PART II

MARINE INVERTEBRATES

I

PORIFERA

(SPONGES)

TABLE SHOWING THE CLASSIFICATION OF THE SPONGES DESCRIBED IN THIS

CHAPTER

Phylum and Class =PORIFERA=

Subclass =Calcarea=

Order =HETEROC[OE]LA=

Family ~SYCONIDÆ~

Genera Species

^Grantia^ ^G. ciliata^

^Leucosolenia^ ^L. botryoides^

Subclass =Non-Calcarea=

Order =CHONDROSPONGIÆ=

Family ~SUBERITIDÆ~

^Suberites^ ^S. compacta^

^Polymastia^ ^P. robusta^

^Cliona^ ^C. sulphurea^

Order =CORNACUSPONGIÆ=

Family ~DESMACIDONIDÆ~

^Esperiopsis^ ^E. quatsinoensis^

^Microciona^ ^M. prolifera^

Family ~HETERORRHAPHIDÆ~

^Tedania^

Family ~HOMORRHAPHIDÆ~

Genera Species

^Halichondria^ ^H. panicea^

Family ~SPONGIDÆ~ Subfamily ~EUSPONGINÆ~

^Chalinopsilla^ ^C. oculata^

^C. arbuscula^

^Euspongia^ ^E. officinalis^

Var. ^adriatica^

Var. ^mollissima^

Var. ^rotunda^

Var. ^dura^

^Hippospongia^ ^H. equina^

Var. ^cerebriformis^

Var. ^meandriformis^

Var. ^elastica^

^H. canaliculata^

Var. ^gossypina^

Var. ^flabellum^

Family ~SPONGIDÆ~ Subfamily ~STELOSPONGINÆ~

^Hircinia^ ^H. campana^

[pg101]

SPONGES

There are many animals which consist of but one cell. These are

called /Protozoa/, and comprise the /Infusoria/ and other microscopic

organisms. The animals next higher in the scale are /Metazoa/, or

multicellular animals, and the first group of this subdivision is

=Porifera=, the sponges, the lowest of the many-celled animals.

For a long time sponges occupied a disputed ground between the animal

and vegetable kingdoms. Aristotle was the first to point out that a

sponge is not a plant. The assertion was doubted and combated, but at

last the animal nature of the sponge was established. Sponges were

then believed to be colonies of one-celled animals, but finally it

was decided that they were individuals with cells of different kinds

that performed functions analogous to those of higher organisms.

The sponge, as commonly seen, is only the skeleton or framework, so

to speak, of the living animal. In its natural state it is a very

different-looking object. Its entire surface is covered with a thin

slimy skin, usually of a dark color, which is perforated with holes

corresponding to the apertures of the canals. The organic portion

of the sponge is a soft, jelly-like substance composed of three

layers--the external (/ectoderm/), the internal (/endoderm/), and

the middle (/mesoderm/). The external layer is composed of flat

cells. The endoderm has cylindrical cells, each one of which has a

flagellate hair. The main mass of the body, the mesoderm or middle

layer, is made up of cells having various functions, some being

concerned in the formation of framework, some in digestion, and some

in reproduction.

The framework is secreted in the mesoderm, and in different

[pg102] genera consists respectively of a horny or silicious or

calcareous substance, or of the first two of these substances

combined. The sponge of commerce has the first kind and is composed

entirely of exceedingly fine flexible fibers of a horny substance

called /spongin/. In other species the spongin is intermixed with

spicules of silica, or of carbonate of lime, in various shapes.

In the sponges, so much valued as curiosities, called "Venus's

flower-basket" and "glass-rope sponge," the framework is composed of

silicious spicules alone.

[Illustration: Various forms of sponge-spicules.]

The spicules have a great variety of shapes, being rod-like, knobbed,

three-pointed, six-pointed, anchor-like, etc., and are a feature in

the classification of sponges.

[Illustration: To illustrate choanocytes (/Ch/): section of a

calcareous sponge. /Ect/, ectoderm; /Mes/, mesoderm; /N/, calcareous

spicule; /Eiz/, ovum.]

The sponge is traversed throughout by a canal system, consisting of a

series of tubes through which water circulates, carrying air and food

to the animal. The exterior of the sponge has numerous small pores

and a comparatively few large openings. The fine pores are inhalent,

taking in and straining the water of its coarser floating material,

and then passing it through perforations in their sides into sacs

lined with peculiar cylindrical cells having flagellate hairs, each

hair having a collar at its base. These cells, called /choanocytes/,

resemble independent animals of the /Protozoa/, known as /flagellate

Infusoria/ or /Choanoflagellata/. [pg103] They take in and digest

food and eject excrement from the area inclosed by the collar. The

cilia (hairs) by their constant movement create currents which keep

the water in motion. Water, then, is taken through the pores into

the first or incurrent canals; thence it is passed into the ciliated

chambers, and thence into the excurrent canals, and out through large

passages terminating in large openings called /oscula/, or craters.

The canal systems vary. In some species they become quite complex.

[Illustration: Canal system of /Sycon gelatinosum/. Transverse

section through the wall of a cylinder (parallel with the course of

the canals), showing one incurrent canal (/IC/) and one radial (/R/)

throughout their length; /sp/, triradiate spicules; /sp´/, oxeate

spicules of dermal cortex (/dc/); /sp´´/, tetraradiate spicules

of gastral cortex (/gc/); /ec/, ectoderm; /en/, endoderm; /pm/,

pore-membrane; /pp/, prosopyle; /ap/, apopyle; /di/, diaphragm;

/exc/, excurrent passage; /PG/, paragastric cavity; /em/, early

embryo; /em´/, late embryo. (The arrows indicate the course of the

water through the sponge.)]

Sponges vary greatly in shape, size, color, surface, rigidity,

canal systems, and skeleton. They are cake-shaped, tubular,

digitate, palmate, cup-shaped, vase-shaped, cone-shaped, spherical,

hemispherical, pedunculate, etc., their shapes depending upon whether

their growth is uniform or is excessive in a horizontal or in a

vertical direction. When they grow evenly in both directions massive

uniform shapes arise. If lateral growth predominates, broad, low,

and incrusting shapes result. When there is an excess of vertical

growth the forms are digitate; [pg104] but if vertical growth is not

greatly in excess and is restricted to the marginal part, cup-shaped

forms result, and tubular forms when lateral growth is particularly

restricted. In some varieties tubular masses coalesce; sometimes flat

forms unite in intricate compressed folds. Differences in rapidity of

vertical growth make undulations more or less marked, producing lobes

and protuberances. Sometimes narrow vertical growth is retarded and

horizontal growth predominates, forming various shapes on apparent

stems.

Many of the horny sponges are colored, in shades of yellow, brown,

red, and violet; some are black.

Sponges are divided into two classes, the =Calcarea= and

=Non-Calcarea=. The former have calcareous skeletons, which make them

hard and rigid; the latter have skeletons of spongin-fiber or of

silicious spicules, or of the two combined.

All sponges, with the exception of one family (the /Spongillidæ/,

which live in fresh water), are inhabitants of the sea, and live at

various depths. The sponges of commerce belong to the /Non-Calcarea/

and are all confined to the genus /Spongia/. In this genus the

skeleton is more or less flexible, being composed of spongin. They

are shallow-water species, are confined to seas where the waters are

of comparatively uniform high temperature, and flourish best when

protected by reefs and islands.

There are fisheries for sponges in the waters of the West Indies, the

Bahamas, on the southern and western coasts of Florida, and in the

Mediterranean and Red seas. Those of the Mediterranean surpass in

quality the sponges of our coasts.

Five species of commercial sponges are taken from Florida waters.

They are graded by the trade in the order of their importance, as the

"sheepswool," "yellow," "grass," "velvet," and "glove." The fishing

for sponges is done from small boats, two persons manning each boat.

One man sculls, while the other, using a water-glass, scans the

bottom. The water-glass is a box with a pane of glass on the bottom.

If the glass is held below the surface and the face is placed in

the box, the observer is enabled to see with some distinctness the

bottom at a considerable depth [pg105] in these clear waters. The

sponges are dragged up by hooks--a primitive method which restricts

the fishing to shallow water, the fishing here being in water not

deeper than thirty feet, but usually three to twenty feet. The

sponges are "killed" by being exposed on the beach for several days;

they are then placed in "crawls," or pens, where they are washed by

the action of the waves for about a week; then, if clean, they are

dried, assorted, strung on cords, pressed and baled for shipment. The

sponge-fisheries are of considerable value, and much attention is

being given to the subject of artificial propagation. It is thought

that such beds could be subjected to the regulations which govern

oyster-beds. Already the planting of sponges has been shown to be

practicable. The living sponge is cut to pieces, and the cuttings

are placed in favorable localities. Pieces planted in Florida waters

attain a marketable size in one year.

Sponges reproduce by eggs formed in the mesoderm. The eggs escape as

ciliated spheres and swim about until they find a place on which to

attach themselves. As soon as they become fixed they grow with much

rapidity into mature individuals.

Some species seem to prefer association with other animals and live

as commensals with crabs. The crab /Dromia/ is always concealed under

a sponge, which grows upon its back. Spider-crabs are often overgrown

with sponges as well as seaweeds. In this case, however, the crab

finds and plants the sponge himself. /Aplysella violacea/ overgrows

worm-tubes. Many sponges afford shelter to numerous small animals

which bore into their bodies for protection, no animal seeming to

feed upon the sponge.

Sponges may be found in tide-pools, on the under side of stones,

on seaweeds, and so on. A small bright-red incrusting sponge with

irregular lobe-like branches is common on the New England coast; a

thin yellow incrusting sponge also is found on the under side of

stones. /Grantia ciliata/, a small urn-shaped species, having a large

aperture at the summit, is found in tide-pools.

Perhaps the most singular in habit of any sponge is /Cliona

sulphurea/, the boring-sponge, a common species found from Cape

Cod to South Carolina and abundant in Long Island Sound. It

[pg106] is bright sulphur-yellow in color, grows in irregular

masses of considerable size and fine texture, and has low wart-like

prominences. It lives on shells spreading over both surfaces, at

first forming little burrows, but eventually penetrating the shell in

every direction, honeycombing and at last completely destroying it

by absorption. Sometimes it settles upon living shells and greatly

irritates the animal, which constantly secretes new lime to cover the

perforations in its shell.

These sponges are an important factor in the economy of the sea, as

they disintegrate dead shells, which would otherwise accumulate in

vast quantities.

SUBCLASS =CALCAREA=

GENUS ^Grantia^

^G. ciliata.^ Small, urn-shaped or oval, with large aperture at the

summit, surrounded by a circle of projecting spicules. It is found

in tide-pools and on piles of wharves from Rhode Island northward.

GENUS ^Leucosolenia^

^L. botryoides.^ Tubular, branched. Occurs in the same places as

/Grantia ciliata/.

SUBCLASS =NON-CALCAREA=

GENUS ^Suberites^

^S. compacta.^ Elongated, compressed masses, sometimes in several

lobes; attached by one edge; texture fine, firm, compact; surface

smooth; color bright yellow. It grows on sandy bottoms, and is

common in shallow water south of Cape Cod. (Plate XXXVIII.)

GENUS ^Polymastia^

^P. robusta.^ When young it forms yellowish-white incrustations

over shells and stones; later it grows into long, slender, round,

tapering, finger-like projections. Found on the northern New

England coasts in deep water.

GENUS ^Cliona^

^C. sulphurea^, the boring-sponge. Irregular massive form of firm

texture; surface covered with scattered low wart-like prominences

about one eighth of an inch in diameter; bright sulphur-yellow. It

destroys, by absorption, vast quantities of dead shells.

[Illustration: PLATE XXXVIII. Halichondria panicea. Suberites

compacta. Hircinia campana. Esperiopsis quatsinoensis (found on the

sea-beaches of Alaska).]

[Illustration: PLATE XXXIX. Microciona prolifera. Chalinopsilla

arbuscula. Chalinopsilla imitans. Euspongia officinalis, var. tuba.

Chalinopsilla oculata.]

GENUS ^Microciona^

^M. prolifera.^ When young this species forms bright-red

incrustations over shells and stones; later it rises into irregular

lobes and tubular prominences. When fully developed it is profusely

branched in a forking manner. The branches are more or less

flattened, and often are palmate at the ends. It grows in clusters

six inches in diameter, of a dark orange-red color. When dry it is

grayish-brown, brittle, and bristly. It is found from Cape Cod to

South Carolina, and is abundant in Long Island Sound. (Plate XXXIX.)

GENUS ^Tedania^

Irregular, uneven, pale-yellow masses spreading over seaweeds; oscula

scattered irregularly over the surface; texture close.

GENUS ^Halichondria^

^H. panicea^, crumb-of-bread sponge. It resembles the crumb of

bread, and is found cast up on all beaches. (Plate XXXVIII.)

GENUS ^Chalinopsilla^

^C. oculata^, the finger-sponge. Stem stout, more or less

flattened, dividing at the upper end into branches which vary in

form and thickness, being finger-like or more or less compressed

lobes; oscula scattered over the smooth, undulating surface;

texture rather hard, but delicate; color, when living, dull

orange-red; when the animal matter is removed, white. The species

is found in shallow and deep water from New York to Labrador.

Common in Massachusetts Bay. (Plate XXXIX.)

^C. arbuscula.^ Profusely branched in a forking manner from close

to the base; branches slender; clusters six to eight inches high

and about the same in breadth; color buff or gray when living,

yellowish-white when free from animal matter; texture finer and

more delicate than that of /C. oculata/. It is found in shallow

water from Cape Cod to North Carolina, and is abundant in Long

Island Sound. (Plate XXXIX.)

GENUS ^Euspongia^

^E. officinalis.^ This is one of the commercial sponges and is

known as the "glove-sponge." It is the one of least marketable

value, having inferior elasticity and becoming brittle with

age; yet a Mediterranean sponge of the same species, variety

/adriatica/, is of the finest quality and greatest value. This

singular fact demonstrates that the quality of sponges depends

largely upon physical conditions. /E. officinalis/ has an average

height of five to six inches. It grows on rocky bottoms in shallow

water on the east coast of Florida. This species has a number of

varieties of various forms; some are dome-shaped, others tubular,

rotund, flabellate, etc. The surface is covered with fine tufts

and is generally free from ridges. On the sides are numerous small

apertures, [pg108] and one or more large oscula occur on top. The

color of the living sponge is black. (Plates XXXIX, XL.)

^E. officinalis^, variety ^adriatica^. More or less globose;

sometimes attached by a broad base, sometimes by a short stem;

latter form more or less club-shaped; oscula scattered over upper

surface. Found in the West Indies and the Mediterranean. (Plate XL.)

^E. officinalis^, variety ^mollissima^, the Levant toilet-sponge.

Generally cup-shaped; oscula on inner side of cup or on upper flat

surface; very soft and elastic.

^E. officinalis^, variety ^rotunda^. Usually massive; attached by a

broad base; sides vertical; oscula large and conspicuous on top, or

small in longitudinal rows on the sides. In the young this variety

may have a conical form with only one orifice, but later it has

several oscula. Its rotundity of form increases with the number of

large orifices, but in the adult stages the form varies, some being

conical, while others have the top divided into radiating ridges.

^E. officinalis^, variety ^dura^. Irregular, massive, horizontally

expanded, with conical process on upper surface.

GENUS ^Hippospongia^

^H. equina.^ Some of the sponges of this species are massive,

spherical, and attached by a small base; others are horizontally

expanded or cake-shaped; some have a depression in the upper

surface and become cup-shaped.

^H. equina^, variety ^cerebriformis^. Massive, circular,

cake-shaped, often depressed in the center, producing a cup-shape,

attached by broad base; surface broken up by parallel longitudinal

ridges having many tufts. Cup-shaped forms predominate, and have

a more or less rough surface. This is one of the species known as

grass-sponges.

^H. equina^, variety ^meandriformis^, the velvet sponge. The

surface of this variety has a protruding flattened cushion of fiber

which slightly resembles the convolutions of the brain-coral.

Sometimes these cushions are extended into long pencils. The oscula

are large and ragged on the edges; the shape is irregular. The

average size is seven to eight inches in diameter. (Plate XL.)

^H. equina^, variety ^elastica^ (variety ^agaricina^, Hyatt), the

yellow sponge. This is the second grade of commercial sponge,

corresponding to the Zimocca sponge of the Mediterranean. It is

found growing with the "sheepswool" in a depth of two to twenty

feet, and is abundant. It is massive and cake-shaped. The whole

surface is a network covered with numerous small, fine cones.

(Plate XL.)

The variety ^dura^ is classed with this species, which it resembles

in appearance, though it is harder in texture.

^H. canaliculata.^ Massive, frondose; more or less horizontally

expanded; bears finger-like processes of varying development on the

upper surface.

^H. canaliculata^, variety ^gossypina^, the sheepswool sponge. This

is the highest grade of the commercial bath-sponge. It is called

"sheepswool" because, perhaps, of its irregular shaggy surface. It

is covered with tufts, the larger oscula occupying the intervening

depressions.

[Illustration: PLATE XL. Euspongia officinalis, var. adriatica.

Hippospongia equina, var. meandriformis. Hippospongia canaliculata,

var. gossypina. Hippospongia equina, var. elastica. Euspongia

officinalis.]

Sometimes these are very numerous, the whole interior being

cavernous; again, the structure is more dense, with fewer large

openings and more of the small ones between the tufts; again, the

depressions are filled up so that the surface has fewer tufts.

When living, the color is shining black. This is the best sponge

found on the American coast, and although of coarser texture than

the best Mediterranean sponges, it is more durable and quite as

elastic. (Plate XL.)

^H. canaliculata^, variety ^flabellum^ (^Spongia graminea^, Hyatt).

This is one of the species of sponges of the third commercial

grade, which bear the trade-name of "grass-sponge." The shape is

cone-like, with either a flat or a funnel-shaped top. The oscula

are on the upper surface. The sides are fluted with deep furrows

which contain the small incurrent apertures.

GENUS ^Hircinia^

^H. campana.^ The normal variety is vase-shaped, but the species

varies greatly in form. Some varieties have branches. When living,

its color is black. It is found at Key West in four to forty feet

depth. (Plate XXXVIII.)

II

C[OE]LENTERATA

(POLYPS)

Phylum

=C[OE]LENTERATA=

Classes

=HYDROZOA=

(/Zoöphytes, small Jellyfishes, and a few Corals/)

=SCYPHOZOA=

(/Large Jellyfishes/)

=ACTINOZOA=

(/Sea-anemones and most of the Stony Corals/)

=CTENOPHORA=

(/Comb-jellies/)

C[OE]LENTERATA

The animals included in the phylum =C[oe]lenterata= were once all

called /zoöphytes/, or animal plants, because of their resemblance

to vegetable forms. The name /C[oe]lenterata/ is derived from two

Greek words meaning "hollow" and "intestine," and it describes the

anatomical structure of each member of the group. They are commonly

known as polyps. In the simplest forms the parts which perform the

different functions cannot be distinguished one from the other, and

even in higher forms there is but little differentiation. Shakspere's

description of old age applies to them: "Sans teeth, sans eyes, sans

taste, sans everything."

Nevertheless, this very low order of animals has, like the

higher orders, such a diversity of form and habit as to require

classification. Some of them are stationary, and of these some branch

like plants; some move about by the aid of tentacles, some move by

means of vibrating cilia, and others move by the contraction and

expansion of the soft body.

Cuvier included them in his /Radiata/, a class comprising all the

animals whose parts diverge or radiate from a central axis. Recent

classification has divided the radiate animals into several classes.

This arrangement of parts is obviously quite different from that

of bilateral symmetry, or the disposal of parts on each side of a

longitudinal axis. The type of radiate structure is shown in polyps.

The body is a sac, in the center of which is another sac or axis.

This is the digestive cavity. Vertical partitions extend from the

central to the outer sac, forming distinct [pg114] divisions or

chambers. The number of divisions varies with the different species

and also with the age of the animal. Other partitions start from the

outer sac, and extend toward the central axis, but do not unite with

it. These partitions, called /mesenteries/, are always in definite

multiples, varying in different species, new divisions growing

between the first partitions in regular order. On the inner edge

of these partitions the eggs of the animal are formed, which, when

mature, drop into the chambers and pass through openings into the

inner sac, or digestive cavity, and out of the mouth into the water.

[Illustration: Diagram of radiate structure.]

The animals are classed according as the eggs are formed on all

or on special partitions, those being of the highest order where

a limitation and constancy of function is maintained. The upper

surface of the body has hollow tentacles, each one of which opens

into one of the chambers and extends outward. All parts of the animal

communicate, and whatever enters the mouth circulates through the

whole structure; and when assimilation is completed the residue

returns by the same road and is expelled through the mouth. This

structure is common to all polyps; but there are great differences

in their texture, some being soft and some horny, while others

deposit a calcareous skeleton (corals). Some grow in colonies, like

the hydroids and corals, and are stationary, others are free and

independent; some have but few, others have many tentacles; and they

differ widely in size, form, and color.

Hydroids, sea-anemones, corals, sea-fans, starfishes, and sea-urchins

are different examples of the radiate structure. They are not,

however, all of them polyps.

The /C[oe]lenterata/ are divided into four classes: =Hydrozoa=, which

include the colonies of zoöphytes which resemble seaweeds, the small

jellyfishes which are born of these colonies, and the /millepores/,

which are colonies of zoöphytes which secrete a stony instead of a

horny skeleton, yet differ in some respects from other [pg115] stony

corals; =Scyphozoa=, large jellyfishes, many of which do not have the

double form of development; =Actinozoa=, the sea-anemones and the

different forms of stony corals, including sea-fans, sea-pens, etc.;

=Ctenophora=, the jellyfishes commonly known as comb-jellies. [pg116]

TABLE SHOWING THE CLASSIFICATION OF THE HYDROZOA DESCRIBED IN THIS

CHAPTER

Class =HYDROZOA=

Order =LEPTOLINIÆ= (/Branched colonies or shrub-like communities of

hydroids; some permanently fixed, others liberate swimming-bells/)

Suborder =ANTHOMEDUSÆ= (/Zoöids not covered by protective sheath;

umbrella of medusæ strongly arched; egg-sacs in manubrium/)

Division TUBULARIANS (/Without polyp-cups/)

Genera and Species

^Clava leptostyla^

^Hydractinia polyclina^

^Coryne mirabilis^

^Sarsia^

^Eudendrium ramosum^

^Tubularia indivisa^

^T. Couthouyi^

^Parypha crocea^

^Corymorpha pendula^

^Hybocodon prolifer^

^Pennaria tiarella^

^P. gibbosa^

^Bougainvillea superciliaris^

Suborder =LEPTOMEDUSÆ= (/Zoöids covered with cup-like sheaths;

umbrella of medusæ thin and not very convex; egg-sacs in line

of radial canals/)

Division CAMPANULARIANS (/Polyp-cups stalked/)

Genera and Species

^Obelia commissuralis^

^Eucope diaphana^

^Oceania languida^

^Clytia poterium^

^C. bicophora^

Division SERTULARIANS (/Polyp-cups sessile/)

^Sertularia pumila^

^S. argentea^

^S. cupressina^

Division PLUMULARIANS (/Polyp-cups on one side of branches

only/)

^Aglaophemia struthioides^

^Plumularia falcata^

Family =GERYONOPSIDÆ=

^Tima formosa^

Family =ÆQUOREIDÆ=

^Zygodactyla groenlandica^

Order =TRACHYLINÆ= (/No fixed zoöphyte stage; always

free-swimming medusæ/)

Suborder =TRACHYMEDUSÆ= (/Tentacles spring from margin of

umbrella; manubrium long; gonads in connection with radial

canals/)

Genera and Species

^Trachynema digitale^

Suborder =NARCOMEDUSÆ= (/Tentacles spring from midway between

summit and margin of umbrella; manubrium short; gonads in

connection with manubrium/)

Order =HYDROCORALLINA= (/Skeleton of carbonate of lime/)

^Millepora alcicornis^

Order =SIPHONOPHORA= (/Pelagic free-swimming colonies; exhibit

extreme polymorphism of zoöids/)

^Nanomia cara^

^Physalia arethusa^

^Vellela limbosa^

TERMS USED IN DESCRIBING HYDROIDS

^C[oe]nosarc^ ("common flesh"): The fleshy axis, or organized living

bond, by which the zoöids are organically united to one another. It

consists of three layers: ectoderm, endoderm, and mesoderm.

^Ectoderm^ ("outside skin"): The outside one of the three organized

layers of which every hydroid is composed.

^Endoderm^ ("inside skin"): The innermost layer.

^Gonangium^ ("seed-vessel"): The external horny receptacle within

which the gonophores are developed.

^Gonophore^ ("seed-bearing"): A generative zoöid.

^Hydranth^ ("water flower"): A nutritive zoöid.

^Hydrorhiza^ ("water-root"): The part of the colony which fixes it to

other bodies, like a root.

^Hydrosoma^ ("water-body"): The entire hydroid colony.

^Hydrotheca^ ("water-receptacle"): The cup-like, horny receptacle

which protects the hydranth.

^Mesoderm^ ("middle skin"): A layer which lies between the ectoderm

and the endoderm.

^Nematophore^ ("thread-bearing"): The name of peculiar bodies

developed in certain genera from definite points; characteristic of

plumularians.

^Perisarc^ ("around flesh"): The transparent, chitinous shell, or

unorganized outer membrane of horny consistency, which covers to a

greater or less extent the soft parts of the colony.

^Zoöid^ ("animal form"): One of the animals which form the colony.

[pg119]

CLASS =HYDROZOA=

SEAWEED-LIKE ZOÖPHYTES AND SMALL JELLYFISHES

The hydroids have been called the nurses of jellyfishes. From casual

observation these two forms would not be associated together, for the

shrub-like organisms, which so much resemble plants that they are

often collected and preserved as seaweeds, suggest only vegetable

life. Examined with a glass, however, they disclose their animal

nature. Along the stems, arranged in various ways, are small cups,

from which protrude the numerous moving tentacles of the little

polyps living within them.

/Hydroids are colonies of associated animals living a communal life./

The multitude of individuals composing the colony are invested with

a horny covering, the /perisarc/, which in some genera assumes a

tree-like form. Through these stems and branches runs a fleshy tube,

a thread of animal substance, which connects in one living whole

the zoöids, or individuals of the community. There is division of

labor, as in other communities: some of the zoöids obtain the food

for the colony, and have tentacles around their open mouths; others

have no mouths, but reproduce the species, and at certain stages of

development liberate swimming-bells, or small jellyfishes (medusæ).

The typical hydroid colony is attached by a kind of creeping stem

from which arises a vertical axis, which gives off short lateral,

alternate branches bearing zoöids at their ends. There is often more

complex branching. The zoöids in certain genera (tubularians) are

uncovered; in others (sertularians) they are incased in a glassy,

cup-like, horny sheath.

Three kinds of zoöids, polyps, or hydranths--as they are

indiscriminately called--are attached to the stem. Those having

an [pg120] open end and a crown of tentacles are the nutritive

individuals. Small, club-like dilations are immature zoöids. The

/blastostyles/, or reproductive zoöids, are long, cylindrical,

mouthless, and covered. At maturity the cover is ruptured, and the

medusæ have the appearance of a pile of thin saucers attached by the

middle of the convex side. When at length these saucers are set free

as little medusæ, or jellyfishes, the convex side of each saucer,

or swimming-bell, is called the /ex-umbrella/; the concave, under

side, the /subumbrella/. From the center of the subumbrella projects

the /manubrium/, or stomach of the animal. At the free end of the

manubrium is a four-cornered mouth. From the attached end of the

/manubrium/ four tubes or canals diverge, and, extending through the

animal, open into a circular canal which runs around the margin of

the umbrella. When the medusa is as above described, it has reached

the highest point in its development.

When the medusa has matured, it lays eggs, known as /planulæ/. These

are spherical bodies covered with cilia (hairs), by means of which

they swim about for a time; but they finally attach themselves

to some object, there to grow and develop into hydroid colonies.

The cycle of life is thus completed. This process is known as

/alternation of generation/, or /metagenesis/, one life-history

containing two quite different forms of being. The term of life of an

individual is one year, the zoöphyte stage beginning in the autumn

and the medusa stage in the spring.

Some medusæ, besides reproducing by means of eggs, multiply by

budding, small medusæ growing on the manubrium or on the margin of

the umbrella. /Sarsia/ and /Lizzia/ sometimes increase by budding.

The /Hydrozoa/ are not all of the above type. In the sertularians the

zoöids perish on the stem and have no medusa life, their reproductive

element giving rise to the hydroid form without metamorphosis. The

/Trachylinæ/ have no hydroid life, being always free-swimming medusæ;

others, the /Siphonophora/, live a hydroid life which is unattached,

the colony floating on the ocean; the millepores secrete calcareous

skeletons and always remain fixed, reproducing by budding. [pg121]

Hydroids are very abundant, but are comprised in the few groups

mentioned: namely, those which live only in the fixed colonial state;

those which have alternation of generation, being first hydroids

and then swimming-bells, or medusæ; those which live always in the

medusa state, the eggs of the jellyfish developing at once into

other medusæ; and the /Siphonophora/, or those which have a floating

colonial state, the hydroid never being attached, but floating at

large and capable of locomotion, some of the colony having the

function of propulsion.

Hydroids are particularly interesting as exemplifying the close

resemblance that may exist in outward appearance between animal and

vegetable life and as illustrations of communal life and of the

alternation of generation. A few examples of different types are

given below.

ORDER =LEPTOLINIÆ=

The members of this order agree in all essential particulars being

branched colonies having two principal forms of zoöids, the nutritive

and the reproductive. Some genera attain the length of several

inches, or even feet; others are very small tufts growing on shells

and seaweeds. The cup may completely inclose the zoöid and be close

to the stem (sessile), as in sertularians; it may be on the end of

a short stalk, as in campanularians; or it may not reach above the

base of the zoöid, as in tubularians. The genera are based upon these

differences in the perisarc.

The hydroids, like all other classes, exist in such great variety

that it would be impracticable to describe here the many named

species; but to recognize the genera is simple. A long tubular

pedicel without a cup is characteristic of the tubularians; the

campanularians have an arborescent form and bell-shaped cups on

stalks; the sertularians have sessile cups; and the plumularians have

a feather-like form, with zoöid-cups on one side only of the branches.

The beautiful and varied structure of these "animal plants" is most

interesting, and to be fully appreciated they should be seen [pg122]

in life and examined with a glass. Some species are confined to deep

water, but many are littoral and to be found in tide-pools, in the

chinks and crannies of rocks, under stones, and under the hanging

/Fucus/. The horny skeletons of large varieties are frequently washed

ashore, and in their tangled masses smaller living species often may

be found.

THE TUBULARIANS

This division is characterized by zoöids borne on long, slender stems

which are sometimes simple and small, sometimes branching and eight

to ten inches long. The zoöid has two rows of tentacles, the central

one being sometimes on a kind of proboscis. The reproductive zoöids

are in bunches, sometimes below the outer row of tentacles, sometimes

between the two rows. The perisarc does not cover the zoöid. In color

they are commonly red or yellow.

GENUS ^Clava^

^C. leptostyla.^ This species is found growing on /Fucus/, on the

under side of stones at low-water mark, and in tide-pools, where

it often covers several feet of the surface of the rock with a

delicate velvet-like carpet. It is red in color and is, apparently,

a soft and tender species, but it thrives on the most exposed

beaches. The colonies are cylindrical tubes about one quarter of an

inch in height, rising from a creeping stem (/hydrorhiza/). Each

tube is surmounted by a zoöid with fifteen to thirty tentacles,

which is constantly changing form by its contractions. Below the

tentacles are reproductive buds arranged in clusters. Common from

Long Island Sound northward. (Plate XLI.)

[Illustration: PLATE XLI. Clava leptostyla. Tubularia indivisa.

Hybocodon prolifer. Coryne mirabilis. Eudendrium ramosum. Tubularia

Couthouyi.]

GENUS ^Hydractinia^

^H. polyclina.^ The soft, pinkish covering often seen on shells

inhabited by hermit-crabs. This association of two different

kinds of animals is known as /commensalism/, and is a partnership

formed for the benefit of one or both the individuals. In this

case the mossy appearance of the hydroid conceals the shell,

while the stinging-cells with which it is invested are weapons of

defense against the enemies of the crab and also help to paralyze

its prey. In return for these favors the colony is moved about,

thereby obtaining perhaps better oxygenation. Originally it was

thought that /Hydractinia/ lived only on the shells occupied by

hermit-crabs, and that the nomadic life was essential to its

existence; but this is not the case, for it is also found growing

on rocks in tide-pools. These colonies arise from a creeping stem,

which forms a horny, root-like [pg123] network over a surface

and develops at intervals projecting points on which the zoöids

live. Each colony consists of feeding members, of reproductive

members, and of a third kind which seems to have a protective

function. These last are more slender than the others, and are

without tentacles, but are armed with lasso- or stinging-cells. The

colonies are of different sexes, the male being lighter in color

than the female colonies. The eggs develop into planulæ, which swim

about for a while and then give rise to other colonies. It is found

from New Jersey northward, and is very abundant in Long Island

Sound.

GENUS ^Coryne^

^C. mirabilis.^ A hydroid about one inch high, growing in patches

and appearing like tufts of moss on rocks between tide-marks.

When highly magnified it shows club-shaped tubes with pedicels,

terminating in zoöids, scattered over the swollen ends. The

medusa-bud is larger than the others and is lower on the tube. It

liberates a swimming-bell, which is called /Sarsia/. (Plate XLI.)

[Illustration: Colony of /Coryne/, natural size.]

^Sarsia^

^S. mirabilis.^ This medusa of /Coryne/ is from one quarter to

three quarters of an inch in diameter when full-grown. Its umbrella

is nearly hemispherical, and from the center hangs a manubrium.

From the margin of the umbrella hang four very long tentacles. The

shape of its body and the length of its tentacles and proboscis are

constantly changing as it moves in the water. These little medusæ

are very plentiful in the spring and summer, and swim rapidly in

all directions near the surface of the water.

[Illustration: /Sarsia/, the free medusa of /Coryne/.]

GENUS ^Tubularia^

^T. Couthouyi.^ This species is found in the same places as

/Parypha crocea/. The stem is three to six inches long, and is

inclosed in a horny sheath, which is more or less ringed or

jointed, or it may be smooth throughout. The head, when the

tentacles are expanded, measures one and a half inches in diameter.

It has a proboscis covered with tentacles, disposed in series,

which grow successively shorter, the last being merely papillæ. The

medusa-buds hang in clusters between the outer tentacles and the

proboscis. The animal grows in bunches of five to ten tubes, which

spring from a creeping, tangled stem. (Plate XLI.)

GENUS ^Parypha^

^P. crocea.^ This is one of the most beautiful of the tubularians.

It has a large, drooping head on a stem three to [pg124] four

inches long. It is bright red in color, and from the center of the

circle of tentacles the reproductive zoöids hang in a cluster, like

a bunch of grapes. It does not liberate swimming-bells. It is found

in bunches on piles of wharves and bridges, in brackish water, on

the eastern coast as far south as Charleston, South Carolina.

^Corymorpha pendula.^ See Plate XLII.

GENUS ^Hybocodon^

^H. prolifer.^ One of the largest tubularians, somewhat resembling

/Parypha crocea/. It is deep orange in color, and the head is

erect on a long stem. The reproductive zoöids are in a cluster in

the center of a double row of tentacles, and resemble a basket of

fruit. It grows singly, or in groups of two or three, in shaded

tide-pools, which are protected from the surf, and in which the

water is very pure. It is found on the Massachusetts coast, but is

not common. This species liberates swimming-bells. (Plate XLI.)

GENUS ^Pennaria^

^P. tiarella.^ The branches are arranged alternately and at right

angles to a central stem or axis; they taper, being shortest at

the top and bottom of the stem. The zoöids are red in color, and

are arranged along the upper side of branches at considerable

intervals. The stems are black and beaded, being constricted at

intervals. The zoöids have two rows of tentacles, the upper ones

on a small proboscis. From the lower part of the proboscis deep,

bell-shaped bodies, which eventually become swimming-bells, are

developed. The species is found on rocks and eel-grass along the

whole eastern coast.

[Illustration: /Pennaria tiarella/; a branch, natural size.]

^P. gibbosa.^ A species similar to /P. tiarella/, found on the

coast of Florida.

[Illustration: PLATE XLII. Corymorpha pendula. Clytia bicophora.]

[Illustration: PLATE XLII, A. Obelia longissima. Clytia poterium.

Sertularia pumila.]

GENUS ^Bougainvillea^

^B. superciliaris.^ This hydroid is found in tide-pools on the

New England coast, growing in clusters, about two inches high,

attached to rocks or to mussel-shells. The stem is very slender,

and branches. It is red in color. The medusæ which it liberates

are found in great numbers in the spring. The tiny swimming-bells

are nearly globular. The tentacles are long, are arranged in

four clusters on the margin, and extend in every direction. The

manubrium is yellow and short, and the mouth is concealed by four

clusters of short tentacles. On these oral tentacles [pg125]

the eggs of the animal are produced. In its habits it is sluggish,

often remaining in one position for several days.

THE CAMPANULARIANS

The hydroids which have an open, bell-shaped cup at the termination

of a short, stalk-like stem, or branchlet, are mostly campanularians.

This division embraces jellyfishes of different families. Many medusæ

cannot be referred with certainty to the hydroids from which they

sprang, and the medusa-buds of many of the hydroids have not been

noted.

GENUS ^Obelia^ (Plate XLII, A)

^O. commissuralis.^ This is a delicate, much-branched hydroid, five

to six inches long, found at low-water mark in tide-pools, attached

to stones and seaweeds, along the rocky shores from Nova Scotia

to South Carolina. Its branches are arranged spirally and spread

nearly at right angles to the main stem, and the main branches

subdivide in a similar manner. Every interval of the stem has a

slight curve, and at the base of every branch there are four or

five rings. The ultimate branches, or pedicels, bear at their ends

bell-shaped cups which have even edges, but are twelve-sided and

slightly incurved. The pedicels are ringed for the whole length.

The reproductive cups on short ringed pedicels are larger than

the others, and occupy the angles of the branches. These cups are

constricted and again expanded at the apex, forming an urn-like top.

GENUS ^Eucope^

^E. diaphana.^ This species is often abundant on the fronds of

/Laminaria/ washed ashore, and also on /Rhodymenia/ and /Fucus/.

It has a creeping base, zigzag in form, but keeping a straight

course, and in its branching often forming a network over the

surface of the flat fronds. At each angle of the creeping stems

rises a pedicel about an inch high, which inclines in the direction

of the stem and terminates in a zoöid-cup similar in form to that

of /Obelia/. The medusa which this hydroid liberates is called

/Thaumatias diaphana/. The swimming-bell is very shallow and thin,

turning inside out at almost every pulsation. The tentacles are

numerous and rigid like stiff hairs. This little medusa is very

active and is abundant. The species is found from Long Island Sound

northward.

GENUS ^Oceania^

^O. languida.^ This medusa is one inch in diameter and one half of

an inch high, and is so delicate and transparent that it is hardly

visible except in its outlines. In its early stages it is nearly

spherical and has no tentacles; later the disk flattens and has

from thirty-two to thirty-six [pg126] tentacles and numerous

eye-spots. When disturbed it flattens its disk and folds together,

leaving its tentacles sprawled in every direction. It is very

languid in its movements, and often remains in one position for

hours. These medusæ are found only in the hottest hours of the day,

but are very plentiful then, shoals of them often stretching for

miles, and so thick as to touch one another. Their habitat is the

New England coast.

GENUS ^Clytia^

^C. poterium.^ This hydroid is found creeping over seaweeds in

tide-pools from Long Island Sound northward. The main stem is

prostrate, or root-like, running over the body to which it is

attached. The stems rise as do the tubularians. The sterile zoöids

are on single stems about one quarter of an inch high. The stems

are faintly ringed for their entire length, and at the top have

a distinct ring, on which rests an open, bell-shaped cup, which

is smooth around the rim. The reproductive zoöids are on very

short pedicels, and the cups are long and cylindrical, with a wavy

outline. (Plate XLII, A.)

^C. bicophora.^ This species is found in the same places as the

preceding, and is of about the same size. The long stems are more

or less ringed and sometimes branched. The edges of the cups are

notched. The medusa-buds are urn-shaped and ringed, and are on very

short pedicels. (Plate XLII.)

THE SERTULARIANS

The sertularians are distinguished by the horny cup, which is

sessile--that is, set directly against the stem instead of being

raised upon a stalk. They are among the most common objects of the

beach, and, like the plumularians, are often mistaken for plants by

the amateur collector and are gathered and pressed as seaweeds. They

are found everywhere along the coast. They zigzag over the fronds of

seaweeds or hang in fringes upon them, as well as upon rocks, stones,

and shells. They well repay close examination with a glass. Every

open cup bears a wreath of tentacles, which makes the branch a spray

of stars. This is not an inappropriate comparison, for besides their

starry shape some species emit a phosphorescent light.

[Illustration: PLATE XLII, B. Sertularia argentea. Sertularia

cupressina.]

[Illustration: PLATE XLIII. Plumularian hydroid. Aglaophemia

struthioides. Aglaophemia struthioides, magnified. Plumularia

falcata.]

GENUS ^Sertularia^

^S. pumila.^ The most abundant of all the hydroids on the northeast

coast is this species, which is found in profusion upon /Fucus/

and other seaweeds, and mingled with them upon the rocks. It

is easily distinguished from the campanularians because its

zoöid-cups are close against the stems (sessile) instead of on

stalks or pedicels. The stem creeps [pg127] over the fronds

of seaweeds, often crossing and recrossing in a tangled mass. At

short intervals the upright, straight branches rise to one inch or

one and a half inches in height, and are more or less branched.

All except the creeping stems are close set on each side, with

cylindrical zoöid-cups which turn outward at the ends. The cups of

the reproductive zoöids are not sessile; they are much larger than

those of the nutritive ones and are urn-shaped. (Plate XLII, A.)

^S. argentea.^ This is a beautiful species, common from New Jersey

northward. It has a profusion of silvery branches on a dark stem.

The colonies are often a foot or more long, and the branches at

the top and bottom of the stem are shorter and fewer than those in

the middle of the colony. The zoöid-cups are nearly cylindrical,

pressed closely to the stem, nearly opposite or subalternate to one

another, and end in pointed tips. The medusa-bud is urn-shaped,

with two horns at the top. (Plate XLII, B.)

^S. cupressina^, the sea-cypress. This species is similar to

/S. argentea/, but the main stem is thicker and longer, and the

branches less crowded and less subdivided. The branches are arched

or drooping, instead of straight, and gradually decrease in length

at some distance from the lower and upper parts of the stem,

giving a spire-like apex, the stem often continuing into a bare,

branchless extremity. The zoöid-cups are tubular, not much narrowed

or divergent above, and two-lipped on the margin. It is found from

New Jersey northward. (Plate XLII, B.)

THE PLUMULARIANS

These hydroids are feather-like in the manner of branching, short

lateral branches being arranged on each side of a long central stem.

In some species the stems are naked below and resemble quills. The

zoöid-cups are only on one side of the short branches. (Plate XLIII.)

GENUS ^Aglaophemia^

^A. struthioides^, the ostrich-plume. This species, which is

found on the Pacific coast, is perhaps the most beautiful of the

hydroids. It varies in size and color, but always suggests a small

ostrich-plume. The zoöid-cups are arranged in a single row on one

side of each short branch, and the main stem has a joint between

each of the branches, which are placed quite close together. The

rims of the cups have sharp-pointed teeth, and from the top emerge

three tubular projections, which are called /nematophores/, and are

supposed to be degenerate zoöids. At intervals a branch is replaced

by a cylindrical body covered with nematophores, and in these the

generative zoöids are developed. (Plate XLIII.)

GENUS ^Plumularia^

^P. falcata^ (Johnston), or ^Hydrallmania falcata^ (Hincks). This

species is found on shells and rocks near low-water mark from Long

[pg128] Island Sound northward. It is from four to twelve inches

high. The main stem is in long spiral turns, and at intervals has

spreading plumose branches. The zoöid-cups are tubular and closely

pressed against one another, and are ranged in rows on one side of

the branchlets; the apertures of the cups are plain and oblique.

(Plate XLIII.)

FAMILY ~GERYONOPSIDÆ~

GENUS ^Tima^

^T. formosa.^ A very delicate and transparent medusa; size one to

two inches in diameter; bell conical; radial tubes four in number;

manubrium long, hanging far below the disk; four frilled appendages

diverging from the corners of the mouth; tentacles thirty-two;

egg-sacs white and following the line of the radial tubes in

undulating folds. This species is not very common; it is found on

the New England coast.

FAMILY ~ÆQUOREIDÆ~

GENUS ^Zygodactyla^

[Illustration: /Zygodactyla groenlandica./]

^Z. groenlandica.^ Medusa seven to eleven inches in diameter; disk

violet-colored and transparent; margin fringed with long, fine,

contractile tentacles of a darker violet color; numerous radiating

tubes; egg-sacs in slightly waved plates; manubrium hanging below

the line of the disk and with a thin frilled membrane depending

from it. Found north of Cape Cod in July.

ORDER =TRACHYLINÆ=

The /Trachymedusæ/ are characterized by their direct development, the

egg of the jellyfish producing a medusa and not a hydroid colony.

GENUS ^Trachynema^

^T. digitale.^ Size one inch to one and a half inches in height;

rose-colored; the bell thin and hard, and conical at the top. The

swimming is effected by contractions of the muscular velum (the

band around the inner margin of the umbrella) instead of wholly by

the bell. The tentacles are long and numerous, and are curled up

when moving. The manubrium is long and has four expansions at the

mouth. Eight egg-cases [pg129] hang in long pendent sacs from the

upper part of the radial canals and reach nearly to the velum. Four

garnet-colored eyes in club-shaped processes are prominent on the

margin. The animal moves by jerks in straight lines.

ORDER =HYDROCORALLINA=

CALCAREOUS HYDROIDS

[Illustration: /Trachynema digitale./]

The genus ^Millepora^ ("thousand pores"), which is the type of this

order, is a colony of animals, like other hydroids, which secrete

calcareous instead of horny coverings. It differs from true corals

in that the members of a colony perform different functions, whereas

in true corals each member of a community is a complete individual.

It differs also in the arrangement of the stony partitions, which in

=Hydrocorallina= are the outside coverings and connecting canals, but

in true corals are vertical partitions inside the animal, between the

inner and outer sacs, as explained on page 114.

GENUS ^Millepora^

^M. alcicornis^, elk-horn coral. This beautiful coral, which is

abundant in Florida and contributes to the building of the reefs,

rises in broad expansions, more or less lobed, and suggests by its

shape the object for which it is named. The whole mass is porous,

being traversed by innumerable canals. Its surface, although

smooth compared with that of other corals, is covered with very

minute pores, which are of two sizes. The larger ones are the

/gastropores/, or stomach-pores, in which the nutritive animal

lives; it has a cylindrical body, with four knob-like tentacles and

a mouth. Placed more or less irregularly around the gastropores are

smaller pores, the /dactylopores/ (finger-pores), from which emerge

slender mouthless processes, or /dactylozoöids/, with tentacles and

stinging-cells. These seem to be the guard-polyps of the community.

The cups occupied by the zoöids are shallow. As one animal dies,

another succeeds it and builds a horizontal partition separating

the new cup from the old one. Thus the stony mass increases in size

by the progress of succeeding generations of zoöids. The living

animal occupies only the outer, open space. (Plate XLIV.) [pg130]

ORDER =SIPHONOPHORA=

FREE-SWIMMING COLONIES

This order of hydroids consists of free-floating communities and

is one of peculiar interest, since it shows in a clear manner the

special function of each individual member of the colony, and

illustrates better than the foregoing, perhaps, the curious forms of

animal life which this class presents.

GENUS ^Nanomia^

[Illustration: Adult /Nanomia cara/.]

^N. cara.^ This species is found on the New England coast. The

members of the community are arranged along a hollow stem about

three inches long which opens into every individual. At the top

of the stem is a sac, or float; just below this is a group of

swimming-bells which have no manubrium or mouth, and whose sole

function is to provide locomotion for the community; and below

these are three sets of zoöids, each having a triangular shield

and tentacles. The tentacles are longer than the main stem. One of

these last groups consists of the nutritive members, the mouths

of the community, resembling manubriums of swimming-bells out of

place. Each one has at the point of attachment a bunch of long,

delicate tentacles having pendent knobs of lasso-cells. A second

group, also with mouths, has shorter tentacles which are carried in

spiral coils. The members of the third group have but one tentacle

each and resemble the float at the end of the stem; presumably

these drop off and produce new colonies. There are also on the

lower part of the stem other reproductive members, which resemble

the clusters of buds seen on [pg131] tubularian hydroids. These

animals are pink in color and move through the water with a

graceful swaying motion.

GENUS ^Physalia^

[Illustration: /Physalia arethusa/; Portuguese man-of-war, one fifth

natural size.]

^P. arethusa^, the Portuguese man-of-war. This colony is perhaps

the best-known one of the group, since it attracts much attention

in Southern waters, and is also one of the most remarkable

examples of an animal community. The most prominent part of the

compound body is the float, an oblong pear-shaped bag, full of

air, which floats on the surface of the water. Its color is bright

blue, varying to rose. On the upper side of this air-vessel is a

crest, or sail, and from the under side depend long tentacles, or

streamers. Some of these tentacles are covered with stinging- or

lasso-cells; some are the feeding zoöids, with flask-shaped

bodies, and some, which look like bunches of grapes, are the

reproductive zoöids. The tentacles in this curious cluster are

all close together and hang from one side of the float, near the

broader end. The longest are on the outside, which may be called

the windward side, since they serve to keep the crest, or sail,

before the wind; and when the wind is strong they stretch out to

a remarkable length,--forty to fifty feet,--acting as anchors to

keep the colony from being driven ashore. They also change its

course by raising the pointed end of the float, thus forcing it to

"come about." These long tentacles, ordinarily carried more or less

curled up, are in bunches of two to four, and emerge from a common

stem. Clusters of similar, but smaller, tentacles alternate with

the larger ones, but grow somewhat nearer the pointed end of the

float; these are purely locomotive organs. Next come two smaller

sets of appendages, also of unequal size, which are the nutritive

organs of the community. They are clustered together on a stem like

the others. The appendages of the third kind are small, resemble

bunches of grapes, and are scattered among the nutritive hydræ.

These last are the reproductive zoöids of the community.

GENUS ^Vellela^

^V. limbosa.^ This hydroid is abundant on the Florida coast. It

has a bright-blue, flattened, oblong, bladder-like float, four to

five inches [pg132] long, which, is divided into a number of

concentric, communicating compartments. The margin of the float is

entire, and a triangular sail extends diagonally across the top. On

the under side is a single mouth on a manubrium, and surrounding it

are a large number of short thread-like appendages having different

functions. Some of them are feelers, others bear reproductive buds,

and others have stinging-cells. Associated with /Vellela/ is an

allied hydroid called /Porpita/, which has no sail, and in company

with these two is a jellyfish called /Rataria/, which is supposed

to be the offspring of one or the other of them.

[Illustration: /Vellela limbosa./]

TABLE SHOWING THE CLASSIFICATION OF THE SCYPHOZOA DESCRIBED IN THIS

CHAPTER

Class =SCYPHOZOA= (/Velum usually absent and tentaculocysts

present; the eggs are discharged into a gastric cavity. The type

of this class is Aurelia/)

Order =STAUROMEDUSÆ= (/Umbrella conical or vase-shaped; no

tentaculocysts/)

Genera Species

^Lucernaria^ ^L. auricula^

Order =PEROMEDUSÆ= (/Umbrella conical and divided by transverse

constrictions; four interradial tentaculocysts/)

^Pericolpa^ ^P. quadrigata^

Order =CUBOMEDUSÆ= (/Umbrella four-sided, cup-shaped; four

perradial tentaculocysts/)

^Charybdæa^ ^C. marsupialis^

Order =DISCOMEDUSÆ= (/Flattened, saucer-like or disk-shaped

umbrella; radial tubes branched; eight tentaculocysts/)

Suborder ~CONNOSTOMÆ~ (/Very small; marginal tentacles; short

and solid; mouth square without arms/)

Suborder ~SEMOSTOMÆ~ (/Square mouth with four long arms;

tentacles long and hollow/)

^Aurelia^ ^A. flavidula^

^Cyanea^ ^C. arctica^

^C. fulva^

^C. versicolor^

^Linerges^ ^L. mercurius^

^Pelagia^ ^P. cyanella^

Suborder ~RHIZOSTOMÆ~ ("/Root-mouth/") (/Mouth obliterated by

growth of oral arms across it; tentacles absent/)

^Cassiopeia^ ^C. frondosa^

[pg134]

CLASS =SCYPHOZOA=

THE LARGE JELLYFISHES

There is perhaps no marine animal which excites more wonder than

the jellyfish. Its transparency, its graceful rhythmical movements,

its long streaming tentacles, the variety and eccentricity of its

form, and often of its color, attract attention, and one naturally

desires to know something of its life-history. Jellyfishes are also

called /medusæ/, because their long appendages suggest the locks of

the Gorgon; /acalephs/, on account of their stinging or nettle-like

properties; and sun-jellies, sea-blubbers, etc., because they float

upon the surface during the warmest part of the day, when the sun is

high. The name /jellyfish/ is inappropriate, since the animal in no

way resembles a fish except in the fact that it swims; but it is,

nevertheless, the commonest name.

Jellyfishes vary in size from that of a pinhead to six or seven

feet in diameter. They differ in the number, size, and position of

the tentacles, the number of the radial canals, the form of the

manubrium, the position of the egg-sacs, etc.; but the general plan

of the internal structure is the same in all species. In shape they

are compared to a mushroom. From the center of an umbrella-like top

falls a central organ like the stalk of a mushroom. It is called the

/manubrium/ and is the mouth and stomach of the animal.

From the top of the manubrium radiate straight or branched tubes,

which are connected with a canal which runs around the whole margin

of the umbrella. Extending around the inner circumference of the

disk in certain species (usually the hydroid medusæ), there is a

horizontal shelf, called the /velum/, or veil, because it sometimes

falls like a veil. [pg135]

From the margin of the umbrella depend the tentacles. There are

little mineral deposits, like crystals, called /lithocysts/, disposed

at intervals on the margin, and known also as /marginal bodies/,

which are supposed to be eyes. In some species these lithocysts

are inclosed in club-shaped bodies, and they are then called

/tentaculocysts/, because they are like small tentacles. These,

together with the nerve-fibers, are called the sense-organs; but to

what extent jellyfishes can see and feel is undetermined. This is

the first appearance of sense-organs in animals. Around the concave

surface of the umbrella is a muscular zone, or zone of contractile

tissue, by which the animal opens and shuts the umbrella and gets its

locomotive power. The /gonads/, which are conspicuous from being more

opaque than the rest of the body, are the egg- or sperm-sacs. They

vary in form and in position.

The jellyfish is carnivorous, feeding on small organisms such

as crustaceans and even fishes. The tentacles are invested with

stinging-cells, as are also the frills about the mouth, when such

occur. With these stinging-cells, which are in some species so

powerful as to have been compared with an electric battery, the

jellyfish benumbs its prey. The stinging properties are due to

nettle-like threads contained in poison-cells. When these penetrate

the flesh they produce a pain similar to that of an electric shock.

The food is taken into the manubrium by the square mouth at its

free end, and is there digested. It is then sent as nutritive fluid

through the canal system of the body, and ejected through small pores

in the canal which surrounds the margin of the umbrella.

There are two sexes. The gonads of the female contain eggs; those of

the male, sperms. The contents of the gonads drop into the central

cavity and pass out through the mouth. The fertilized ovum is called

a /planula/, and is a transparent sphere covered with cilia, by

means of which it swims about for a time. At length it attaches

itself to some object, and becomes in some species a branching colony

(hydroid), in other species a /strobila/. The latter, as it grows,

is constricted at intervals, and at maturity resembles a pile of

inverted saucers with lobed edges. Each of [pg136] these saucers

is finally detached, and when liberated is called an /ephyrula/,

and becomes a jellyfish. Thus its cycle of life is complete. There

are some species which, having no hydroid or strobila state, mature

without alternation of generation (/metagenesis/).

The term of life of the jellyfish does not exceed one year. Even the

giant /Cyanea/ attains its immense growth in six months. It starts

in the spring as an ephyrula, not more than one half of an inch in

diameter, and when it dies in the autumn is often six to eight feet

in diameter. The bodies of jellyfishes are ninety-nine per cent.

water, and the dead ones thrown upon the beaches by the autumn storms

rapidly disappear, leaving no traces behind.

The powerful stinging-cells with which the large medusæ are armed

make them formidable enemies, and it is probable that some deaths

by drowning are caused by swimmers encountering them and becoming

paralyzed by them.

ORDER =STAUROMEDUSÆ=

("/Cross-medusæ/")

GENUS ^Lucernaria^

^L. auricula.^ This little iridescent jellyfish, which measures

about one and a half inches in diameter, is commonly found attached

to eel-grass by a stalk-like projection of the top of the umbrella.

Short, globe-tipped tentacles are arranged in eight clusters, each

cluster on a raised prolongation of the margin of the umbrella, and

in the center of each space between them is a dark kidney-shaped

organ called the /anchor/. These anchors are used for holding,

either for suspension or when moving from place to place. The

mouth forms a slight quadrangular projection in the center of the

bell-like expansion. The arm-like projections are mottled with

two rows of spots, which are the ova. Although a free form and

capable of moving about, /Lucernaria/ is sedentary in habit. It is

sometimes found free, but generally attached by its extremity to

eel-grass or /Fucus/, seldom to rocks. It is constantly changing

its shape. The one it most frequently assumes is that of a cup or

inverted bell. It is found on the New England coast. (Plate XLIV.)

ORDER =PEROMEDUSÆ=

("/Maimed medusæ/")

GENUS ^Pericolpa^

^P. quadrigata.^ Umbrella conical and divided by a horizontal

constriction into two parts, the lower one being again divided into

lobes. There are four long tentacles and four tentaculocysts. It is

not found on the coasts of the United States. [pg137]

ORDER =CUBOMEDUSÆ=

("/Cube-medusæ/")

GENUS ^Charybdæa^

^C. marsupialis.^ Umbrella square, flattened on top, and of firm

consistency. Four tentacles fall from lobes on the umbrella, and

four club-shaped eyes are in marginal notches. Plate-like egg-sacs

follow each side of the four radial canals. The bell is one inch

in diameter and about two inches in height. It is not found on the

coasts of the United States.

ORDER =DISCOMEDUSÆ=

("/Disk-medusæ/")

SUBORDER ~SEMOSTOMÆ~

GENUS ^Aurelia^

[Illustration: /Aurelia flavidula/, about one fourth natural size.]

^A. flavidula.^ Size eight to ten inches in diameter; disk

gelatinous, transparent bluish-white, broad and comparatively flat,

with a fringe of short tentacles of even length around the margin;

margin broken by eight notches, in each one of which is a club-like

organ (/tentaculocyst/) containing calcareous spots or eyes, which

are hidden by lappets or hood-like coverings; groups of nerve-cells

also lie in the marginal notches; radial canals branched; manubrium

very short, with square mouth, which is surrounded by delicate

membranes, or oral arms, each arm being a folded membrane tapering

to a point. The edges of the membranes are covered with lasso- or

stinging-cells. Four egg-sacs, or gonads, are conspicuous in

horseshoe shape around the center of the disk. The gonads are

pink in the males, and yellow in the females. These medusæ swim

in shoals, and are common everywhere in summer. They may be said

to be annual animals, for they make their appearance regularly as

free-swimming medusæ in the latter part of April, when they may be

seen in immense numbers near the surface when the water is smooth

and the sky clear. At this time they are about an inch in diameter.

They grow rapidly, and by the end of June have attained their full

size. At [pg138] the end of July they are fully developed, and

begin to discharge their eggs, which go into the folds around the

mouth and remain there until they attain the planula stage. After

the spawning period the medusæ, reduced in strength, are unable

to resist the storms of the autumn, and many of them are cast

ashore; many others, in a more or less wasted condition, float

near the surface, but the body is less transparent, its tissues

are thickened, its tentacles gone, and general dissolution has

commenced. In this condition the medusæ are frequently capsized by

the air which accumulates in the empty egg-cavities, and, floating

helplessly on the surface, are attacked and destroyed by swarms of

small crustaceans; thus their cycle of life is terminated. It has

been suggested that the destruction of the mothers, by being cast

upon the beaches in the autumnal gales, is a provision to set free

the planulæ in a position favorable to their existence; for when

liberated they fasten upon the rocks and seaweeds of the shore,

where, during the winter months, they develop into strobilæ, which

in turn free their saucer-like disks early in April.

[Illustration: Strobila of /Aurelia flavidula/.]

GENUS ^Cyanea^

[Illustration: /Cyanea arctica/, greatly reduced in size.]

^C. arctica^, the sun-jelly or sea-blubber. This is the largest

jellyfish known. Some individuals measure seven and a half feet

across the disk and have tentacles more than one hundred feet long.

Usually they are three to five feet in diameter, with tentacles

thirty to forty feet long. The disk is red, the margin white and

scalloped. The tentacles, of different colors, are covered with

lasso- or stinging-cells, and are arranged in eight distinct,

thick clusters on the margin. From the mouth hang four long and

very broad, thin curtains, much folded and ruffled, whose edges at

times look as if they were embroidered, because great numbers of

discharged eggs are attached to them. Four egg-sacs hang from the

disk near the manubrium, and eight sense-organs (tentaculocysts),

in hardened coverings, lie in some of the deep incisions of the

margin. /Cyanea/ [pg139] is usually solitary, seldom being seen

in company with others. It is common on the New England coast,

and is frequently found stranded on the beach, where it in no way

suggests the beautiful appearance it presents when floating in

the water. Like /Aurelia/, /Cyanea/ has a strobila stage. It is

supposed that the young remain near the bottom, for they are seldom

seen, while adults are plentiful. They begin to appear in numbers

at the end of summer from Cape Cod northward.

^C. fulva.^ This species is found in midsummer south of Cape Cod

and is common in Long Island Sound. Its general color is light

yellowish-brown, the flowing curtains being the darkest part of

the animal. It is not as large as C. arctica, and the lobes of the

margin are deeper and more rounded.

^C. versicolor.^ The whole disk is bluish milky-white, the flowing

curtains are light brown, and the tentacles are pink. It is not so

large as /C. arctica/. Found in the spring on the southern coast.

[Illustration: /Linerges mercurius/, thimble-fish.]

GENUS ^Linerges^

^L. mercurius^, the thimble-fish. The English name indicates the

form as well as the size of this little brownish jellyfish, which

is found near the Florida Keys, extending in lines for considerable

distances.

GENUS ^Pelagia^

^P. cyanella.^ Umbrella spherical, margin scalloped, tentacles

eight in number; four long appendages ruffled on the edges hang

from the mouth; size about two inches in diameter; appendages four

inches long; color pink. (See next page.)

SUBORDER ~RHIZOSTOMÆ~

The =Rhizostomæ=, or root-mouth jellyfishes, are very remarkable.

They have no tentacles, but covering the end of the manubrium and

hanging from it like tentacles are oval appendages with numerous

minute funnel-like apertures, called suctorial mouths. As the manner

of locomotion of jellyfishes is peculiar to themselves, so also is

this many-mouthed development unique in the animal kingdom. The

type of this group, described below, is found on the Florida Keys.

The different species vary in diameter from three to eight inches.

[pg140]

GENUS ^Cassiopeia^

[Illustration: /Pelagia cyanella./]

^C. frondosa.^ This species has a circular disk, on the margin of

which are sixteen sense-organs (tentaculocysts), but no tentacles.

The lower end of the manubrium, which in other jellyfishes is

an open mouth, is closed by eight arms which emanate from it

and are usually extended laterally, lying parallel to the disk.

These arms are much branched, and the branches, in turn, have

numerous appendages. Some of these appendages look like little

polyps and have mouths surrounded by crowns of tentacles; others

are ovoid bodies without external openings, but with a central

cavity connected with vessels leading to the arms. The former are

mouths, but the function of the ovoid bodies is not known. Although

able to swim freely, /Cassiopeia/ lies usually on its back, as if

attached, and languidly opens and closes its disk, rarely changing

its position. Its arms, extending upward, appear like the fronds of

algæ. These jellyfishes are common on the Florida coast, huddled

together on the sands of the coral reefs. (Plate XLIV.) [pg141]

TABLE SHOWING THE CLASSIFICATION OF THE ACTINOZOA DESCRIBED IN THIS

CHAPTER

Class =ACTINOZOA=

Subclass =Zoantharia= (/Mesenteries numerous, usually in

multiples of six; tentacles unbranched hollow cones/)

Order =ACTINIARIA= (/The sea-anemones. Single; no skeleton/)

Genera Species

^Metridium^ ^M. marginatum^

^Rhodactinia^ ^R. davidsii^

^Holocampa^ ^H. producta^

^Sagartia^ ^S. leucolena^

Order =MADREPORARIA= (/The stone- or reef-corals. Colonies;

skeleton calcareous/)

^Oculina^

^Astræa^

^Meandrina^

^Diploria^ ^D. cerebriformis^

^Madrepora^ ^M. cervicornis^

^M. palmata^

^Astrangia^ ^A. danaë^

Order =ANTIPATHARIA= (/The black corals/)

Subclass =Alcyonaria or Halcyonoida= (/Tentacles and mesenteries

eight in number; tentacles feathered, that is, with uniform

branches/)

Order =ALCYONACEA=

^Alcyonium^ ^A. palmatum^

^Tubipora^

Order =GORGONACEA= (/The sea-fans and sea-whips. Compound,

tree-like colonies, with horny axis, branching throughout/)

Order =PENNATULACEA= (/Free, phosphorescent; colonies, with

horny axis; polyps in lateral branches/)

^Pennatula^

[pg142]

CLASS =ACTINOZOA=

SEA-ANEMONES, REEF-CORALS, SEA-FANS, SEA-WHIPS, AND SEA-PENS

The animals of this class are divided into two subclasses, based on

the following anatomical differences: In the first subdivision, which

includes the sea-anemones and the reef-building corals, the polyps

have numerous simple, hollow tentacles and radial partitions of the

same number, both being some multiple of six. The polyps of a colony

are all alike, and the hard matter they secrete is carbonate of lime.

In the second subdivision, the /Alcyonaria/,--or halcyonoids, as they

are commonly called,--the tentacles and radial partitions are always

eight in number, and the tentacles have small symmetrical appendages

or branches. The polyps of this group are often accompanied by

small zoöids having no tentacles. The hard secretions are horny

and elastic, as in sea-fans, sea-whips, and sea-pens, or they are

extremely hard, as in /Corallina rubrum/.

SUBCLASS =ZOANTHARIA=

("/Animal-flowers/")

ORDER =ACTINIARIA=

SEA-ANEMONES

These curious and, at times, beautiful creatures are polyps, and are

constructed on the radial system. They have a cylindrical body with

a broad base and rows of hollow tentacles around the upper disk.

They have a central sac, and a space between the outer and inner

sacs which is divided vertically by walls called /mesenteries/, as

explained on page 114. Each tentacle, however many there [pg143] may

be, has a corresponding chamber. The inner sac has a mouth, like a

slit, at the top of the disk, opening to the outside, and it also has

openings into the chambered spaces which surround it. These chambers

also open into the hollow tentacles; thus a continuous circulation

throughout the whole animal is established.

The food taken in at the mouth is digested in the inner sac, passes

through all the chambers of the cavity as nutritive fluid, and is

then expelled at the mouth again. The inner sac, or gullet, has

longitudinal grooves; two of these are broad and deep, and correspond

to the corners of the mouth. These are called /siphonoglyphs/. The

sea-anemone is soft and contractile, and belongs to the only order

of this class which does not secrete a skeleton. It has two sets of

muscles, one of which extends from the base to the summit of the body

and is placed on the dividing partitions. Sea-anemones are classified

by the arrangement of the septa and the manner in which the muscles

are placed upon them. The other set of muscles is arranged around

the circumference of the column or body. Each tentacle is furnished

with similar sets of muscles. The animal is sensitive, and at the

least alarm contracts its body by means of these muscles, and

quickly transforms itself from a beautiful, flower-like form into a

shapeless, unattractive, inconspicuous mass.

The /Actiniaria/ are developed from the egg. The eggs form on the

edges of the inner walls (mesenteries), and when mature drop into

the outer sac (gullet), and out of the mouth as ciliated spheres

(planulæ). After swimming about for a time these attach themselves to

rocks, and, conforming to the irregularities of the surface, secure a

tight hold. The upper surface of the planula then becomes depressed

and forms a gullet, and in time a complete animal is formed. The

/Actiniaria/ reproduce also by budding. A small protuberance or

simple elevation of the body-wall appears on the side at the base,

or in some species on the disk of the animal, which generally

develops into a complete animal and at maturity falls away from the

parent. Sometimes several anemones bud simultaneously from the same

individual, and a third generation commences to bud at the same

time from the immature young of the parent stock. The sea-anemones

increase [pg144] also by self-division. In this case a constriction

is formed, which gradually deepens and forms a complete partition of

the body, and two individuals exist where originally there was but

one.

The /Actiniaria/ are carnivorous and very voracious. They feed

on small organisms and on shell-fish and crustaceans, which they

suck out of their shells. To secure their prey they are armed with

an abundant supply of stinging-cells on the tentacles, and also

with fine stinging-threads which are ejected from pores which are

distributed over the whole body.

Sea-anemones vary greatly in color and form, and when expanded

suggest flowers, but do not resemble the one for which they are

named. They abound on every shore, the same genus often being found

in widely separated regions. They are larger and more highly colored

in tropical waters. Many of the species are littoral, and are found

in the tide-pools of rocky caverns, on the under side of rocks, and

on the piles of wharves and bridges at low-water mark. The majority

of them are attached, but are able to change their location; others,

/Edwardsia/ and /Cerianthus/, swim about when young, and in the

adult state burrow in the sand or mud, leaving only their tentacles

exposed. /Bucidium parasiticum/ is parasitic on the folds of the

membrane which hangs from the mouth of the large jellyfish /Cyanea

arctica/. /Fenja/ and /Peachia/ lie on the sea-bottom, with their

bodies horizontal like a worm, the mouth-end and tentacles erect.

/Adamsia palliata/ furnishes another example of commensalism; it

lives on the back of shells, commonly the whelk, inhabited by

hermit-crabs. /Minyas/ is pelagic; it has a float at one end, and by

means of its tentacles swims about freely.

A very few species only are described below, since these polyps are

unmistakable, being always columnar bodies, with the upper disk more

or less crowded with tentacles, and so brilliant in coloring and

beautiful in form as to attract attention if found in the expanded

state; otherwise they are easily overlooked.

GENUS ^Metridium^

^M. marginatum.^ This is the most conspicuous and abundant

sea-anemone of the northeastern coast. It is common from New York

[pg145] northward, and is found near low-water mark in tide-pools,

on the under side of large stones, in sheltered crevices of rocks,

and on the piles of wharves and bridges. In contraction it is a

broad, low cone, but when expanded is sometimes ten inches across

the disk. Allied species found in Florida are eighteen inches in

diameter. The column is smooth, cylindrical, and broader than

long. At the top is a slightly elevated, thickened fold, and

above this a deeply folded and frilled margin, with numerous

fine, short tentacles, appearing like a fringe, which cover the

upper side of the disk half-way to the oval mouth. The color is

exceedingly variable; commonly the column is yellowish-brown, but

it may be pink, white, salmon, orange, or dark brown, or striped

or mottled with different colors. The disk and folds are lighter

or flesh-colored, and the tentacles are of varying colors, usually

grayish with tips of brighter colors. When irritated this species

throws out from the column numbers of long, slender white threads

(/acontia/), which are covered with minute stinging-cells. These

organs of defense protect the animal from the attacks of many

enemies.

GENUS ^Rhodactinia^

^R. davidsii^ (Agassiz), ^Tealia crassiformis^ (Gosse), the

thick-petaled rose-anemone. The color varies, being often

bluish-green mottled with crimson, often bright cherry-red, with

the thick tentacles somewhat lighter in shade, or flesh-colored.

The animal is found in shallow water. It assumes various shapes,

changing every few minutes. The tentacles are short, conical, and

uniform in size; the column, the breadth of which is greater than

its height, often has wart-like processes in longitudinal lines.

The diameter of the disk is about three inches. Found from Cape Cod

northward in tide-pools and on ledges covered with /Fucus/.

GENUS ^Holocampa^

^H. producta.^ Its column, stretched to its full extent, is a foot

in length and about an inch in diameter, but when contracted is

much shorter and thicker. It has but twenty tentacles, and these

have swollen tips. Rows of suckers extend the length of the column.

It ranges from Cape Cod to South Carolina, and is found under rocks

at low-tide mark, and also on sandy beaches, buried in the sand,

with its tentacles only above the surface.

GENUS ^Sagartia^

^S. leucolena^, the white-armed anemone. It ranges from Cape Cod

to North Carolina, and is common in Long Island Sound, being found

at low-water mark on the under side of stones. The column is

elongated, cylindrical, translucent, flesh-colored, with simple

plain disk and long, slender, whitish tentacles crowded together

near the margin. [pg146]

ORDER =MADREPORARIA=

STONE- OR REEF-CORALS

The coral resembles the sea-anemone and is a polyp constructed on the

radial plan (page 113). It lives in colonies, but, unlike the hydroid

colonies, each polyp of the community is a complete organism, and

in the reef-building corals all the individual polyps of a colony

are alike. The home of each animal is called a /corallite/, and the

aggregation of many corallites is a /corallum/.

The corallite is composed of carbonate of lime secreted by the polyp,

and, broadly speaking, may be called a skeleton. The secretion forms

a basal plate and radiating partitions between the mesenteries in

the cavity of the animal, and also surrounds the polyp like a cup.

In some species this is a solid substance; in others it is like a

network through which the animal substance (c[oe]nosarc) of the

zoöids of the colony is connected, as in /Madrepora/.

The polyps reproduce by budding and by self-division (fission),

in a manner similar to that of sea-anemones. The way in which the

budding or the fission takes place determines the shape of the

colony, or corallum, which has a great variety of forms. In some

species the budding is confined to certain individuals of the colony.

In this case the branched forms result. When growth takes place by

fission, hemispherical masses are formed, which are often perfectly

symmetrical, as in the so-called brain-corals. In /Astræa/ the polyps

are inclosed separately, but in /Meandrina/ fission is confined to

the upper half of the polyps, so that a complex polyp is formed, with

several mouths opening into a common stomach, making long serpentine

furrows on the corallum.

Some of the genera of the second subdivision, the alcyonarians,

differ materially from the ordinary idea of corals, as their

framework is of a horny and more or less flexible material (chitin).

Of these are the sea-fans, sea-whips, and sea-pens. The organ-pipe

coral of the same subdivision is an example of an exceedingly

fragile lime structure, while the red coral, /Corallina rubrum/,

[pg147] the species so much used for ornamental purposes, has an

exceedingly hard and stony character. The madrepore corals are called

reef-builders, but not in the sense of constructors of reefs. They do

not erect definite structures as bees do. It is the aggregation of

the skeletons of the dead polyps, together with other agencies, which

forms a reef. The coral polyps, though so minute individually, are

almost infinite in numbers. It is estimated that the colonies rise

one half of an inch in ten years.

Corals live at different depths in the sea. Those which form the base

of the reef are the astræans, which do not live above a depth of six

fathoms. They are characterized by little star-shaped spots on the

corallum, the radial partitions meeting in the center of the spots,

or corallites. Next above the astræans come the mæandrinas and the

porites. The former have elongated openings which extend in waving

furrows over the surface. The porites resemble astræans, but the pits

are smaller, with fewer partitions, and the substance is more porous.

Above these and capping the reefs are the beautiful branching and

palmate madreporians, together with millepores, numerous varieties of

sea-fans (/Gorgonacea/), and the calcareous seaweeds (nullipores),

making a garden of beautiful branching forms of every shape and color.

The coral reef is as thickly inhabited by other living organisms

as is the forest by birds and insects. Mollusks, worms, crabs,

starfishes, and sea-urchins find resting-places there and work

destruction to the coral masses, as they bore and penetrate the reef

in various ways until large fragments of it are detached and either

washed by the waves to places far from their foundation, or ground

to sand, which, filling the interstices of the reef, adds to its

solidity.

The living coral is quite different in appearance from the bleached

skeletons commonly seen. The surface of the corallum is often soft

and downy, from the numerous waving tentacles, and its coloring is

vivid and varied. The madrepores are pink, yellow, green, brown, and

purple. /Tubipora/, the organ-pipe coral, has green polyps emanating

from its red tubes. White polyps in star-like form dot the branches

of the red coral of commerce, /Corallina rubrum/. The whole mass

of /Helipora/ is bright blue, [pg148] and the beautiful sea-pens

are both highly colored and phosphorescent. Owing to the fact that

these brilliantly colored polyps were mistaken for blossoms, the

recognition of their true character was long delayed, they having

been ranked as vegetables until comparatively recent times.

With few exceptions, corals do not grow in water below the

temperature of 68°, hence they are inhabitants of tropical and

subtropical waters. The Florida Keys are coral reefs, and the species

described below are to be found there.

GENUS ^Oculina^

Arborescent; corallites arranged somewhat spirally on branches and

widely separated; branches compact between corallites. Each bud is

for a time at the apex of the branch, but finally becomes lateral,

and then gives off another bud from its upper surface, and so the

stem lengthens. (Plate XLIV.)

GENUS ^Astræa^

The star-corals. The corals of this genus are hemispherical masses

covered with small star-shaped pits, or corallites. Although the

diameter of an astræa-dome may be twelve feet or more, it has only

one half or three quarters of an inch of living coral on its surface,

the rest being solid matter left behind as the polyps rose in growth.

The colony increases by self-division. The septa meet in the center

of the corallite, making star-like pits; the surface is comparatively

smooth. (Plate XLIV.)

Genera ^Meandrina^, ^Diploria^

Corallum massive, hemispherical in shape, with furrows running in

irregular lines over the whole surface. The peculiar serpentine form

of the corallite is produced by the animal growing in one direction,

fission being incomplete, and new mouths being successively opened

until a line of them extends along a common stomach.

^D. cerebriformis.^ This species is commonly known as brain-coral

or brain-stone. The hemispherical shape, together with the peculiar

serpentine corallites, makes its resemblance to the human brain

very noticeable and the name unusually appropriate. This species,

when living, is bright yellow. (Plate XLV.)

[Illustration: PLATE XLIV. Millepora alcicornis. Lucernaria auricula.

Cassiopeia frondosa. Astræa argus. Oculina.]

[Illustration: PLATE XLV. Porites furcata and P. astræaoides. Diplora

cerebriformis. Madrepora cervicornis. Madrepora palmata. Mycedium

fragile.]

GENUS ^Madrepora^

Some species of these corals appear like branches, while others

have flat, low surfaces or fronds; all of them are covered with

innumerable small cylindrical cups. Each cup is the home of a polyp,

which secretes calcareous matter around its column, and septa between

its radial partitions. The corallum, when examined with a glass,

looks like meshwork. Through the fine openings of the porous surface,

the polyps of the colony are connected by interlacing tubes of animal

substance (c[oe]nosarc). The polyps of the madrepore colonies are

small in comparison with the connecting structure, which becomes very

massive; but, although large, the corallum is fragile, on account of

its perforated character and the exceeding delicacy of its parts.

In species which form incrustations, new polyps arise from tissue

which spreads beyond the corallites. In some species certain polyps

and corallites increase in length, growing longitudinally, and

continually form buds around the base. This manner of growth leads

to the formation of branches, while the former manner gives lateral

extension. Both of these forms of budding may take place at the same

time in the same colony. The madrepores are among the most common of

the reef-builders. They form reefs which extend for miles around the

Florida Keys.

^M. cervicornis^, the stag-horn coral. This is a branching species

which attains large size. Its manner of growth is as follows: At

the tip of each branch is an individual polyp, which is larger

than those which surround the branch. This is the original animal

which started the branch, and is the parent from which all the

others on the branch have budded. The large terminal polyp buds

around the base; a surplus of lime also collects at the base and

clogs its tissues, so that it no longer can perform the functions

of life, and after a certain period the base becomes dead matter.

The polyp on the upper end continues to live and rises above the

excess of solid matter. At the same time it continues to form new

buds. The buds become independent corallites and secrete an excess

of calcareous matter at their bases, which cements them to the

parent stock and increases the thickness of the branch. Thus, as

the original polyp constantly rises and buds, the colony assumes a

stem-like form, covered with numerous individuals. Certain polyps

on the main stem have the attributes of the parent animal. These

start branches, and so the process goes on, and in time the colony

becomes much branched and arborescent in form. In the living coral

each little polyp is like a minute sea-anemone, having a colored

cylindrical body surrounded on its upper disk with numerous

tentacles. (Plate XLV.) [pg150]

^M. palmata.^ This madrepore grows like the one described above,

except that the branches do not remain separated, but unite or grow

together, giving broad, flat surfaces which resemble fronds. When

carefully examined these surfaces show striations which indicate

the course of the branches. The structures forming the lobes are

caused by the failure of the branches to unite. On the Carysfort

Reef of the Florida Keys this species covers the top of the reef

for several miles, nearly reaching the surface, and appears like a

vast bed of low yellow shrubbery. (Plate XLV.)

GENUS ^Astrangia^

^A. danaë.^ A small coral found on the New England coast. It lives

in the clefts of rocks in small patches, sometimes two to three

inches across and one quarter of an inch or more high. Frequently

it is like a thin crust of lime covered with star-like divisions.

Sometimes it forms branches. The living animals are white, and

when expanded rise above the cells and resemble a cluster of small

sea-anemones.

SUBCLASS =ALCYONARIA= or =HALCYONOIDA=

[Illustration: /Alcyonium palmatum/: /A/, entire colony; /B/,

spicules.]

In this subclass--the actinoid corals--the polyps are of two kinds.

The smaller are without tentacles and are called /siphonozoöids/. The

larger have but eight radial partitions and eight tentacles. This

limitation of parts places them in a higher rank than the corals of

the first subclass. Another characteristic of these polyps is the

presence of symmetrical branchlets on the tentacles, which give them

a feather-like appearance. These corals are called halcyonoids.

[pg151]

Some of them may easily be fancied to have been selected for

halcyons' nests, as the name suggests--the sea-fans, for example.

ORDER =ALCYONACEA=

GENUS ^Alcyonium^

^A. palmatum.^ This coral community is found sometimes at low-water

mark, but usually in deeper water, attached to shells and stones.

It is commonly known as dead-men's-fingers, an unpleasant name

given it by fishermen because of a fancied resemblance to a human

hand with only the stumps of the fingers. The substance of the

coral is semi-cartilaginous, with scattered spicules of lime which

give it stability. When the polyps are fully extended the colony

is rather attractive in appearance, but not so when contracted.

It is found in abundance on the New England coast. An immense

/Alcyonium/, /Paragorgia arborea/, grows on the fishing-banks off

Newfoundland, and is sometimes brought up on the fishing-lines. It

is tree-like in form, and measures six feet or more in length.

GENUS ^Tubipora^

[Illustration: /Tubipora/, organ-pipe coral, natural size.]

The organ-pipe coral. This genus, which is deep red in color and very

fragile, consists of many tubes slightly separated from [pg152] one

another, but connected by horizontal platforms at short intervals.

The form of reproduction, by budding, in this colony is peculiar to

itself. The spicules of lime secreted in the polyp unite or fuse into

a tube or cylindrical skeleton. At certain stages of development

the polyp sends out a horizontal expansion, which unites with the

expansions of other polyps and becomes calcified, forming a shelf

which binds the tubes together. From the top of the platforms other

corallites are formed, and thus a colony is made, which broadens as

it rises in its growth. The body of the polyp is green, the skeleton

red. It belongs to the East Indian seas and is given here only as an

example of a peculiar manner of growth.

ORDER =GORGONACEA=

SEA-FANS, SEA-WHIPS, AND SEA-FEATHERS

These are compound, tree-like /Alcyonaria/, with a calcareous or

horny skeleton which forms a branched axis and is covered with a

layer of united polyps having spicules of lime distributed through

the mass, which give some firmness to the bark-like covering.

Gorgonias, in great variety, grow in abundance on the coral reefs and

mud-flats of Florida, forming masses of low shrubbery, pink, yellow,

brown, or purple in color.

The sea-whips and sea-feathers are varieties of gorgonias, which are

named from their forms. Some have shapes which resemble branching

shrubs; others are long unbranched rods, either straight or spiral.

They attain a height of several feet and are of various colors. The

colony has a horny axis surrounded by a living mass which resembles a

sheet of animal matter. This mass consists of polyps closely united,

and has throughout its substance spicules of carbonate of lime,

making it a kind of calcareous crust or bark. In dried specimens

this becomes very brittle, and is easily broken from the horny axis.

(Plates XLVI, XLVII.)

[Illustration: PLATE XLVI. GORGONIAS.

Eugorgia aurantica. Muricea specifera. Pterogorgia acerosa. Gorgonia

anceps.]

[Illustration: PLATE XLVII. Leptogorgia rigida (a gorgonia). Eunicea

lugubris (a gorgonia). Gorgonia flabellum (a gorgonia). Leptogorgia

Agassizii (a gorgonia). Pennatula borealis and P. aculeata

(sea-pens).]

The sea-fans are colonies with a central, horny, flexible, and

much-branched axis, covered, as in the sea-whips, with a layer of

united polyps containing spicules of lime, which make a somewhat

[pg153] firm crust. This, in dried specimens, breaks off readily.

The colony branches profusely, or rather separates by fission, in

one plane, the large and small branches making a network of fan-like

shape and often of great fineness and intricacy. These fans attain a

length of several feet and a corresponding breadth, and are abundant

in semi-tropical as well as in more southern waters. In color they

are red, yellow, brown, or purple.

ORDER =PENNATULACEA=

SEA-PENS

These singular colonies resemble quill-feathers, such as are used for

pens, and are named for this reason. The long, horny central axis is

naked below, and is partly buried in the sand, but is not permanently

attached. The upper portion of the axis has two rows of short,

opposite, lateral branches; on the upper side of the branches the

polyps live in separate inclosures. Spicules of lime are present in

the substance of the branches, which gives them stability. Sea-pens

are found at moderate depths and are widely distributed. They are

highly colored and phosphorescent. [pg154]

TABLE SHOWING THE CLASSIFICATION OF THE CTENOPHORA DESCRIBED IN THIS

CHAPTER

Class =CTENOPHORA=

Order =CYDIPPIDA= (/Two tentacles, retractile into sheaths/)

Genera Species

^Pleurobrachia^ ^P. rhododactyla^

Order =LOBATA= (/Numerous lateral tentacles contained in a groove;

body compressed; two large oral lobes/)

^Bolina^ ^B. alata^

^B. septentrionalis^

^B. vitrea^

^Mnemiopsis^ ^M. Leidyii^

Order =CESTIDA= (/Ribbon-like form, from body being extremely

compressed in the vertical plane/)

^Cestum^ ^C. veneris^

Order =BEROÏDA= (/No tentacles; mouth very wide; gullet occupies

greater part of body/)

^Idyia^ ^I. roseola^

^I. cyanthina^

[pg155]

CLASS =CTENOPHORA=

COMB-JELLIES

These are delicate, free-swimming, generally spherical bodies,

resembling jellyfishes in outline, transparency, and gelatinous

consistency, but differing from them widely in the manner of

locomotion. They are called "comb-jellies" from the rows of flat

cilia, arranged like the teeth of a comb, which run in eight

meridional lines over the surface. It is by means of these cilia

that the animal moves through the water. The little paddles are

worked in unison, in single lines, or each one of them can be

moved independently, and they give the animal varying and peculiar

motions. The /Ctenophora/ are nearly transparent, but have a

prismatic coloring, caused by the waving cilia, and at night they are

phosphorescent. They are widely distributed, being found in all seas.

The mouth of the animal opens into a gullet which extends two thirds

through the length of the body. On each side of the gullet is a

vertical tube. The two tubes unite at the base of the gullet, and

from there run as a single canal to the end opposite the mouth, and

open to the outside through two excretory pores. From the base of

the gullet, where the tubes unite, two other tubes extend laterally,

which divide and subdivide in a horizontal plane, becoming eight in

number, and connect at the surface with the lines of cilia; then,

dividing, run in opposite directions to the poles of the spherical

body. The animal derives its nourishment and air through this

circulatory system. A nervous system is situated at the pole opposite

the mouth, in a small area surrounded by cilia, in the center is an

eye-speck, or lithocyst. [pg156]

ORDER =CYDIPPIDA=

GENUS ^Pleurobrachia^

[Illustration: /Pleurobrachia rhododactyla/, in motion.]

^P. rhododactyla.^ A transparent spherical body, one inch to one

and a half inches in diameter, with eight combs or plates of flat

cilia extending from pole to pole. At one pole is the mouth, like

a slit, at the other a small area in the center of which is an

eye-spot. From the body hang two tentacles, half a yard or more

in length, fringed with cilia. The tentacles are very contractile

and can be rolled up or expanded with great rapidity; they take

graceful curves as the animal moves rapidly through the water.

/Pleurobrachia/ has a pink tint, and prismatic colors play over

it from the vibrating cilia. It is a beautiful and interesting

creature to watch. Found along the shores of Massachusetts and

Maine.

ORDER =LOBATA=

GENUS ^Bolina^

[Illustration: /Bolina alata/, seen from the broad side: /o/,

eye-speck; /m/, mouth; /r/, auricles; /v/, digestive cavity; /g/,

/h/, short rows of flappers; /a/, /f/, long rows of flappers; /b/,

/n/, /x/, /t/, /z/, tubes winding in the larger lobes; /i/, base of

gullet. About half natural size.]

^B. alata.^ Slightly oval in form; lower part of the body divided

into two large lobes which hang below the mouth. Four of the

swimming-plates are shorter than the other four and terminate in

curious processes or short appendages called auricles. /Bolina/

is about two inches in length, and is very delicate, transparent,

and phosphorescent. Its contractile power enables it to vary in

outline to a considerable extent. It has a slow undulating motion,

and sometimes carries its lobes uppermost and open. Usually found

associated with /Pleurobrachia/ from Massachusetts northward.

^B. septentrionalis.^ Found on the northern Pacific coast.

^B. vitrea.^ A species found in Florida. [pg157]

GENUS ^Mnemiopsis^

^M. Leidyii.^ Resembles /Bolina/ in general form; often six to

eight inches in length; gregarious, thousands often being collected

together; exceedingly phosphorescent.

ORDER =CESTIDA=

GENUS ^Cestum^

^C. veneris^, Venus's girdle. This singular animal, although not

an inhabitant of our seas, has its place in this group, and is

shown here because of its very curious shape. In form it is flat

and ribbon-like. Sometimes it attains a length of five feet, while

in breadth it is but one or two inches. The mouth is midway in its

length and is opposite the sense-organ or eye-spot. On each side of

the mouth is a short tentacle which protrudes from a sac. Four of

the swimming-plates are small; the other four extend along the edge

of the body. /Cestum/ moves by contractions of the body more than

by the combs which fringe its edges. It is very transparent, with

a violet hue, and is so delicate that it is difficult to capture

it uninjured. Its habitat is the Mediterranean Sea. It may be seen

among the zoölogical specimens in almost any museum.

[Illustration: /Cestum veneris./]

ORDER =BEROÏDA=

GENUS ^Idyia^

^I. roseola.^ This species has an ovate body three to four inches

in height and about half as broad. Some individuals are larger.

It has [pg158] an eye-spot on the upper rounded side, and at

the other end a very large mouth opening into a digestive cavity,

which occupies the greater part of the body. A delicate fringe

surrounds the area about the eye-spot, and eight rows of cilia

run from there to the oral end. It has no tentacles. /Idyia/ is

pink and especially highly colored at the spawning-time. Like

other jellyfishes, their part in life is finished when they have

discharged their spawn, and the first September storms break them

to pieces. In July and August they are plentiful on the New England

coast. They appear at the surface of the water in the hottest part

of the day, but disappear entirely when the water is in the least

rough or the weather is cold or the sun overcast. Their movements

are slow and graceful, the long axis being carried in a nearly

horizontal position. They are exceedingly voracious, feeding

chiefly on other /Ctenophora/, and often swallowing animals as

large as themselves.

[Illustration: /Idyia roseola/, half natural size: /d/, /e/, /f/,

/g/, /h/, rows of locomotive flappers.]

^I. cyanthina.^ This species, found on the northern Pacific coast,

broadens near the center, making it somewhat vase-shaped. /Idyopsis

Clarkii/, a similar genus, found in Florida, is globular. All these

species are very beautiful, the rapid movement of the cilia giving

them a brilliant iridescence.

III

WORMS

(PLATYHELMINTHES

NEMATHELMINTHES

ANNULATA)

TABLE SHOWING THE CLASSIFICATION OF THE WORMS DESCRIBED IN THIS

CHAPTER

Phylum =PLATYHELMINTHES=

Class =TURBELLARIA=

Order ~POLYCLADIDA~

Genera Species

^Planocera^ ^P. nebulosa^

^Stylochopsis^ ^S. littoralis^

^Leptoplana^ ^L. folium^

Order ~TRICLADIDA~

^Planaria^ ^P. grisea^

^Procerodes^ ^P. frequens^

^Bdelloura^ ^B. rustica^

^B. candida^

^Fovia^ ^F. Warrenii^

Order ~RHABDOC[OE]LIDA~

Class =TREMATODA= (/External and internal parasites/)

Class =CESTODA= (/Internal parasites/)

Class =NEMERTINEA=

^Tetrastemma^ ^T. arenicola^

^Nemertes^ ^N. socialis^

^N. viridis^

^Meckelia^ ^M. ingens^

^M. rosea^

^Cerebratulus^ ^C. angulatus^

^Cosmocephala^ ^C. ochracea^

^Polina^ ^P. glutinosa^

Phylum =NEMATHELMINTHES=

Class =NEMATODA=

^Pontonema^ ^P. marinum^

Phylum =ANNULATA=

Class =CHÆTOPODA=

Subclass =Polychæta=

Order ~ERRANTIA~

Families Genera Species

~SYLLIDÆ~

~APHRODITIDÆ~ ^Polynoë^ ^P. squamata^

^P. sublevis^

^Harmothoë^ ^H. imbricata^

^Aphrodite^ ^A. aculeata^

~PHYLLODOCIDÆ~ ^Phyllodoce^ ^P. gracilis^

~NEREIDÆ~ ^Nereis^ ^N. virens^

^N. pelagica^

^N. limbata^

~NEPHTHYDIDÆ~ ^Nephthys^ ^N. ingens^

^N. picta^

~EUNICIDÆ~ ^Marphysa^ ^M. sanguinea^

^Diopatra^ ^D. cuprea^

^Arabella^ ^A. opalina^

^Lumbriconereis^ ^L. tenuis^

~GLYCERIDÆ~ ^Glycera^ ^G. americana^

^G. dibranchiata^

Order ~SEDENTARIA~ or ~TUBICOLA~

Families Genera Species

~SPIONIDÆ~ ^Nerine^ ^N. agilis^

^N. coniocephala^

~CIRRATULIDÆ~ ^Cirratulus^ ^C. grandis^

~TEREBELLIDÆ~ ^Thelepsus^ ^T. cincinnatus^

^Amphitrite^ ^A. ornata^

^Polycirrus^ ^P. eximius^

^Ch[oe]tobranchus^ ^C. sanguineus^

~AMPHICTENIDÆ~ ^Cistenides^ ^C. Gouldii^

~MALDANIDÆ~ ^Clymenella^ ^C. torquata^

^Maldane^ ^M. elongata^

~ARENICOLIDÆ~ ^Arenicola^ ^A. marina^

~SABELLIDÆ~ ^Sabella^ ^S. microphthalma^

~SERPULIDÆ~ ^Serpula^ ^S. dianthus^

^Spirorbis^ ^S. borealis^

Subclass =Oligochæta= (/Mostly terrestrial or fresh-water

forms/)

Class =GEPHYREA=

Order =SIPUNCULOIDEA=

Genera Species

^Sipunculus^ ^S. nudus^

^Phascolosoma^ ^P. Gouldii^

Class =HIRUDINEA= (/Leeches/)

[pg163]

WORMS

Burrowing in sand and mud, lying under stones and in crevices of

rocks, concealed in various kinds of tubular cases which are free or

attached to stones or shells, crawling over the ground or seaweeds,

swimming free or attached to other animals, is found in abundance a

class of animals commonly known as "worms," and generally regarded as

repulsive creatures unworthy of attention.

To the biologist, however, worms are among the most interesting forms

of lower animal life. The amateur collector, if he stops to give

them careful consideration, will probably find them unexpectedly

interesting, and will be surprised to find how many varieties of them

there are, and how different they are from his preconceived notion of

them. Worms are varied in structure, their habits are strange, and

their form and color often beautiful. Although plentiful, they are

not conspicuous, but are easily found if search is made for them, and

so large a class of shore animals should not be passed by unnoticed.

Unusual biological interest is attached to this group because, in the

different types, affinities with other classes of animals are found,

suggesting, perhaps, connecting-links with higher organizations.

They are the first animals to show definite bilateral symmetry, or

two similar sides, and to carry the same part of the body always in

front. Formerly one division, called /Vermes/, comprised all the

worms. To-day they are separated into four divisions, or phyla. The

most careless observer easily recognizes the basis of separation, for

the flatworms, the round- or threadworms, the wheel-like animalcules,

and the jointed worms have very obvious differences. The names given

the phyla express these distinctions, the termination [pg164]

meaning "worm"; the prefixes /Platy-/, /Nemat-/, /Troc-/, meaning

"flat," "thread," "wheel," respectively; while /Annulata/, meaning

"ringed," describes the segmented forms belonging to that phylum.

There are vast numbers of parasitic worms, which live internally or

externally on their hosts, there being no animal of land or sea, of

high or low degree, which is not subject to the affliction of these

visitors. The parasitic worms are degenerate, some being without

digestive organs, or without eyes, or without locomotor organs, and

so on, as the case may be, the host supplying the missing function.

The life-history of these low forms is interesting; but parasitic

worms do not come within the scope of this book, and are mentioned

only to mark their place in the series.

PHYLUM =PLATYHELMINTHES=

FLATWORMS

The flatworms have a flattened body, more or less compressed in the

different classes. Ordinarily the body is very thin, and, when short,

has a leaf-like form; when long it is ribbon-like. Some species are

thick in the middle and thin at the edges. They have a dorsal, or

upper, and a ventral, or under, surface; a right and a left side; an

anterior and a posterior end. The anterior end is carried forward and

has some of the characteristics of a head, though a distinct head is

not apparent. The mouth is on the ventral surface. In some species it

is in the middle of the length of the body; in others it is before or

behind this point.

The flatworms are the first animals to assume pronounced bilateral

symmetry. They are soft-bodied, having no supporting skeleton, and

they have no segments, or divisions, such as are found in higher

types, as in /Annulata/. They have no body-cavity, the space

between the organs and the body-wall being filled with tissue. The

alimentary canal has no anal aperture, the excretions being carried

off by a water-vascular system consisting of branching vessels which

end in minute bundles of vibrating cilia, called ciliary flames.

These flames communicate with the exterior through small pores or

flame-cells. Their sense-organs are eyes [pg165] and otocysts. The

latter are sacs containing crystals of carbonate of lime, and their

function is supposed to be that of hearing.

The flatworms are hermaphroditic, and their propagation is by means

of eggs. They are numerous and very generally distributed, occurring

in fresh and salt water, on land and shore, on the surface and in

the depths of the sea. A vast number also are parasites and infest,

internally or externally, nearly every living creature. The parasitic

forms differ anatomically from the free-living worms. The internal

parasites, living by absorption of the digested food of their hosts,

have no digestive organs; they are also devoid of organs of sense

and of defense. The external parasites, being carried about by their

hosts, are without organs of locomotion.

CLASS =TURBELLARIA=

The turbellarians are the simplest group of bilateral animals and

occupy the lowest place among worms. They owe their name to the fact

that they are covered with cilia, which are constantly in motion and

cause a slight turbulence in the water around them.

ORDER =POLYCLADIDA=

("/Many-branched/")

The polyclads are found below half-tide mark on the under side of

stones and on seaweeds. Sometimes they are found swimming about

at night. They are leaf-like in form, one inch to two inches in

length, and are very thin and delicate. They adapt themselves to the

inequalities of the surfaces to which they attach themselves, and

often are of the same color, and therefore are so inconspicuous that

they are apt to escape notice. They move with a gliding motion over

surfaces, and often swim when in search of food.

The intestine is much branched and has no anal aperture. From the

mouth, which is placed in the center of the ventral surface, a

pharynx, or muscular fold, is protruded in some species, which

enables the worm to attach itself to and consume prey of considerable

size. After digestion has taken place, the fecal [pg166] matter

collects in the main intestine and is forcibly ejected by the

pharynx. Numerous eyes are collected in groups on the anterior dorsal

surface, or arranged around the margin of the body. The eggs are laid

in shell-like cases, and cemented together in plate-like masses or in

spirals, and attached to shells or stones. (Plate XLVIII.)

GENUS ^Planocera^

^P. nebulosa.^ One half of an inch wide and three quarters of an

inch long, circular or elliptical in shape; very flat and thin;

olive-green on the dorsal surface, with a line of darker color on

the posterior end, and whitish retractile tentacles on the back.

Found creeping on under side of stones in tide-pools.

GENUS ^Stylochopsis^

^S. littoralis.^ About one half of an inch long; changeable in

form, from broad oval to elliptical; color pale green, veined with

a lighter shade on the dorsal side, flesh-colored on the ventral

surface; numerous eyes arranged in irregular rows near the margin

and in groups in front of the tentacles, also clusters of eyes on

the tentacles. Found under stones between tide-marks.

GENUS ^Leptoplana^

^L. folium.^ Body flat; margin thin and undulated; shape leaf-like,

but changeable; about one inch long and one half of an inch wide;

color pale yellow, veined with a deeper shade; eyes in four groups

near the anterior end.

ORDER =TRICLADIDA=

("/Three-branched/")

The triclads are divided into three groups: those of the fresh-water

ponds and streams, those of the land and sea, known as planarians,

and those of the sea. The planarians are the most interesting worms

in the order. The triclads differ from the polyclads in being

elongate in form and in having the intestine in three branches

instead of in many. The mouth is midway in the length of the body,

on the ventral side, and from it protrudes a pharynx, which is

cylindrical or bell-shaped, and is capable of great dilatation. With

the pharynx the worm, which is wholly carnivorous, envelops other

worms, crustaceans, or any animal food. Several species are found on

the under side of stones in tide-pools.

[Illustration: PLATE XLVIII. Polyclad worm. Worm-tubes of Diopatra.]

GENUS ^Planaria^

^P. grisea.^ Oval or elliptical in form; anterior end truncate;

posterior end rounded; color yellow or gray, with a light stripe;

two black eyes surrounded with white; length one half to three

quarters of an inch; width about one eighth of an inch. Found under

stones between tide-marks.

GENUS ^Procerodes^

^P. frequens.^ One eighth of an inch long; brown or black above,

gray below; has two kidney-shaped eyes; active and abundant. Found

under stones near high-water mark.

GENUS ^Bdelloura^

^B. rustica.^ Body milk-white, smooth, thin. Found on /Ulva

latissima/ (sea-lettuce).

^B. candida.^ Parasitic on the gills of the horseshoe-crab.

GENUS ^Fovia^

^F. Warrenii.^ Bright red, narrow, oblong. Found on eel-grass.

ORDER =RHABDOC[OE]LIDA=

Minute, active worms found among the red seaweeds. They are brown in

color, and are marked by one or more transverse white bars.

CLASS =NEMERTINEA=

The nemerteans are long, narrow, flat, smooth worms, and vary from

one half of an inch to many feet in length. They are exceedingly

contractile, and when alarmed can shrink to less than half their

normal length. They are very generally distributed, and are to be

found between tide-marks, in loose coils like a string, under stones

on sandy and muddy shores. The very long species, like /Lineus

marinus/, are solitary, but other smaller species are gregarious,

many worms being coiled together in tangled masses. Some species are

to be found in empty shells, and others live among the seaweeds. They

are very slimy, the epidermis secreting an abundance of mucus, and

they can often be tracked by the trail of slime they leave behind

them. This mucus sometimes hardens, forming for some species a

tubular [pg168] covering; others remain naked. All are covered with

vibrating cilia, which is a universal feature of flatworms. In color

they may be white, yellow, green, red, purple, etc., and sometimes

they are banded or striped with a contrasting color. The ventral is

usually lighter than the dorsal surface.

The principal characteristic of the nemertean worms is a long

thread-like organ, known as the /proboscis/. This lies in a sheath

along the center of the dorsal surface, and is quickly thrown out

to a great length, and as quickly completely withdrawn within the

body. The proboscis is slender, hollow, muscular, and full of nerves.

It reaches the outside through a pore at the anterior end of the

body, and has no connection with the alimentary system. It is used

as a feeler and as a weapon. Some species have a sharp spine at the

end of the proboscis, others have stinging-cells. The proboscis is

sometimes so forcibly ejected that it breaks off, in which case it

retains its vitality for some time, and seems as if it were itself a

worm. A new proboscis is quickly grown by the worm to take the place

of a lost one. The head is a little broader than the body, and has

eyes arranged in one or several pairs on each side. The mouth is on

the ventral surface, near the anterior end, has thick lips, and is

very dilatable. Through the mouth the animal ejects a part of the

esophagus and envelops its prey, which is often of considerable size.

Chætopod worms they often swallow whole; the soft parts, after being

digested, are carried off through the regular passages, ending in the

ciliary flames (page 164), while the indigestible parts are ejected

at the anus. Often the spines and bristles find their way out by

perforating the intestine and the body-wall, without apparently doing

the worm any injury. The perforated parts quickly heal.

These worms have the strange power of regenerating lost parts;

mutilated portions are soon repaired. The anterior end, when severed

from the rest of the body, grows again into a complete individual,

while the posterior end continues to perform part of its functions

and retains its vitality for a considerable time before dying. One

species, /Lineus sanguineus/, is capable, after being broken in

pieces, of regenerating each section into a perfect worm. [pg169]

The nemerteans are carnivorous, voracious, and often cannibalistic.

They will live for some time in confinement, losing, however, their

bright color, and the smaller worms will gradually disappear, as they

are devoured by the larger ones. The mode of locomotion varies with

the order. Some species attach their long proboscis to a distant

object, then drag the body to it; some glide rapidly along by means

of the muscles of the body and the cilia which cover it; others swim.

The swimming forms have thin edges which have a wave-like motion,

and this, together with a lateral movement of the tail, propels them

through the water. In some species the worm develops directly from

the egg; others pass through a larval stage before reaching maturity.

GENUS ^Tetrastemma^

^T. arenicola.^ Dark flesh-color or purplish; slender, cylindrical,

four to five inches long when extended; head changeable in form and

partly distinct from body because of slight constriction at the

neck. It lives in sand at low-water mark.

GENUS ^Nemertes^

^N. socialis.^ Individuals very slender, five to six inches long

when extended; color brown or black, a little lighter underneath;

three or four eyes in lines on each side the head. It is abundant

under stones on rocky shores, many coiled together, forming large

masses.

^N. viridis.^ Color olive-green or brown, crossed by faint pale

lines; body changeable in form; when extended, six to eight inches

long, one eighth of an inch or less in breadth; row of dark eyes on

each side of flat head. Common under stones between tide-marks on

northern rocky shores.

GENUS ^Meckelia^