-marks.
The shell is small, white, and variable in shape; sometimes its
height is less than the diameter of its base; again the height is
several times greater and the summit broader than the base. In its
early stages the valves are smooth, but later the base is scalloped
by four or five grooves. The summit of the plates is even and
blunt. The aperture is diamond-shaped. Two valves of the operculum
are pointed at the tips; two are blunt, making a deep notch in
the summit. These valves are the distinctive feature by which to
recognize this species, which varies so much in outward form; the
species is also distinguished by its membranous base, which does
not form a solid plate like that of other species.
^B. eburneus^, the ivory barnacle. This species, like /B.
balanoides/, is a very common barnacle, and is found on all kinds
of submerged woodwork, whether fixed or floating. It is also found
on the carapace of [pg256] crabs and /Limulus/, and on mollusks.
It is chiefly found on objects below low-water mark. It ranges
from Massachusetts Bay to Florida. It is easily distinguished from
the preceding by its low, broad form and shelly base. The shell is
smooth and circular at the base, and inclines backward, forming an
oblique cone with a triangular opening; the plates terminate in
points at the summit and incline backward, the last one forming a
kind of beak. The operculum is pyramidal; two of its valves have
both transverse and longitudinal lines well defined at the base,
and are coarsely toothed at the edges; the posterior valves are
slightly grooved across.
^B. rugosus^ (Gould), ^B. crenatus^. Shell white, cylindrical,
somewhat conical, rugged, the summit usually as broad as the base;
height often greater than diameter; aperture diamond-shaped, plates
ending at the summit in acute spreading points, the posterior plate
folded and curved like a beak; plates rough, with coarse, irregular
ribs; valves of the operculum at the summit acute, with diverging
points; the points striated. Found on shells and stones in deep
water and also on bottoms of ships.
^B. geniculatus.^ Shell dirty greenish-white, cone-shaped; aperture
about the size of base; shell-plates triangular, unequal in
breadth, and with alternate large and small ribs; the smaller ribs
compressed and roughened on the edges by the conspicuous lines of
growth which run across them; depressed areas between the plates
marked with fine cross-lines; front valves of the operculum have
coarse plated ridges, which incline over one another and are
crossed by fine radiating lines; diameter at base one to one and
a half inches; height two thirds the diameter. Found on pecten
shells, and abundant off the coast of Maine.
^B. tintinnabulum.^ Shell pink to purplish, conical, with six
triangular plates, which are grooved, forming unequal ribs, and
crossed by distinct lines of growth; spaces between plates crossed
by lateral lines; posterior valves of the operculum longer than the
others and curved forward, resembling the beak of a bird of prey;
diameter at the base one inch; height one and a half inches. Found
in warm waters and on vessels from the South.
SUBORDER ~RHIZOCEPHALA~
These are parasitic forms and very degenerate. ^Sacculina^ lives on
crabs, and its term of life is about three years, during which period
the afflicted crab does not moult. Its shape is that of an ovoid sac
on a stalk, which it attaches between two segments of the ventral
surface of its host. The stalk divides and ramifies in a root-like
manner within the body of the crab, from whose vital elements it
absorbs its nourishment. The roots spread like a mycelium through the
whole crab, even to the claws.
^Peltogaster^ lives on hermit-crabs. [pg257]
SUBCLASS =MALACOSTRACA=
This subclass comprises highly organized /Crustacea/, usually of
considerable size, having the appendages much differentiated, the
thorax with eight segments, and the abdomen with seven segments.
ORDER =SCHIZOPODA=
The name, meaning "cleft-footed," applies to the appendages of the
thorax, which are once-branched (/biramous/). Gills, when present,
are attached to these feet, and hang freely in the water. A delicate
carapace covers the thorax; the abdomen is proportionately very
large, often twice the length of the cephalothorax. In /Mysis/ the
eggs are carried in pouches under the thorax, giving the common
name of "opossum-shrimp" to this small, transparent, phosphorescent
crustacean.
[Illustration: /Mysis sternolepis./]
GENUS ^Mysis^
^M. sternolepis.^ About one inch in length; translucent; antennæ
very long; segments marked at joints with dark spots; the last two
segments terminate in a stout spine; telson longer than the sixth
segment; the sides are nearly straight and are armed with spines;
the extremity is cleft; eyes large and prominent. Found abundantly
in winter on the shores of still, muddy bays and sounds, especially
among eel-grass.
ORDER =DECAPODA=
("/Ten-footed/")
The /Decapoda/ are named from their ten walking-legs. The higher
forms of crustaceans belong to this order. All the /Decapoda/
have a similar anatomy, but are placed in two subdivisions
[pg258] according to their external form. In /Macrura/, the first
subdivision, belong the lobsters, crawfish, shrimps, prawns, and
hermit-crabs, animals having a long and more or less cylindrical
body, with the abdomen extended; in /Brachyura/, the second
subdivision, are placed the crabs, animals having the thorax broad
and flat, and the abdomen bent under the thorax. The /Decapoda/
have twenty segments, all of which, except the last one, have, at
some period of life, a pair of appendages. The first two pairs of
appendages, or, in the stalk-eyed forms, the first three pairs,
are especially connected with the senses, and are often fringed
with hairs, which are also considered to have a sense-function. The
/antennules/, or first pair of appendages after the eye-stalks, are
sometimes divided into two or three branches. At the base of the
antennules are the ears. The /antennæ/, or second pair of appendages,
are undivided, but are larger than the first pair, and are often
very long. At the base of the antennæ are the renal glands. Both
the antennules and the antennæ are slender, elongated, movable, and
full of joints. In some species they are greatly modified, as in
/Scyllarus/, where they are developed into broad swimming-plates and,
perhaps, as shovels for burrowing; in some amphipods they are used as
swimming-organs. (Plate LX.)
[Illustration: PLATE LX. External Anatomy of a Lobster. /C/,
carapace; /e/, eye; /g/, gill; /m/, metastoma; /n/, endopodite; /p/,
epipodite; /x/, exopodite; I-VII, abdominal segments; 1, antennula;
2, antenna; 3, mandibles; 4, 5, maxillæ; 6, 7, 8, maxillipeds; 9, big
pincer; 10-13, walking-feet.]
The next six pairs of appendages are grouped about the mouth. They
are the /mandibles/, the /maxillæ/, and the /maxillipeds/. The
mandibles are at the mouth-opening, and, being heavy and hard, are
adapted to tearing and grinding; they have a jointed attachment,
the /palpus/, whose office is to keep the mandibles clean. The two
pairs of maxillæ are delicate and leaf-like. The three pairs of
maxillipeds grow gradually larger, the last pair being very prominent
and extending over the other mouth-parts. Next come five pairs of
walking-feet. One or more pairs of these feet have pincer-like ends,
or claws. Some species have the claws immensely developed, as in
lobsters. The claws are the /chelæ/, and the feet which bear the
/chelæ/ are termed the /chelipeds/. The rest of the walking-feet
have generally single, hook-like ends, but are variously modified
in different species. The abdominal segments have six pairs of
appendages, also variously modified. The last segment is without
appendages, but often is extended into a tail, [pg259] or
fin-like expansion. The next to the last segment, in many forms, has
appendages modified into swimming-plates, which extend on each side
of the telson, forming a broad, fan-like caudal extremity.
They have, then, to correspond to the twenty segments of the body,
two pairs of sensory, six pairs of mouth-, and five pairs of
walking-appendages attached to the cephalothorax, and six pairs on
the abdomen. The terminal segment, or telson, is without appendages.
The exopodite is present on the maxillipeds, but disappears from the
walking-feet in the higher forms.
In moulting the /Macrura/ split in the longitudinal line down the
back; in the /Brachyura/ the split occurs across the body at the
point between the thorax and the abdomen.
SUBORDER ~MACRURA~
SHRIMPS, PRAWNS, LOBSTERS, CRAWFISH, AND HERMIT-CRABS
The characteristic features of the /Macrura/ are an elongated body
with the abdomen usually extended; a carapace, somewhat cylindrical;
and the last pair of appendages of the abdomen (which are attached to
the next to last segment) united with the last segment, or telson, to
form a powerful caudal fin, used for swimming backward. The creeping
forms in moving walk forward, but swim backward.
FREE-SWIMMING FORMS: SHRIMPS AND PRAWNS
In these animals the body is compressed and the carapace is not hard.
The abdomen is very large in proportion to the cephalothorax, and has
a peculiar bend. The rostrum is often longer than the thorax. The
eye-stalks, antennæ, and legs sometimes attain extraordinary length,
and the chelæ (claws) are not always on the first pair of legs. In
some species chelæ are on two or three pairs of the legs. Above the
antennæ are expanded antennal scales, which, together with the long
bases of the antennules and very prominent eye-stalks, make the head
a broad and conspicuous feature. The difference between shrimps and
prawns is not very well defined, the small individuals seeming to
be generally called shrimps, the larger full-grown ones prawns.
[pg260] Prawns are known as /crevettes/ in France and as /Garnelen/
in Germany, where they are largely used as food. In the United States
the shrimp-fishery is an industry of the South. On the California
coast the fisheries are very extensive and are monopolized by the
Chinese.
GENUS ^Penæus^
^P. setiferus.^ This species is about six inches in length when
full-grown. A ridge or crest extends along the center of the
carapace, and terminates in a long, pointed, toothed rostrum,
the teeth being fringed with hair on the inner side. The antennæ
are a foot or more in length; there are chelæ on the first three
pairs of thoracic feet; the swimming-feet and lateral margins of
the segments of the abdomen are fringed with hair; and the caudal
appendages are longer than the telson. It ranges from Virginia
southward, and is very abundant on the shores of the Southern
States, where it is gathered for the markets. The large ones are
known as prawns and the small ones as shrimps.
^P. brasiliensis.^ This species is associated with /P. setiferus/,
and, although not so abundant, forms a part of the shrimp-supply
in the fisheries. It differs from the former in having a groove
on each side of the ridge which runs through the center and whole
length of the carapace. The first three pairs of feet are chelated.
This shrimp is found as far north as Long Island, and often in
brackish water, or even where the water is quite fresh.
GENUS =Palæmonetes=
^P. vulgaris (Palæmon vulgaris).^ Average size one half of an inch
in length; body translucent, almost colorless, irregularly spotted;
rostrum as long as carapace and toothed on the upper edge. It is
found among eel-grass in brackish water, and also in pools and
ditches on muddy shores from Massachusetts Bay to Florida. Commonly
known as prawns.
[Illustration: /Palæmonetes vulgaris/; male.]
GENUS ^Crangon^
^C. vulgaris^, the common sand-shrimp. It ranges from Labrador to
North Carolina on the Atlantic coast and from Alaska to southern
California on the Pacific coast. It is found in abundance on sandy
shores at low-water mark, and in shallow water below tide-mark;
also among rocks and seaweeds. When left by the tide it buries
itself in the sand. Its color varies with its location, rendering
it inconspicuous. Upon the [pg261] sandy shores it is translucent,
pale in color, and often specked, closely resembling the sand,
while on dark, muddy bottoms it is much darker. This is an edible
shrimp, eagerly devoured by fishes; it is also gathered for the
markets. The body of /C. vulgaris/ is broad at the anterior end
and tapers to a sharp point at the posterior extremity. A pair of
broad, divided appendages on the cylindrical segment, which is next
to the last on the abdomen, together with the sharp telson, form a
fan-like swimming-tail. As in all shrimps, the antennæ are long and
have plate-like antennal scales at the base, which are fringed with
hairs. The mandibles are long. The movable finger of the chela is
folded across the extremity of the claw.
^C. franciscorum^, the California shrimp. This species is about
three inches in length. It is distinguished from /C. vulgaris/ by
its larger size and by the greater length of the movable finger of
the chela, which folds parallel to the side of the claw instead of
across its extremity. Its color is light or dark yellowish-gray,
mottled. This is the shrimp extensively gathered by the Chinese for
commercial purposes. The shrimp-meat is dried and cured, and then
separated by blowers very much as wheat is cleaned. It is exported
to Eastern countries in great quantities, the value of the export
being estimated at one hundred thousand dollars per annum.
[Illustration: /Crangon vulgaris/, the common sand-shrimp; male,
natural size.]
CREEPING FORMS: LOBSTERS AND CRAWFISH
FAMILY ~ASTACOIDÆ~
GENUS ^Homarus^
There are but three species of this genus, which is the most
important one of all the /Crustacea/. They are /H. vulgaris/ of
Europe, /H. capensis/ of the Cape of Good Hope, and /H. americanus/,
which occurs on the eastern coast of the United States from Labrador
to New Jersey. The lobster-fishery is one of great importance, and of
such value that it is governed by stringent laws. The [pg262] annual
catch on the Atlantic coast of North America amounts to many millions
of lobsters, the money value of which is very large.
^H. americanus^, the common lobster of the Atlantic coast.
The characteristic feature of the lobster is its enormously
developed chelæ, or pincer-claws, which are on the first pair of
walking-feet. Small claws occur on the next two pairs, and simple
hooks on the remaining two pairs. The appendages on the abdomen are
divided (biramous). In the female they are used, excepting the last
pair, for holding the eggs; in the male they are greatly abridged.
The appendages on the next to last segment are divided and broadly
flattened, forming with the telson a powerful swimming-paddle. The
rostrum is very prominent, and has a long, pointed end, slightly
upturned, and several spines.
The lobster belongs to the creeping forms of the order; it walks
forward by means of the ten feet, but swims backward by using its
caudal fin. It lives in deep water on rocky bottoms, hiding among
stones, etc., but frequents sandy shores as well. It lives on
dead and decaying animal matter, and it would seem strange that
its flesh is so palatable, were it not that we know that chemical
combinations which take place in the assimilation of food make one
kind as clean, when transformed, as another. All the crustaceans
have a similar dietary, being scavengers of the sea; yet fishes
find them more acceptable than other animal food, and fishes
capable of capturing larger prey subsist largely on the minute
entomostracans described elsewhere.
[Illustration: /Homarus americanus/, American lobster; male.]
The lobster is so large that it can easily be dissected, and will
serve as a type of the structure of /Crustacea/. In dissecting one
can follow the descriptions given of the anatomy of /Crustacea/
on page 246, and will be interested in observing the beautiful
arrangement of the parts and their adaptation to the uses they
serve. [pg263]
The female lobster carries her eggs on the abdominal legs, to which
they are glued by a kind of cement. After the young emerge from
the egg, the zoëæ still cling to the mother for a little time.
The lobster moults eight times the first year, five times the
second, and three times the third year, after which the male moults
twice and the female once a year. It retires to some secluded
spot for this operation, which is attended with many dangers. The
back splits open longitudinally and the animal slowly withdraws,
leaving the shell complete. In preparation for moulting, the lime
around the contracted joints of the chelæ is absorbed, so that the
soft flesh can pass through. Any injury to a limb at the time of
moulting, or which results from fighting or from any accident, is
repaired at successive moultings, and a lost member is replaced by
a new, but not always a perfect, one.
GENUS ^Panulirus^
^P. interruptus.^ This is the California spiny lobster,
rock-lobster, or salt-water crawfish. It differs from the common
lobster /Homarus/ of the Atlantic coast in having no large claws,
the first pair of feet being simple like the rest, also in having
antennæ which are enormously long and very large at the base. The
carapace is beset with spines, and the lateral margins of the
abdominal segments end in spines. This species lives among the
rocks on the southern California coast.
[Illustration: /Panulirus interruptus/, the spiny or rock-lobster.]
^P. argus^ or ^americanus^ resembles /P. interruptus/, and is found
on the coast of Florida.
GENUS ^Scyllarus^
/Scyllarus/ has a broad, almost square carapace, which is uneven and
coarsely granulated; the anterior corners are sharp, the posterior
ones rounded. The antennæ are curiously modified into broad, flat,
double plates reaching quite across the straight anterior end of the
carapace. The under scales of these modified antennæ are rounded and
leaf-like, the upper ones are pointed. The margins of the abdominal
plates on the ventral side are toothed, and on the upper side the
first three sections have [pg264] knobs, the third one being the
most prominent, and forming the posterior extremity when the abdomen
is folded in. The walking-feet are all simple and end in points;
the first pair are the longest, and the following ones gradually
diminish in size. The ventral surface is rough and spiny. The abdomen
is of about the same length as the carapace. These animals are found
off the Florida coast and are caught in the fish-traps. They are
uncommon. The very peculiar development of the antennæ makes them
worthy of examination when opportunity offers.
ANOMALOUS FORMS: ANOMURA
The anomalous forms which are intermediate between the suborders
/Macrura/ and /Brachyura/ were, until recently, placed in a suborder,
/Anomura/. The members of this group differ from one another, and
some of them resemble in external features members of the other
divisions of the suborders, but there is a difference in anatomical
structure which separates them in the classification.
FAMILY ~DROMIDÆ~
GENUS ^Hippoconcha^
^H. arcuata.^ This curious little crab, found on the Florida coast,
carries the half of a bivalve shell over its back. Its fifth pair
of thoracic legs are bent over the back, and these, together with
the fourth pair of legs and the spiny front edge of the carapace,
enable the crab to hold the shell in position. This crab was
formerly classed with the hermits, all of which were originally
called /Bernhardus/, after the monk of that name.
FAMILY ~PAGURIDÆ~
THE HERMIT-CRABS
In these curious animals the posterior part of the body is not
protected by a crustaceous covering, and therefore the animal seeks
protection by inserting its soft and defenseless abdomen into some
hollow object, usually the shell of a gasteropod mollusk, as the
whelk or the periwinkle (/Buccinum/, /Littorina/). The hermit-crabs
do not always use a shell for this purpose, as they are sometimes
found in the tubes of plant-stems or in sponges. Like other
organisms in the animal world, they seem [pg265] well fitted to
make the best of their surroundings, the body becoming modified to
suit the peculiar conditions under which they live. In those which
inhabit shells the abdomen becomes spiral, in conformity to the
convolutions of the shell. All the abdominal appendages are more or
less atrophied; the sixth pair become like hooks, and these fasten
to the columella of the shell, keeping the crab securely attached
to it. In the female some of the abdominal appendages are hair-like
and are adapted to carrying the eggs. The thorax, being protected,
is protruded from the shell at will. The first pair of feet are much
larger than the others, and are provided with claws (chelæ). The
first right foot is usually much larger than the left, and, besides
the usual functions of capturing and crushing prey, the claw, or
hand, serves as an operculum to close the mouth of the shell when the
crab retires completely within it. The small left hand is shaped to
fill out the parts of the opening not covered by the right one, thus
making a close fit. The next two pairs of feet end in simple hooks,
and are used for walking and dragging the crab along when he travels.
These crabs move about very fast, and the houses upon their backs
seem no encumbrance. [pg266]
[Illustration: /Pagurus bernhardus/: /ch/, chela of first right leg;
/l./4, /l./5, fourth and fifth legs; /t/, abdominal terga; /up/, last
pair of appendages, modified to fasten to the columella of the shell
in which the hermit lives.]
In some genera both hands are alike; in others the left one is the
larger. In the case of hermits which live in tooth-shells, the
right hand is cylindrical in form, fitting the circular opening of
the shell. The other extreme is found in the genus /Cancellus/,
where both the chelipeds and the first pair of ambulatory feet are
ingeniously shaped, so that when closed they form a round operculum,
or door, which closes the way into the compact sponge which this crab
has for its carcin[oe]cium, or house. It is interesting to note these
differences and observe the perfection with which the feet are formed
and jointed to suit the openings of different shells. Some genera
show other adaptations to their twisted houses, the eye-stalks being
uneven in length and the ambulatory feet unequal on the opposite
sides. Besides this, some species are hairy and cover themselves with
dirt for further protection. The exposed claws of some hermits have a
special armature of spines, which make a fringe of points around the
opening of the shell when the crab is withdrawn.
As the hermit grows he is occasionally obliged to find a new or
larger shell, and there are amusing anecdotes of the troubles he
experiences at these times while house-hunting. Very often he tries
several shells before he finds one to fit. There is a tradition,
not, however, well authenticated, that if the shell chosen happens
to be occupied by its natural owner, the crab tears out and devours
the unfortunate occupant. If the desired shell is occupied by
another hermit inferior in strength to himself, he proceeds to take
possession by violence. He then examines carefully the empty shell,
inserting his legs and feelers, and if he decides to occupy it he
withdraws his abdomen from the old shell and darts it so quickly into
the new one that the act of transference is difficult to follow.
After walking about with the new shell it sometimes proves to be
unsatisfactory and further search becomes necessary. After it is
well domiciled the crab never ventures outside the shell until it
is obliged to change again on account of growth, or because some
stronger crab dispossesses him. The shells of hermit-crabs serve
frequently as the home of other animals which live with them a
commensal life. The hydroid /Hydractinia polyclina/ often covers
the exterior of such shells with a brown, velvety growth. Some
sea-anemones also are commensals [pg267] with hermits. /Adamsia
palliata/ is always found on the shell occupied by /Eupagurus
prideaux/, and never on any other. This is a European form. On
our own coast a red anemone, the /Epizoanthus americanus/, found
in deep water off the entire eastern shore, fastens on the shell
occupied by the hermits /Eupagurus pubescens/ and /E. kroyeri/. This
anemone in time absorbs the shell of its host and itself becomes its
protector--an advantage to the hermit, who finds room in the yielding
polyp-mass for its increasing size, and feels no longer the necessity
for change of domicile. The female hermit holds its eggs in the
posterior feet until they are hatched; the young are then released,
pass into the water, and soon find shells for themselves.
[Illustration: A colony of sea-anemones (/Epizoanthus americanus/)
which had completely covered and absorbed a shell occupied by a
hermit-crab (/Eupagurus pubescens/), which still lived within the
cavity. The polyps are not expanded.]
GENUS ^Pagurus^
^P. bernhardus.^ This is a large species, bright red in color,
rough and hairy. It inhabits the shells of /Fulgur carica/ or
of /Polynices heros/. It ranges from Cape Cod northward, and is
replaced on the northern California coast by /P. alaskensis/ and
/P. aleuticus/.
[Illustration: /Pagurus bernhardus/, the hermit-crab.]
^P. pollicaris.^ This hermit inhabits shells similar to those
occupied by the last, but is pale red in color, and its surface
is granulated and not hairy. The short joint of the chela has a
broad angle. It ranges from Massachusetts to Florida, and occurs at
low-water mark on rocky and shelly bottoms of bays and sounds.
^P. longicarpus.^ A quick-moving little hermit with long chelipeds,
found in small shells at the water's edge in quiet places. They
exist in great numbers and are eaten, shell and all, by fish. This
species can be distinguished from all others by its very light
color and metallic luster.
GENUS ^Clibanarius^
^C. vittatus.^ This hermit is found from North Carolina southward
along the edge of the water and in tide-pools. It cannot be
mistaken [pg268] for any other hermit common on our coast, since
it has the very distinctive feature of white longitudinal stripes
on the ambulatory feet. The chelipeds are about equal, rough with
tubercles, and the tips have smooth black edges. Body and feet are
quite hairy. The color is brown and white.
GENUS ^Pylopagurus^
This genus is represented in Southern waters by several species.
One of the most characteristic of them lives in /Dentalium/, the
tooth-shell. The outer surface of the right hand is formed to close
the shell. All the ambulatory feet and the very small left hand fold
beneath, leaving only the flat surface of one hand exposed to view.
Another species lives in a shell covered with polyzoans.
FAMILY ~CENOBITIDÆ~
GENUS ^Cenobita^
^C. diogenes.^ This large hermit-crab, found in Florida and in more
southern waters, inhabits the beautiful pearly shell of /Livona
pica/. It lives on land a part of the year, but spends the breeding
season in the water. It can be distinguished by its land-roaming
habits, its large left cheliped, very stout walking-legs, and
compressed eye-stalks. This species climbs the hills, but is more
frequently met with in low, shaded, marshy places. (Plate LIX.)
FAMILY ~HIPPIDÆ~
GENUS ^Hippa^
[Illustration: /Hippa talpoida/, the sand-bug.]
^H. talpoida.^ This animal, commonly known as the "sand-bug,"
differs greatly in appearance from a crab. When the appendages are
folded under the carapace it somewhat resembles an egg, the body
being ovate, about half as broad as long, and the sides forming a
nearly regular curve. The carapace is about one and a half inches
long, convex, yellowish-white, and nearly smooth. The abdomen is
long and pressed under the body, reaching nearly to the front.
The eyes are minute and on the ends of long, slender stalks. The
antennæ are plume-like and about as long as the carapace. /Hippa/
lives on sandy beaches at or near low-water mark, exposed to the
action of the waves. It burrows with great rapidity into the loose
and shifting sands, using the short and stout second, third, and
fourth thoracic legs and the appendages of the sixth abdominal
segment [pg269] for pushing and digging. Crabs of this species
are gregarious and may be seen in great numbers, though but few
will be captured together by digging, as they rapidly disappear
beneath the sand. Sometimes they are found swimming about in the
tide-pools. They seem to live upon the organic particles contained
in the sand, which they swallow, the mouth not being adapted for
mastication. This species ranges from Cape Cod to Florida. (Plate
LXI.)
^H. analoga.^ Similar to /H. talpoida/, but broader and flatter. It
is bluish above, yellowish-white below, and the fringing hairs are
black. Found on the California coast.
GENUS ^Albunæa^
^A. gibbesii.^ This animal is found with /Hippa/, and, like it,
burrows rapidly in the sand. Its general outline is square. The
surface of the carapace is marked off with denticulated lines,
which make the back appear as if composed of plates. The front edge
of the carapace has a row of teeth and a prominent spine at the
anterior angles. The abdomen is doubled under itself (not fitting
into a groove of the thorax, as in ordinary crabs), this animal
being intermediate between the long- and the short-tailed forms.
The eyes are on triangular, plate-like stalks. The antennules are
very long and are fringed with hair. The chelipeds have claw-like
joints, which close across the straight, broad end of the hand.
The first two pairs of walking-feet have curious sickle-like
terminal joints. The animal is about one and a quarter inches long.
/Albunæa/ does not extend as far north as /Hippa/, its range being
from Georgia southward. (Plate LXI.)
FAMILY ~PORCELLANIDÆ~
The crabs of this family are little more than one quarter to one half
of an inch across the back. The chelipeds are broad and flattened.
The first three pairs of walking-legs are well developed, and the
fifth pair are very small and are doubled over the base of the
carapace. The sixth segment of the abdomen has a pair of biramous
appendages, which, with the telson, form a swimming-fan.
GENUS ^Porcellana^
^P. sayana.^ Carapace little longer than broad; breadth about one
quarter of an inch; smooth; has three acute denticulations between
the eyes, the middle one the largest and depressed in the center;
two denticulations on each anterior side; chelæ fringed with hair
on the edges; walking-legs somewhat hairy; fifth pair of legs
folded over base of carapace; color reddish, with white spots.
This species was once called /occulata/, because of the eye-like
spots over its entire surface. The posterior part and abdomen have
longitudinal bands of color. The claws are marked like the shell.
Found from South Carolina southward, often in the shells inhabited
by hermit-crabs. (Plate LXI.) [pg270]
GENUS ^Petrolisthes^
^P. sexspinosus.^ Carapace longer than broad; breadth about one
half of an inch; space between the eyes broad, but not divided into
three teeth as in /Porcellana sayana/; second joint of the cheliped
has five broad teeth on its front edge and five or six small
spines on its outer edge; fifth pair of legs doubled over base of
carapace; whole body traversed with broken red lines. Found from
South Carolina southward. (Plate LXI.)
^P. armatus.^ Carapace longer than broad; breadth about one
quarter of an inch; prominent and wide between the eyes; a small
sharp spine on each anterior side; chelipeds long; second joint
of cheliped twice as long as broad, with three teeth on the front
edge and four or five small spines on the outer edge. Found on the
Florida coast. (Plate LXI.)
FAMILY ~LITHODIDÆ~
The species of this family have a broad, ovate, uneven body and
a prominent rostrum. The fifth pair of legs are rudimentary and
are folded under the carapace in the branchial chambers, so that
the crabs appear to have but four legs on each side. This is
the distinguishing feature of the family, and makes them easily
recognized.
GENUS ^Lithodes^
^L. maia.^ The carapace is cordate (heart-shaped), and longer than
broad, exclusive of the rostrum. The margin is recurved all around,
and is beset with numerous very long spines. Six spines on each
anterior side margin are regular and longer than the others. The
surface of the carapace is covered with tubercles and spines and
elevated in places. The rostrum is spiny, a third as long as the
carapace, and has two spines at the base, one above the other,
a spine at each side, two lateral spines near the middle, and
two terminal divergent spines. The chelipeds are unequal and are
covered with spines, those on the inner margin being the longer.
The color is yellowish-red, lighter underneath; the spines are
darker. Found on the fishing-banks off the coast of Maine. (Plate
LXI.)
[Illustration: PLATE LXI. 1, Hippa talpoida. 2, Albunæa gibbesii.
3. 1, Porcellana sayana; 2, Petrolisthes armatus; 3, Petrolisthes
sexspinosus. 4, Lithodes maia.]
[Illustration: Plate LXII. Echidnocerus cibarius. Cryptolithodes
sitchensis. Echidnocerus foriminatus. Phyllolithodes papillosus.]
GENUS ^Echidnocerus^
^E. cibarius.^ This curious crab has the carapace raised in front
into a large cone-like elevation terminating in a long point. Three
prominent but smaller cones extend across the center of the back,
and two still smaller ones occur on the posterior sides and in the
middle of the posterior margin. The whole surface of the carapace
is covered with coarse granulations arranged in rosette-like
groups. The chelipeds and legs are beset with large tubercles and
fold together in such a manner that when retracted the crab is a
close, compact, box-like mass, with a very rough, [pg271] spiny
armature. The antennæ are broad at the base and covered with small
spines on the sides and upper surface, and the eye-stalks are also
spiny. This crab sometimes attains the size of ten inches across
the carapace and a weight of seven pounds, being among the largest
crabs known. It is found at the mouth of the Columbia River and
along the northwest coast. (Plate LXII.)
^E. foriminatus.^ This species resembles /E. cibarius/ in the
manner of closing the feet, forming a compact, box-like, spiny
armature. The body is more depressed than that of the latter,
and the cone-like elevations on the back are less prominent. The
spines are hairy. The characteristic feature of this species is a
semicircular cut in the second joints of the chelipeds, directly
opposite to similar depressions in the first walking-legs, so that
when the feet are folded a round hole is left, through which water
flows freely to the gill-openings, which might, without these open
holes, be obstructed by the close folding of the legs against the
carapace. Found off the California coast near San Francisco. (Plate
LXII.)
GENUS ^Acantholithodes^
^A. hispidus.^ The whole body in this species, including the legs,
is covered with hairy spines. The abdomen is broad, and covers
about the whole under surface of the body, and is also beset with
hairy spines, but they are less prominent than those on the upper
side. The rostrum, terminating in spines, reaches to the tips of
the eye-stalks, which are also spiny. The chelipeds are larger and
longer than the walking-feet; the latter taper to a point, ending
in a sharp nail. The shape of the body resembles somewhat that of
a toad. This is a deep-water species, but it is sometimes brought
ashore at Monterey, California, by fishermen who find it in the
stomachs of fishes.
GENUS ^Cryptolithodes^
^C. sitchensis.^ The most striking characteristic of this singular
species is the great development of the carapace, which forms
a broad, thin shield extending beyond the body and legs, and
completely hiding the animal beneath it. The carapace is smooth
and uneven, has a high ridge through the center of the anterior
part, and the sides are broadly expanded and bluntly pointed at the
extremity. The rostrum appears like a small rectangular piece cut
out of the anterior side of the carapace. This species is found in
the Strait of Fuca. A similar species, /C. typicus/, is found near
low-water mark on the surf-washed rocks of the beach at Monterey,
California. (Plate LXII.)
GENUS ^Phyllolithodes^
^P. papillosus.^ The carapace is triangular, about two inches
wide at the base, and narrowing to a long, pointed rostrum which
terminates in a forked spine. The surface of the carapace is deeply
depressed in parts, and forms a heart-shaped figure in the center.
The lateral margins have four prominent spines on each side, the
two at the posterior ends being [pg272] thicker than the other
two. The abdomen is broad, covering the whole under side of the
body, and is marked off with prominent raised ridges diverging from
the center line. The legs are all beset with long, rough spines.
Habitat, the northwest coast. Taken from the stomachs of fishes off
Monterey, California. (Plate LXII.)
SUBORDER ~BRACHYURA~
THE CRABS
This group contains the true crabs, which are the highest of the
/Crustacea/. In form they are quite the reverse of the first group.
In the /Macrura/--except in the anomalous forms--the body is long
and cylindrical and the abdomen extended, but in the /Brachyura/ the
body is flat and broad and the abdomen short and reflexed. Crabs of
this suborder inhabit all seas of the globe, and are found from the
shore to great depths. Some species live on land, some on the shore,
some in deep water. Some forms burrow in the sand; others live under
stones and boulders, or conceal themselves in crevices of rocks or
in the cavities of sponges. They are divided into many families,
and creep, climb, swim, or burrow, their structure being modified
to their respective modes of life. There is also great variation in
their shapes as well as in their color and markings. This diversity
is so great and peculiar that it seems as though each one were more
curious than the others.
In crabs the cephalothorax is depressed and often broader than long.
The abdomen is relatively small and is folded under the thorax, lying
in a groove which it fits so perfectly as to be quite hidden from
above. The appendages of the abdomen are much reduced in number. The
male has two pairs; the female has four pairs, which it uses for
carrying its eggs. The first pair of walking-legs are comparatively
large, and end in chelæ, or pinching-claws. The other eight legs
terminate in simple points, except in the swimming varieties, when
the fifth pair is flattened to form fins, or swimming-paddles. The
eye-stalks are long and fit into sockets on the carapace. Both pairs
of feelers are small. The antennules are frequently folded into small
grooves. The external or third pair of maxillipeds are broad and
flat, and cover the mouth-parts like a lid, or operculum. [pg273]
Crabs, like other crustaceans, are scavengers, living on dead animal
matter; but the land species are also vegetarian in diet. They are
great fighters, but are also wily, often averting danger by resorting
to stratagem. They are an interesting and curious group, as they
possess a good degree of intelligence and have amusing habits.
From the time they leave the egg until they attain the adult form
they pass through several complete and singular metamorphoses. The
most marked forms are called the /Zoëa/ and the /Megalops/. So little
do these resemble the adult that originally they were classed as
distinct genera far removed from the one to which they really belong.
After the larva has moulted several times it appears as in the
illustration on page 248--the last zoëa stage. From this it changes
directly to /Megalops/; the /Zoëa/, seeming to be attacked with
violent convulsions, wriggles out of its skin a full /Megalops/ (page
248). The animal then has enormous eyes, an extended abdomen, an
elongated carapace, and swimming-legs. This stage is a short one, and
at the first moulting changes to a form nearly approaching the adult.
From this time they grow by shedding the shell at certain periods.
This shedding is supposed to occur twice each summer until they have
reached full growth, after which it is probable that they do not
again moult; for often they are found with extraneous organisms,
such as barnacles and sponges, upon them, of a size that must have
required a considerable period of time for growth. The sexes of
the same species sometimes differ so much that it is difficult to
classify them. Even naturalists have been led into the error of
assigning the male and female to separate species.
The front side margins of the carapace in many crabs are edged with
a row of teeth or with spines, which vary in number and character
in different species. In the spider-crabs the whole surface of the
carapace is generally studded with tubercles, spines, and stiff hairs
of a peculiar character. This armature is for protective purposes,
and is often used to secure foreign bodies, such as algæ, hydroids,
and polyzoans, which the crabs place upon their backs to disguise
themselves. The burrowing crabs are usually smooth. When in motion
the crab moves sideways, using the legs [pg274] of one side to pull
with and those of the other side to push with. As all the legs do
not move at the same time, a continuous and uniform motion is kept
up. Some species move with great rapidity, notably the sand-crab,
/Ocypoda arenaria/. Often when pursued they will run into the surf
instead of to their holes. The common edible crab, /Callinectes
sapidus/, of the Atlantic coast, the fiddler-crabs, and the
spider-crabs are among the well-known representatives of /Brachyura/.
FAMILY ~PORTUNIDÆ~
SWIMMING CRABS
GENUS ^Carcinides^
[Illustration: /Carcinides mænas/, the green crab.]
^C. mænas^ (M. J. Rathbun), ^Carcinus mænas^ (Leach), the green
crab. This is one of the most common species on the Atlantic coast
from Cape Cod to New Jersey, and is very abundant in Vineyard
Sound, Buzzard's Bay, and Long Island Sound. It is found between
tide-marks, frequently well up on the beach, hiding under loose
stones, also in tide-pools and in holes and cavernous places on
the shore. It is from one and a half to two inches long, and a
little more in breadth. It has five acute teeth on each side of the
anterior part of the carapace. Its color is green, spotted with
yellow, making it quite conspicuous. The surface of the carapace
and limbs is more or less granulated. The posterior feet are
flattened to form swimming-paddles. It is a very lively creature
and has reckless audacity when brought to bay, which justifies its
specific name (which implies frenzy). The French call it /crabe
enragé/. [pg275]
GENUS ^Callinectes^
[Illustration: /Callinectes sapidus/, the blue crab.]
^C. sapidus^ (Mary J. Rathbun), ^C. hastatus^ (Stimpson), the blue
crab. This is the common edible crab of the Atlantic coast. It is
known at the North as the "blue crab," and at the South as the
"sea-crab." It is found from Cape Cod to Florida, and after the
lobster is the crustacean which has the greatest commercial value,
being taken in immense quantities for the markets, not only when
the shell is hard, but immediately after moulting, before the new
shell has hardened, when it is known as the "soft-shelled crab."
It inhabits muddy shores, and is common in bays and at the mouths
of estuaries. The carapace is about twice as broad as it is long,
and has a long, sharp spine on each side which projects outward.
This is a distinguishing feature. There are eight short spines on
each side between the long spines and the eyes; then come recesses
for the eyes, and between the eyes are four unequal teeth and a
small spine underneath. The chelæ are large and somewhat unequal
in size; then come three pairs of simple feet and a fifth pair,
which are flattened, forming swimming-organs. The margins of the
carapace and abdomen are fringed with fine hairs, as are also most
of the joints of the limbs. The upper surface of the body and claws
is dark green in color, the lower surface is dingy white, the feet
blue, and the tips of the spines reddish. The body is compressed,
the carapace being moderately convex above, and is covered with
minute granulations, which are more numerous over some portions
than over others. The abdomen of the female is very broad and fills
the entire space between the bases of the posterior pair of feet.
During the spawning season it is so charged with eggs that often
it projects out almost at right angles with the carapace. The
[pg276] crabs of this species are very active and can swim rapidly.
They also have the habit of pushing themselves backward into the
mud for concealment. They are predaceous and pugnacious, and have
great strength in their claws, which they use with dexterity.
They not only fight their own kind, but show a bold front to all
enemies, including man. The average size is six inches across the
carapace.
GENUS ^Ovalipes^
[Illustration: /Ovalipes ocellatus/, the lady-crab.]
^O. ocellatus^ (Rathbun), ^Platyonichus ocellatus^ (Latreille),
the lady-crab or sand-crab. A species common on sandy shores from
Cape Cod to Florida. It is found among the loose sands at low-water
mark, even on the most exposed beaches, and also is abundant on
sandy bottoms offshore. At low-water mark it buries itself up
to the eyes and antennæ in the sand, where it watches for prey
and foes, and quickly disappears beneath the sand when danger
approaches. It possesses the power of burrowing in common with
other marine animals which inhabit exposed beaches of loose sand.
By burying itself deep in the sand it is protected from the action
of the breakers. This species is easily distinguished by the color
and shape of its carapace, taken in connection with its posterior
swimming-feet. The body is nearly as long as it is broad, with
five prominent spines on each side. The front margin is indented
on each side of a three-spined rostrum, to form cavities for the
eyes. The first limbs are large and have claws; the posterior ones
are flattened into swimming-feet, and the intermediate three pairs
are simple in structure, ending in points. In color it is white,
covered with spotted rings of red and purple. [pg277]
WALKING CRABS
FAMILY ~CANCROIDÆ~
GENUS ^Cancer^
[Illustration: /Cancer irroratus/, the rock-crab; male.]
^C. irroratus^, the rock-crab. This is the common crab of the New
England coast. It ranges from Labrador to South Carolina, but is
rare south of New Jersey. It is found on sandy as well as on rocky
shores at and below low-water mark and also between tide-marks,
hiding among rocks, nearly buried in sand or gravel, and in
tide-pools, where sometimes amusing combats between the males may
be seen. The carapace is suboval, one third broader than long,
the breadth being often from three to four inches. The surface is
granulated but smooth; the color is yellowish, closely dotted with
brown. The eyes are on short stalks in deep, circular holes, and
between the eyes are small teeth. There are nine blunt teeth along
each side of the front edge of the carapace. The first pair of legs
are short and stout, and terminate in claws. The four posterior
pairs are slender and end in pointed tips. This is an edible crab,
and it is devoured by the larger fishes, but does not--although
there seems to be no reason for it--share to any extent a place in
the markets with the blue crab, /Callinectes sapidus/.
[Illustration: /Cancer borealis/, the Jonah crab; male.]
^C. borealis^, the Jonah crab. This crab resembles, and is
frequently taken for, /C. irroratus/. It is larger than the latter
in full growth, and is heavier and more massive. The carapace and
claws are rougher, the granules being irregular in size. The legs
are proportionately shorter and heavier. The teeth on the anterior
margins are rounded in front, but the posterior ones are sharply
pointed. In color [pg278] it is brick-red above and yellowish
beneath. It inhabits rocky shores only and is found at low tide on
the surface of the rocks, where it is exposed to the action of the
waves and also to the attacks of birds of prey, which feed upon
it, while /C. irroratus/, concealed under the rocks in the same
locality, escapes their depredations. This species is supplied to
the Newport market, where it is considered preferable to the blue
crab. Its range is from the eastern end of Long Island to Nova
Scotia.
[Illustration: /Cancer magister/, the common crab of the Pacific
coast; male.]
^C. magister.^ This species inhabits the Pacific coast and ranges
from Alaska to Lower California. The adult male is from seven to
nine inches broad and from four to five inches long. The anterior
margin of the carapace is an almost regular elliptical curve with
nine small teeth on each side. At the end of the curve a large,
pointed tooth projects directly outward, and from this the carapace
slopes abruptly backward, giving a narrow posterior end. The
surface of the carapace is undulated and covered with papillæ, and
is light reddish-brown, shading to lighter color in the back. The
color of the legs and under surface of the animal is yellowish.
The claws are toothed above and ribbed at the sides. It inhabits
sandy bottoms below tide-mark and is the largest and most important
edible crab of the western coast.
^C. productus^, the red crab. This species, like the preceding one,
is of large size and inhabits the western coast from Alaska to
the Gulf of California. The carapace is four and a half inches in
length, from five to seven in breadth, and somewhat elliptical in
outline. The teeth on the anterior margin are distinctly separate
in the adult, but in the young appear as wrinklings of the edge
of the carapace. The posterior margins are concave. In color the
animal is dark red above and yellowish beneath in the adults, but
variable in the young, sometimes being yellow spotted with red,
or banded with red and yellow. It inhabits rocky shores. This is
an edible crab, but is not taken for the markets, /C. magister/
supplying all demands. [pg279]
[Illustration: /Cancer productus/, the red crab; male.]
[Illustration: /Cancer antennarius/, the California rock-crab.]
[pg280]
^C. antennarius^, the rock-crab of the Pacific coast. This
species of the California coast inhabits rocky bottoms below
low-water mark. The carapace is three and a half inches long by
five or six inches wide, and dark purplish-brown in color. The
chelæ are marbled with purplish spots and are nearly smooth. The
distinguishing features of this crab are its large and hairy
antennæ, the hirsute margins of its abdomen and walking-feet, and
the numerous hairs on the under side of its body.
GENUS ^Menippe^
[Illustration: /Menippe mercenaria/, the stone-crab; male.]
^M. mercenaria^, the stone-crab. This species lives in deep holes
in the mud along the borders of creeks and estuaries, and also
in crevices between fragments of rock, in stone-heaps and other
debris, and is found from South Carolina to Texas. These crabs are
edible, and in some localities are hunted for food, one manner
of capturing them being to thrust the hand and arm into their
holes and drag them out, an operation attended with danger to the
inexperienced hunter, who is likely to be badly pinched. They are
withdrawn with difficulty, as they offer a strong resistance,
bracing themselves with their claws against the sides of their
holes, and often hold so firmly to the rocks that they are torn
[pg281] apart. They are also taken by a hooked iron which is thrust
into the hole; the crab seizes it and is then suddenly jerked from
its hole. The adult measures about three by four and a half inches,
and the body is from one inch to two inches thick. One of the chelæ
is larger than the other, and both are proportionately enormously
large, and are tipped with black. The terminal joints of the other
four pairs of legs are thickly fringed with hairs and end in points
which seem like nails.
FORMER GENUS ^Panopeus^
[Illustration: /Eurypanopeus depressus/, the mud-crab; male, natural
size.]
^Eupanopeus herbstii^, ^Eurypanopeus depressus^, ^Neopanopeus
texana^, ^Rhithropanopeus harrisii^ (Mary J. Rathbun). These four
species, formerly all called /Panopeus/, are small crabs which live
in the mud and are commonly known as mud-crabs. They are abundant
under stones in muddy places, and occur on the Atlantic coast from
Massachusetts Bay to Florida, though they are not commonly met with
north of New Jersey. /Eupanopeus herbstii/ is the largest one of
the group, some of the Southern ones measuring two inches across.
It is found living in mud at low-water mark, or burrowing in banks
near high-tide mark. It is dark olive-brown, the claws broadly
tipped with black. /Eurypanopeus depressus/ is flattened above,
and is smaller than /Neopanopeus texana/, which is somewhat convex
above. The last two are commonly found together and have similar
habits. /Rhithropanopeus harrisii/ lives near high-water mark and
also in salt-marshes, and is comparatively rare. The claws lack the
dark tips of /E. herbstii/, and a distinct groove follows the edge
of the carapace.
FAMILY ~GRAPSIDÆ~
GENUS ^Hemigrapsus^
^H. nudus^ (Mary J. Rathbun), ^Heterograpsus nudus^ (Stimpson);
^H. oregonensis^ (Mary J. Rathbun), ^Heterograpsus oregonensis^
(Stimpson). These two species, commonly called respectively the
/purple shore-crab/ and the /yellow shore-crab/, are the most
abundant species of the California coast. Hundreds may be found
congregated under a single rock. They range from Sitka to Lower
California. /H. oregonensis/ literally swarms in sloughs of salt
or brackish water, and hundreds of uplifted threatening claws
confront the intruder who ventures on these mud-flats when the tide
is out. This species, the yellow shore-crab, has a nearly square
body. The anterior half of the side margins has two rather deep
indentations, [pg282] making two spine-like projections which bend
forward. The four posterior pairs of legs are more or less hairy;
the chelæ are rather large in proportion. The male is about one
inch across and the female is one third less in size. The general
color is yellow. /H. nudus/ is found in the same localities, and
differs from /H. oregonensis/ in being purple in color, with
mottled claws, and in having the denticulations less pronounced
and the walking-feet devoid of hairs. It is also a little larger.
(Plate LXIII.)
GENUS ^Pacygrapsus^
^P. crassipes.^ A species very common on the California coast south
of San Francisco. This crab is similar in general features to the
purple and yellow ones described above, but is considerably larger,
and the carapace is banded with color.
FAMILY ~OCYPODIDÆ~
GENUS ^Ocypoda^
^O. arenaria^, the sand- or ghost-crab. The name /Ocypoda/ means
"swift-footed," and, as it implies, this species is especially
noted for its rapidity of movement. These crabs are the opposite
of the strong-armed, thick-shelled, slow-moving /Cancroidæ/. An
instance is told of a collector having great difficulty to keep up
at full run with one which he chased for a considerable distance
over the sand. They are also dexterous in burrowing, and live in
holes, often three feet deep, dug perpendicularly into the sand.
They wander far from their burrows when the tide is out, and
every little while raise their stalked eyes and stand on tiptoe
to look about. If alarmed, they run with great rapidity to the
nearest burrow, or, if danger is close, press themselves on the
sand until an attempt is made to touch them, when they again dart
away rapidly, and in running hold their bodies high, and double
and dodge so that it is difficult to catch them. /Ocypoda/ is
colored almost exactly like the sand, and this mimicry, together
with its fleetness, makes it interesting to note and difficult
to capture. It inhabits sandy beaches above tide-mark from Long
Island to Brazil, and subsists largely upon the beach-fleas, which
inhabit the same localities. It springs upon them, very much as a
cat catches a mouse. The carapace of this species is almost square
in outline, and on the anterior corners ends in a spine. A small
portion of the carapace folds down like a band between the eyes. On
each side of this band, and extending across the front, are large
grooves for the eye-stalks. The body is about an inch thick; the
first joints of the chelæ are toothed; one chela is a little longer
than the other, and both are coarsely granulated. The other four
pairs of legs are thickly fringed with hairs. (Plate LXIII.)
[Illustration: PLATE LXIII. Hemigrapsus nudus. Hyas araneus. Ocypoda
arenaria. Pugettia gracilis. Libinia dubia. Pitho aculeata.]
[Illustration: /Uca/ (/Gelasimus/) /pugilator/, the fiddler-crab;
male.]
GENUS ^Uca^
^U. minax^ (^Gelasimus minax^), ^U. pugnax^ (^Gelasimus pugnax^),
^U. pugilator^ (^Gelasimus pugilator^), the fiddler-crabs. These
species [pg283] of fiddler-crabs occur on the Atlantic
coast. They congregate in immense numbers, and excavate their
holes in convenient localities above the reach of the tides--on
salt-marshes, far up the estuaries, and along the mouths of rivers,
even where the water is quite fresh. The males have one claw very
largely developed; the other chela is small. The former is likened
to a fiddle, the latter to a bow, and this, together with the
waving motion of the large claw, gives them their popular name.
This comparatively enormous claw is a distinguishing feature by
which they are easily recognized without other description. The
female has claws of small and equal size. These crabs burrow holes
in the mud or sand half an inch to two inches in diameter and a
foot or more in depth. The upper part is nearly perpendicular,
becoming horizontal below, with a chamber at the end. One species,
/U. minax/, constructs an archway over the mouth of its burrow, in
which it sits and surveys the surroundings, but quickly retreats
when danger approaches. The crab makes its burrow by scraping up
the mud or sand and forming it into pellets, which it carries under
the three anterior walking-feet on the under side, using the legs
on the side moving forward, and the fourth one on the other side,
to climb out of the hole. After peering cautiously about, the
crab emerges, and carries its load four or five feet away before
dropping it; then again looks about before quickly running back;
and, finally, turning its stalked eyes, looks in all directions
and suddenly disappears, soon to return with another load. The
burrows cover considerable areas, and the crabs are so abundant
that the marshes and shores sometimes seem to be alive with them.
When alarmed, they lift the large claw and run sideways, after
the manner of all crabs, to their holes, and, as many are likely
to retreat into the most convenient one, the owner often finds
his burrow occupied by other tenants, whom he unceremoniously
proceeds to pull out. /U. minax/ ranges from southern New England
to Florida, and lives on salt-marshes farther away from the sea
than the others, and often where the water is quite fresh. It
is larger than the other species, and can be distinguished by a
red patch at the joints of the legs. It is a vegetarian in diet,
living on small algæ. This is the species which constructs a little
observation-house over the mouth of its burrow. It can live out of
water, and without food, for several days. /U. pugilator/ lives
on sandy and muddy flats and beaches near high-water mark, where
the sand is compact and somewhat sheltered, and ranges from Cape
Cod to Florida. This species, like /U. minax/, is a vegetarian.
/U. pugnax/ is exceedingly abundant on muddy banks and ditches of
salt-marshes, the banks being sometimes completely honeycombed and
undermined by them. It ranges from Cape Cod to Florida. [pg284]
FAMILY ~MAIIDÆ~
The members of this family are known as "spider-crabs." Their bodies
are thick and more or less round in form, narrowing in front to
a long, beak-like projection. The surface is generally rough and
irregular, having tubercles, spines, prickles, and hairs. The legs
are long. These crabs are often covered with seaweeds, hydroids,
and other organisms, which they gather with their long and flexible
chelipeds and place upon their backs, presumably to conceal
themselves from their enemies. They seem to select, instinctively or
with reason, such things as will bear transplanting, sometimes using
sponges and polyps which are not destroyed by being torn apart, and
they also select their dress with reference to its masking uses. A
/Hyas/ covered with bright-colored algæ was seen to remove them and
replace them with sponges, when transferred to the locality of the
latter, where the former did not grow. The animal takes in his claw
the object he has gathered, and first holds it to his mouth, where it
is moistened with a secretion of mucus or cement, and then places it
on his back. If it does not hold, the operation is repeated, often
several times, a new spot on the shell being selected each time. It
has also been found that the coats of these crabs are covered with
hairs which are differently arranged in different genera, some being
hooked, others serrated, etc., and that these aid in holding the
transplanted organisms in place. The crab is sometimes so covered
with these growths as to be entirely concealed beneath them. It is a
sluggish animal, and inhabits shallow water along the whole of the
Atlantic and Pacific coasts.
GENUS ^Libinia^
^L. dubia^, ^L. emarginata^. These two species inhabit the
Atlantic coast, and are found on muddy shores and flats, among
decaying seaweed, in eel-grass, and even beneath the surface of
the mud. They are covered with hairs, and sometimes have planted
on their backs algæ, hydroids, and even barnacles. The legs of /L.
emarginata/ often spread a foot or more. The males are much larger
than the females. The species ranges from Maine to Florida. /L.
dubia/ does not extend north of Cape Cod. It is found more commonly
than /L. emarginata/ in very shallow water [pg285] near shore. It
is not so thickly covered with spines, and has a longer rostrum,
which is also more deeply divided at the end. (Plate LXIII.)
GENUS ^Hyas^
^H. coarctatus^, the toad-crab. This species of spider-crab is
found from Greenland to New Jersey, in shallow as well as in deep
water. Its body resembles strongly, both in form and size, that of
a toad, hence its common name. It forms an important part of the
food of the cod.
^H. lyratus.^ A toad-crab of the Pacific coast, ranging from Bering
Sea to Puget Sound; named from the lyre-shape of its carapace.
^H. araneus.^ A species which especially resembles a toad in its
form. Found off the northern New England coast. (Plate LXIII.)
GENUS ^Loxorhynchus^
^L. crispatus^, the sheep-crab. This crab occurs on the coast of
southern California. The body is thick and about three inches
across the widest portion, and tapers to a long, prominent rostrum.
It is covered with long tubercles and spines and with short,
bristly hairs; the legs are long, the chelipeds stretching fully
two feet.
GENUS ^Pugettia^
^P. gracilis.^ A small spider-crab found on the Pacific coast from
Alaska to Puget Sound. Its body is one half of an inch wide and
[pg286] one inch long, with prominent spines on the sides of the
carapace, which narrows in front into a long beak ending in two
spines. It is red and green above, red beneath. (Plate LXIII.)
GENUS ^Sternorhynchus^
^S. sagittarius.^ This is one of the most delicately formed of the
spider-crabs. The body has narrow longitudinal stripes of light and
dark color. It lives offshore from Cape Hatteras southward.
[Illustration: /Epialtus productus/, the kelp-crab; female.]
GENUS ^Epialtus^
^E. productus^, the kelp-crab. This crab inhabits the coasts of
California and Oregon, and is found among seaweeds on rocks just
below low-water mark. The carapace is smooth, is quadrate in form,
is about two inches long and broad, has two spines on each side,
and has a prominent denticulated rostrum. This is the most common
spider-crab of the Pacific (California) coast. It is olive-green,
thus simulating in color the kelp among which it lives. (See page
285.)
GENUS ^Pitho^
^P. aculeata.^ The carapace has six spines on each side, the
middle two being sometimes partly united; the general outline is
pentagonal; the length about one inch. Quite common on the Florida
coast. (Plate LXIII.)
GENUS ^Lambrus^
[Illustration: /Lambrus pourtalesii./]
^L. pourtalesii^, the long-armed spider-crab. The carapace is
broader than it is long and has three elevations all covered with
spines. The general surface is pitted and granulated; the rostrum
points downward; the chelipeds are very long, the margins armed
with spines; the breadth of the carapace is about one and a half
inches; and the length of the chelipeds is about three and a half
inches. Its range is from Cape Cod to Florida, and it lives among
the rocks. (Plate LXIV.) [pg287]
FAMILY ~CALAPPIDÆ~
GENUS ^Calappa^
^C. flamma^, the box-crab. This singular animal lives on sandy and
muddy bottoms offshore, from North Carolina southward. The carapace
is broad and straight on the posterior side, and is curved on the
anterior side, narrowing to the front. The posterior side has
prominent denticulations. The body is one and a half inches thick,
about four to five inches wide, and two to three inches long.
The chelæ are large, broad, and flattened, and are so arranged
that when flexed they fit closely together across the front. When
folded, and the small legs are withdrawn under the carapace, the
animal is shut up as if in a box, and resembles a shell. When in
danger it closes its doors, as it were, and abandons itself to the
waves, which often carry it ashore. The crested claws resemble the
head of a cock. (Plate LXIV.)
FAMILY ~PINNOTHERIIDÆ~
GENUS ^Pinnotheres^
[Illustration: /Pinnotheres ostreum/, the oyster-crab; male, enlarged
four diameters.]
^P. ostreum^, the oyster-crab. The female of this species lives
in the gill-cavity of the oyster, and is particularly abundant in
oysters from the Chesapeake. The males are seldom seen, and rarely
occur in the oyster, but swim freely about. They are smaller than
the female, have a firmer shell, and are dark brown above, with a
dorsal stripe and two conspicuous spots. The under side of the legs
is whitish. The female is commensal, at least in the adult form,
and its thin, whitish, transparent carapace is tinged with pink.
The species ^P. maculatum^ lives in /Mytilus edulis/ (mussel) and
in the smooth scallop, /Pecten magellanicus/. The oyster-crab is a
true messmate, and its presence in the oyster may be advantageous
in helping to provide food for its host. This crab, like the rest,
holds its eggs in the posterior feet until hatched, when the larvæ
leave the parent and swim about for a while. The females, at the
megalops stage, enter oysters--sometimes two enter the same oyster,
but seldom more than one; there it remains permanently, growing to
the size of an inch or more in diameter, and becomes a degenerate.
The eyes become smaller; the shell never hardens, like its allies
which live in open water; its limbs and chelæ are weak; and it has
no pugnacity, the protection afforded by the oyster doing away with
the need for the common protective features of its kind. /Pinnixa
cylindrica/, a related species, lives in the tubes of large annelid
worms as a commensal. [pg288]
ORDER =STOMATOPODA=
GENUS ^Squilla^
[Illustration: /Squilla empusa/, the mantis-shrimp.]
^S. empusa.^ This animal suggests somewhat the lobster, though very
unlike it. The carapace is much smaller and softer, and leaves
the last three segments of the thorax uncovered. The abdomen is
larger and longer in proportion, while the legs and organs are
quite different. The whole body is depressed, instead of laterally
compressed. It measures from eight to ten inches in length and two
inches in breadth. Instead of chelæ, the last joint of the great
claw has six sharp curved spines, which fit into sockets in a
groove on the second joint. By this singular organ they hold their
prey securely. The abdominal feet carry the gills. The antennal
scales are oblong and fringed with hair. The antennules terminate
in three flagella. The caudal appendages and telson are long,
strong, and armed with spines. This animal lives in burrows in the
mud below low-water mark, forming large, irregular holes, but is
frequently washed ashore. In color it is pale yellowish-green, each
segment being bordered with darker green and edged with yellow. It
is found from Cape Cod to Florida.
ORDER =CUMACEA=
GENUS ^Diastylis^
^D. quadrispinosus.^ Among the minute /Crustacea/ which swim on the
surface of the water, this species, with other small forms, may be
captured by using a muslin net. It is a quarter of an inch or less
in length. It is easily distinguished by its large carapace, the
posterior portion of which is marked off in transverse ridges, the
anterior end running into a sharp-pointed rostrum. It has a long,
slender abdomen, the sections of which [pg289] are distinctly
marked, and it terminates in long, forked spines, which are longer
than the telson. It is found from New Jersey northward.
ORDER =ARTHROSTRACA=
SUBORDER ~AMPHIPODA~
The /Amphipoda/ have a laterally compressed body, with gills on the
thoracic feet and an elongated abdomen. The segments of the thorax
are not united, nor covered by a carapace, but the whole body is
covered with a segmented, polished, flexible cuticle. The three
anterior legs of the abdomen are for swimming-feet, and the posterior
ones are adapted for springing. The antennæ are long and hairy. The
amphipods comprise the beach-fleas and many other small crustaceans
which abound between tide-marks on all beaches. Besides serving in no
small measure as food for fishes, they are scavengers of the beach,
and consume large quantities of waste matter. They are sometimes
used in preparing skeletons for anatomical specimens. Animals to be
skeletonized, being fastened to boards and anchored just below the
surface of the water in sheltered places, are divested of all flesh
in a few hours, and the bones are more completely cleaned than if
prepared by a naturalist.
GENUS ^Orchestia^
[Illustration: /Orchestia agilis/; male.]
^O. agilis^, the beach-flea. These little crustaceans exist in
countless numbers under the masses of sea-wrack on the beach. When
disturbed they jump about with great agility by means of the last
three pairs of abdominal feet, which are adapted to this purpose.
In color the animal is brown and much resembles the decaying
seaweeds among which it lives and upon which it probably feeds. The
antennules are short, the antennæ long, on two long, jointed bases.
The second pair of feet in the males terminate in chelæ. The last
abdominal appendages are stiff and pointed backward. The abdomen is
curved under. The length of /Orchestia/ is half an inch or less.
Some species occur on all beaches. /O. agilis/ ranges from New
Jersey to Greenland.
GENUS ^Talorchestia^
^T. longicornis^ (^Talitrus longicornis^). This species is similar
to Orchestia agilis, but is about an inch long when mature and
of a paler [pg290] color. It jumps like the latter, but not so
strongly. It is found among the weeds and burrowing in the sand
a little below high-water mark. The wet sand is often completely
filled with its holes. It can be distinguished by its very long
antennæ. Another species, ^T. megalophthalma,^ is distinguished by
its shorter antennæ and very large eyes. Both of these species are
grayish in color and closely resemble the sand. Found from Cape Cod
to New Jersey.
GENUS ^Gammarus^
[Illustration: /Gammarus locusta/, the scud.]
^G. locusta.^ The animals of this genus are among the largest of
the amphipods. The males are larger than the females, sometimes
being one and a half inches long. They are abundant under stones
and /Fucus/ at and near low-water mark. Although much larger than
the beach-fleas, they otherwise resemble them. They do not jump
like the former, but move rapidly, lying on the side, and in water
swim with the back downward. Two pairs of the thoracic feet are
chelate, and three pairs are longer than the others. The feet
on the last segments of the abdomen are stiff and turn sharply
back, forming a part of the tail, which is used most effectively
in locomotion. The antennules and antennæ are of about the same
length. Several species of /Gammarus/ occur in the same range, all
having the same general characteristics; some have but one pair of
chelate feet; the antennules are usually shorter than the antennæ;
the females of all the species have no chelate feet. /G. locusta/
ranges from New Jersey to Greenland. The color is generally
reddish- or olive-brown. ^G. annulatus^ is found in the same
places, but usually a little higher up on the beach; it is lighter
in color, and has dark bands with red spots on the sides of the
abdomen. ^G. mucronatus^ occurs from Cape Cod to Florida. ^Melita
nitida^ is a smaller slate-colored amphipod found in some places;
another is ^M[oe]ra levis^, which is whitish, with black eyes.
[Illustration: /Chelura terebrans/, the boring amphipod.]
GENUS ^Chelura^
^C. terebrans^, the boring amphipod. This little crustacean
is associated in its work on submerged timber with the isopod
/Limnoria lignorum/. The excavations of the latter are narrow and
cylindrical, running down into the wood, while /Chelura/ makes
larger burrows in oblique lines near the surface, which give the
wood the appearance of having been plowed. It is very active and
destructive. It feeds upon the wood into which it burrows. Its
color is semi-translucent, thickly mottled above with pink. [pg291]
GENUS ^Caprella^
[Illustration: /Caprella geometrica./]
^C. geometrica.^ These very curious little animals, which are so
slender as to seem like skeletons, are found in abundance clinging
to hydroids, /Polyzoa/, delicate algæ, or eel-grass, or under
stones in tide-pools. They resemble in color, and often in form,
the objects on which they live. Holding on by the posterior feet,
they extend the body out rigidly or sway it about, so that they
resemble little sticks or branches, and often escape detection. In
walking, they bring the hind feet up to the front ones, doubling
the body into a loop like the canker- or measuring-worm. The
appendages on the anterior and posterior ends are furnished with
chelæ and hooks; those of the middle section are rudimentary. This
animal cannot be mistaken for any other. /C. geometrica/ is found
from Cape Cod to North Carolina. Some of the species of this genus
may be found on every coast.
SUBORDER ~ISOPODA~
The isopods have an elongate, flattened, but more or less arched
body, composed of seven thoracic segments and a short abdomen of
six segments. The six segments of the abdomen are smaller than
those of the thorax, and are often more or less united, sometimes
into a single piece with scarcely any trace of division above; but
the number of pairs of appendages is generally six, showing the
composite nature of the apparently simple organ. The last segment,
or telson, is broad and has a pair of modified appendages. The seven
thoracic legs are not all equal, as the name would imply, but vary
greatly in different species. As a rule, they are adapted to walking
or attachment, and in the female some have delicate plates which
form brood-pouches. The swimming-feet fold under the abdomen, and
in some species are inclosed by the first pair, which are large and
plate-like, and form a complete cover for the others. The isopods
are a large and widely distributed order, varying in size, and
are inconspicuous because they cling closely to objects. They are
retiring in habit, though extremely ferocious.
The sow-bugs or pill-bugs, common in gardens, under leaves in the
woods, and under almost any pile of rubbish among decaying vegetable
matter, are a land species of isopods. Other species inhabit [pg292]
ponds and streams of fresh water, and still others are found along
the shores of all oceans, abounding among the marine vegetation
of the shallow waters. Some swim free in the open sea; others are
brought up from the greatest depths. Others, again, are parasites,
and live in the internal organs of fishes and prawns. Sometimes
a prawn is found having what appears like a very swollen throat,
which actually is a little parasitic isopod of the family /Bopyridæ/
attached to its gills.
GENUS ^Cirolana^
[Illustration: /Cirolana concharum./]
^C. concharum.^ The body consists of fourteen segments, the first
being the head, the next seven the thorax, and the last six the
abdomen. On the head are the triangular eyes, the antennules, and
the antennæ, and underneath is the mouth, which is covered by the
maxillipeds. The dorsal surface is more or less rounded. At the
bases of all the segmental thoracic rings excepting the first one
are sutures marking off square, scale-like pieces (/epimera/). The
epimera form a border to the side margins. The legs are attached to
the epimera, which are, in fact, the upper segments of the legs.
The first three pairs of legs have a general resemblance to one
another, and are directed forward. The last four pairs are much
longer and flatter, and are directed backward. The telson, or last
segment, is triangular, and the square or blunt apex is fringed
with hairs. On the ventral surface of the thorax in the adult
females there is a long pouch for the reception and development
of the eggs. This species is usually about one and a half inches
in length, but sometimes is longer. Its color is yellowish, with
a brown edge on the posterior margins of the segments, somewhat
translucent in the thinner parts. It is found from Cape Cod to
South Carolina, swimming about in shallow water, and is especially
abundant in winter.
GENUS ^Limnoria^
[Illustration: /Limnoria lignorum/, the gribble.]
^L. lignorum^, the gribble. This little isopod is very destructive
in its habits, boring into submerged woodwork, like the ship-worm
(Teredo), and doing great damage to the piles of wharves, etc. It
burrows to the depth of half an inch, and completely honeycombs
the surface of the wood, which then scales off or rapidly decays,
and is washed away by the waves. The animal then begins anew,
and in a short time, or at the rate of about an inch a year,
piles diminish in diameter where /Limnoria/ is plentiful, and are
finally destroyed unless protected from these little crustaceans
by a sheathing of metal. Although considered as pests, they have
an economic value not so often recognized, as they attack all
driftwood, and in time entirely destroy floating and water-logged
[pg293] timber, which without their destructive agency might become
serious obstructions to navigation. /Limnoria/ is only the fifth
of an inch in length, and its back is covered with minute hairs,
to which dirt usually adheres. It burrows with its mandibles, or
jaws, which are chisel-like at the ends. Its habitat extends from
a little above to a little below tide-marks throughout the whole
Atlantic coast.
GENUS ^Sphæroma^
^S. quadridentatum.^ The name of the genus to which this species
belongs is derived from the peculiar habit of many of the species
of rolling themselves into a ball when alarmed. The body is so
constructed as to admit of this singular change of shape. The
abdomen turns under, and the last abdominal appendages, together
with the narrow epimera, shut in the legs and cover the ventral
portions with armor. The body, when extended, is an ellipse a
little over a quarter of an inch in length and half that in
breadth. The legs are hairy and adapted to walking. The anterior
abdominal segments are fused into one, but are marked at the sides
with depressed lines. The abdominal feet are plate-like and fringed
with hairs. A slight elevation runs around the margins of the
animal like a border. The color is variable. Some are a uniform
slaty gray; others are marked with a longitudinal patch of color
on the back. It is found from Cape Cod to Florida among algæ or
rocks, and is easily recognized by its habit of rolling itself
into a ball. ^Sphæroma destructor^ is a boring isopod, larger than
/Limnoria/, and is even more destructive, since its holes are
larger; but its range is limited, or, at least, it has so far been
found only in the St. Johns River, Florida.
[Illustration: /Sphæroma quadridentatum./]
GENUS ^Idotea^
[Illustration: /Idotea marina./]
^I. marina^ (Linnæus), ^I. irrorata^ (Edwards). This species is
about one inch long, and is easily recognized by the abdomen, the
first three segments of which are narrow and terminate in acute
teeth, while the other three are fused into one with straight sides
and ending in three teeth, of which the middle one is the longest.
The first pair of abdominal feet are large, long, and plate-like,
covering the other feet and whole under surface of the abdomen like
an operculum. The head is nearly square, the eyes are small, and
the antennæ have long peduncles. The articulations of the thoracic
feet are fringed with hair. The color of this species varies:
sometimes it is light or dark green, or brown with black spots;
again [pg294] it is striped longitudinally with light color.
Sometimes the stripes run transversely in bands or spots. It is
found from New Jersey northward on rocky shores of bays and sounds,
or in eel-grass on sandy shores.
^I. ochotensis.^ A species very similar to the preceding, but a
little larger, found on the Pacific coast.
^I. metallica.^ This species is a little smaller than /I. marina/,
and differs from it in having the end of the telson truncated, or
straight, instead of dentate. The head is nearly square. The body
is broadest in the middle of the thorax; the projecting epimera
give a serrate appearance to the sides. The abdominal feet are
inclosed in the operculum-like scales of the first pair of feet.
Its color is bright blue or green, often with a metallic luster
when seen in the water. It is found swimming free or floating in
masses of seaweeds from Long Island northward and also on the
Pacific coast.
^I. wosnesenskii.^ A common species on the California coast,
about one inch long and dark in color. The abdominal segments are
united and bluntly rounded, and each has a small median tooth. The
abdominal feet are inclosed by the opercular feet. Eggs and young
are carried in a pouch.
GENUS ^Chiridotea^
[Illustration: /Chiridotea cæca./]
^C. cæca.^ This species burrows beneath the surface of the sand,
raising it up into a little ridge, and makes a mound at the end of
the burrow, where it may be found. These trails are common on the
wet sand. It imitates the sand in color, and is about half an inch
in length, with a broad thorax and narrow abdomen terminating in a
point. It is found on the New England coast.
^C. entomon^ (Linnæus). This species of the northern Pacific coast
is from one to three inches long. The head has the appearance of
two lobes, the sides having two rounded ends. The body is broad,
the abdomen narrowing to a pointed end. The last segments of the
abdomen are united, and the abdominal feet are inclosed by the
first pair, which extend over them like an operculum. The epimera
are broad, with acute lateral angles.
CLASS =MERISTOMES=
ORDER =XIPHOSURA=
GENUS ^Limulus^
[Illustration: Under surface of horseshoe-crab, /Limulus polyphemus/:
/a/, abdomen; /c/, cephalothorax; /g/, the first gill-bearing
abdominal appendage; /m/, mouth; /o/, operculum; /p/, telson; /s/,
metastoma; 1-6, cephalothoracic limbs.]
^L. polyphemus^, the horseshoe- or king-crab. This well-known
and curious animal ranges along the Atlantic coast from Maine
to Mexico. [pg295] It lives on sandy and muddy shores below
low-water mark, where it burrows beneath the surface. At the
breeding season--May, June, and July--it comes ashore to deposit
its eggs near high-water mark. The crabs come up the beach in
pairs, the male being the smaller and riding on the back of the
female, holding on by short feet provided with nippers, which
are peculiar to the males. Sometimes the female is accompanied
by several males, each one holding on to the tail of another and
forming a string of animals. After the female has deposited her
eggs in a hole excavated by her for the purpose, the male covers
them with milt, and they then return to the water, leaving the
eggs to be buried in the sand by the action of the waves. The eggs
hatch in July and August, and sometimes the beach is literally
alive with the young crabs, which, however, soon disappear, and
are not seen again until they are well grown. After the spawning
season the adults are not very often seen, but usually their empty
shells, abandoned in moulting, may be found on the shore. The
horseshoe-crab, also called king-crab, is especially interesting
from the fact that it is the last survivor of an otherwise extinct
group of animals. Its relationships with classes which have become
extinct, its nearest relatives being fossils, make it difficult
to classify definitely with existing forms. Formerly it was
regarded as a crustacean; now it is classed by some authors with
the /Arachnida/, along with scorpions and spiders. It has the
characteristics of both groups. There are only two known species of
/Limulus/ in the world; the other, ^Limulus moluccanus^, lives on
the eastern coast of Asia. /L. polyphemus/ often measures a foot in
diameter. The body is composed of three parts. The front portion,
or cephalothorax, is broad and semicircular, with posterior angles
ending in points. Near each side of its dorsal surface is a pair of
large compound eyes covered with thickened cuticle, and near the
center line of the shell, at the base of the first spine, a pair
of small, simple eyes. The second portion is the abdomen, and the
third a long, movable spine attached to the last segment of the
abdomen and between two terminal points of the horn-like covering.
[pg296] On the cephalothorax are seven pairs of appendages. The
first pair are small and lie in front of the mouth; these and
the four following pairs have chelæ, or claws. The sixth pair
have no chelæ, but at the base have a peculiar process termed the
flabellum. These six pairs of appendages surround the mouth, and
have bristles at the base which serve as jaws. The seventh pair of
thoracic appendages are broad plates called the operculum, which
meet and cover the abdominal appendages to a certain extent. The
abdomen has five pairs of appendages, which are plate-like and
resemble the operculum in form and have an upper and an under
piece. On the posterior surfaces of the abdominal feet are large,
leaf-like folds, which are the gills. In front of the first pair
of thoracic legs is a small tubercle supposed to have an olfactory
function. /Limulus/ has a blood-vascular system (the blood being
bluish in color), a nervous and a digestive system. It walks with
the thoracic feet and swims with the abdominal ones. It enters
the sand by pushing in the rounded, anterior end. In moulting the
carapace opens on the front edge. /Limulus/ is edible, its meat
being, it is said, as good as that of the lobster. (Plate LXIV.)
CLASS =PANTOPODA= (Lang)
ORDER =PYCNOGONIDA=
This order of animals, like /Limulus/, has no definitely determined
position in the classification of marine organisms. About one hundred
and fifty species of /Pycnogonida/ have been described, of which
thirty are found on our coast and are commonly known as sea-spiders.
They are found crawling slowly over seaweeds, hydroids, and sponges,
and appear to be all legs, but, like other animals, have a digestive,
a circulatory, and a nervous system. They are devoid of organs of
respiration. The body has a cephalothorax, which bears a conical
suctorial proboscis on the anterior end, and on top a prominence
containing four eyes. It has three pairs of appendages, two pairs
of which are sometimes lacking; then come three free segments and
a rudimentary abdomen. There is a pair of short appendages bearing
claws (chelæ) and four pairs of long walking-legs. The walking-legs
contain a tubular outgrowth of the body, into which the stomach
extends. The egg-sacs are in the legs, and open at the basal joints.
The male is provided with an extra pair of legs, for the purpose of
carrying the eggs after they are deposited by the female. The
[pg297] ovigerous legs are run through sac-like pockets and bent
under the body, and thus the eggs are carried until hatched.
[Illustration: PLATE LXIV. Calappa flamma. Calappa flamma, claws
open, showing form of cockscomb. Lambrus pourtalesii. Limulus
polyphemus.]
GENUS ^Phoxichilidium^
^P. maxillare.^ This species is found on the New England coast
creeping over hydroids and ascidians. It is purple, gray, or brown
in color. Its young take shelter in the cavities of hydroids,
forming galls.
[Illustration: /Phoxichilidium maxillare/, enlarged.]
VII
MOLLUSCA
TABLE SHOWING THE CLASSIFICATION OF THE MOLLUSKS DESCRIBED IN THIS
CHAPTER
Phylum =MOLLUSCA=
Class =AMPHINEURA= (/Bilaterally symmetrical mollusks, having
shell composed of eight plates, or devoid of shell. Including
chitons and their allies/)
Order =POLYPLACOPHORA= (/Shell composed of eight plates/)
Order =APLACOPHORA= (/Devoid of shell/)
Class =GASTEROPODA= (/Unsymmetrical univalve mollusks, usually
spirally coiled. Periwinkles, whelks, snails, etc./)
Order =OPISTHOBRANCHIATA= (/Branchiæ, when present, behind
the heart/)
Suborder =TECTIBRANCHIATA= (/Branchiæ more or less covered
by mantle; shell delicate and often rudimentary/)
Suborder =NUDIBRANCHIATA= (/Devoid of shell and mantle, and
without true branchiæ/)
Order =PROSOBRANCHIATA= (/Branchiæ situated in front of the
heart/)
Suborder =DIATOCARDIA= (/Usually two auricles, two
branchiæ, and two nephridia/)
Suborder =MONOTOCARDIA= (/One auricle, one branchia, one
nephridium/)
Order =PULMONATA= (/Air-breathing mollusks/)
Class =SCAPHOPODA= (/Mollusks without head, eyes, or heart,
with trilobed foot and tubular shell open at both ends. The
tooth-shells/)
Class =PELECYPODA= (/Bilaterally symmetrical, headless, bivalved
mollusks. Mussels, cockles, oysters, etc./)
Order =PROTOBRANCHIATA= (/Gills form a single pair of
plume-like organs, each with two rows of flattened
gill-filaments/)
Order =FILIBRANCHIATA= (/Two pairs of plate-like gills formed
of V-shaped filaments/)
Order =PSEUDOLAMELLIBRANCHIATA= (/Gills plaited so as to form
vertical folds/)
Order =EULAMELLIBRANCHIATA= (/Firm, basket-work gills, the
filaments united by vascular connections/)
Class =CEPHALOPODA= (/Mollusks of high organization, having
a definitely formed head surrounded by tentacles; shell,
when present, usually internal; shell, external in nautili.
Cuttlefishes, squids, octopi, and nautili/)
Subclass =Tetrabranchiata=
Subclass =Dibranchiata=
Order =OCTOPODA=
Order =DECAPODA=
[pg302]
TERMS USED IN DESCRIBING MOLLUSKS
^Abductor muscles^: Muscles which move parts away from the axis.
^Adductor muscles^: Muscles which draw parts together; opposite of
/abductor/.
^Aperture^: Opening of the spiral shell.
^Bilateral symmetry^: Having two equal sides, divided by a central
axis.
^Branchiæ^: Gills, or breathing-organs; organs subservient to
respiration through water. Same as /ctenidia/.
^Buccal mass^: The mouth-parts as a whole; the organ of prehension
and mastication of food; the pharynx: present in all mollusks except
lamellibranchs.
^Canal^: A narrow prolongation of the aperture of a spiral shell.
^Carinated^: Ridged as if keeled; having a keel.
^Cinereous^: Ash-gray; having the color of wood-ashes.
^Cirri^, plural of ^Cirrus^: Filamentous appendages.
^Columella^: An upright pillar in the center of most of the univalve
shells, round which the whorls are convoluted.
^Concrescent^: Growing together; uniting.
^Cordate^: Heart-shaped.
^Costæ^, plural of ^Costa^: Ridges of a shell.
^Crenulated^: Having a series of notches; marked as with notches, as
the indented margin of a shell.
^Crystalline style^: A transparent gelatinous substance of unknown
function, which fills, at times, the stomach-parts of certain
mollusks.
^Ctenidia^, plural of ^Ctenidium^: Gills, or breathing-organs,
adapted to water-respiration. [pg303]
^Decussated^: Crossed; intersected.
^Dextral^: Having the aperture on the right side of the shell when
the apex is upward.
^Epidermis^: The horny coating or outer skin of some shells.
^Foot^: The ventral surface of the body on which the animal rests or
moves.
^Fossette^: A little hollow or pit.
^Fuscous^: Brown tinged with gray; swarthy.
^Fusiform^: Tapering both ways from the middle.
^Lamelliform^: Lamellate in structure; disposed in leaf-like layers.
^Lingual ribbon^: The chitinous band of teeth, or rasp, borne upon
the odontophore; the radula.
^Lunule^: An impressed area just below the beaks of bivalve shells.
^Mantle^: A fleshy or membranous outgrowth of the outer body-wall;
also called /pallium/.
^Mantle cavity^: The space between the mantle and the body.
^Monomyarian^: Having one adductor muscle, as an oyster.
^Nephridium^: The renal organ of mollusks, corresponding to kidneys
in vertebrates.
^Node^: A knob or protuberance; also a notch in the margin.
^Odon´tophore^: The lingual ribbon bearing chitinous teeth.
^Oper´culum^: A horny or shelly plate which serves to close the
aperture of the shell when the animal is retracted.
^Osphra´dia^, plural of ^Osphradium^: Olfactory or water-testing
organs.
^Otocyst^: The cavity, or cyst, which contains the essential parts of
an organ of hearing.
^Pallial line^: The impression or mark made by the mantle, or
pallium, on the inner surface of a bivalve shell.
^Pallial sinus^: A notch or recess of the pallial line; the scar of
the siphon.
^Papillaceous^: Warty; studded with bosses; having excrescences.
^Perios´tracum^: Same as /epidermis/.
^Per´istome^: In zoölogy, mouth-parts in general; in conchology, the
margin of the aperture of the shell. [pg304]
^Porcelanous^: Resembling porcelain.
^Rad´ula^: Same as /lingual ribbon/.
^Reticulated^: Having distinct lines or veins crossing like a
network; covered with netted lines.
^Sculpture^: Elevated or impressed marks on the surface; markings
resulting from irregularity of surface; tracery.
^Sinistral^: Having the aperture of the shell at the left; opposite
of /dextral/.
^Sinuate^: Curved in and out; wavy.
^Siphon^: A tubular fold, or prolongation of the mantle forming a
tube.
^Spire^: All the whorls of a spiral univalve, above the first large
body-whorl.
^Suture^: The line of junction of the successive whorls of a univalve
shell, or the line of closure of the opposite valves of a bivalve
shell.
^Teeth^: Tooth-like projections on the hinge of a bivalve shell.
^Testaceous^: Having a hard shell, as distinguished from crustaceous,
or soft-shelled.
^Turbinate^: Shaped like a whipping-top; whorled from a broad base to
an apex.
^Umbilicus^: A central, navel-like depression in the body-whorl; a
circular, more or less central pit or hollow.
^Umbo^: The beak of a bivalve shell; the protuberance of each valve
above the hinge.
^Varices^, plural of ^Varix^: Raised marks on the shell denoting a
former position of the lip of the aperture, and indicating periods of
rest.
^Varicose^: Having prominent and tortuous formations on the shell.
^Ventricose^: Having the whorls of the shell swollen or strongly
convex.
^Whorl^: One of the turns of a spiral shell. /Body-whorl/, the last
whorl.
[pg305]
MOLLUSKS
We now come to another large and important group of animals, with
characters so peculiar to itself and differing so radically from
those which distinguish any other class of living creatures, that
it may be said to occupy almost a unique position in the animal
kingdom. Recent investigations have demonstrated that the larval
form of mollusks presents some remarkable points of similarity to
the embryonic forms of the /Annelida/ and to the larvæ of some other
classes of lower organisms. This discovery is one of the triumphs
of embryology in its patient search for that connecting-thread that
weaves together all the varying forms of animal life. Aside from
these subtle evidences of relationship revealed by the microscope,
the mollusks appear to occupy a position of considerable isolation in
the biological world.
As accepted by zoölogists to-day, this phylum is but the remnant of
its former self. Aristotle considered all creatures with a testaceous
covering to belong to a single family, and those later patriarchs of
biology, Linnæus, Cuvier, and Lamarck, extended the group to include
the greater part of all the marine invertebrate animals. Little by
little the phylum has been shorn of orders and classes. First, the
worms and the /Echinodermata/ were separated into distinct phyla;
then the barnacles were discovered to be crustaceans, and were
accordingly removed from their position as "multivalves" under the
/Mollusca/; then the tunicates, or ascidians, were found, through the
critical examination of their larval stage, to be merely masquerading
as mollusks; and lastly, the brachiopods have been somewhat
reluctantly removed from their old position with the mollusks and
given the [pg306] distinction of a phylum almost exclusively to
themselves: they retain their old associations only in the name of
/Molluscoida/.
With some exceptions, all mollusks secrete from their outer skin, or
mantle fold, a calcareous protective covering, or shell. This may be
either "univalve" or "bivalve" according as it consists of one or two
pieces. This phylum includes all the sea-shells which are so commonly
found along every ocean beach, in the tide-pools, on rocks at low
tide, in estuaries, and, indeed, wherever sea-water is present. The
phylum also includes, as one of its large suborders, all the snails
and slugs that are to be found crawling upon the land. These are true
mollusks, which differ essentially from their marine brethren only in
that they breathe by means of a pulmonary sac or lung instead of by
gills. There are also many genera and species of mollusks that find
their habitat only in the fresh water of rivers, lakes, or ponds;
curiously enough, many of these fresh-water forms, like the purely
terrestrial snails and slugs, are air-breathers, possessing no gills
whatever, and are consequently obliged to make periodic visits to
the surface of the water to obtain their necessary supply of oxygen.
There are also numerous forms of mollusks that are entirely deprived
of a shell covering; and, again, there are intermediate types
between these two extremes that produce only more or less developed
rudimentary shells. Notwithstanding these variations in the matter
of a shell covering,--an important consideration in this phylum,--by
reason of their anatomical features these "naked" forms are mollusks
quite as much as are those that secrete the most highly developed
tests.