The Marine snails outnumber all of the other mollusks and their shells
are far more beautiful, those in the tropics having the most gaudy
colors imaginable. The animals are all formed on the same plan although
each family has some peculiarity not shared by its relatives. They are
found in all parts of the world, and in all climates. While the majority
of species live either between tides on near low water, there are not a
few which live in the abysses of the ocean and have been dredged at a
depth of three thousand fathoms, a distance of over three miles. The
average depth at which mollusks are found in any number is about one
thousand fathoms. The variability of marine snails is so great that only
a few typical forms can be mentioned.
The Limpet or Patella is a familiar mollusk to many visitors at the sea
shore. This shell is a depressed, conical, oval disk, looking not unlike
a miniature shield. They live on rocks, to which they tenaciously cling.
Some experiments which were made on the English limpet several years ago
showed that they could sustain a weight of thirty pounds attached to
their shell without being pulled from the rock. The animal seems to have
a pretty clear idea of local geography, for it invariably returns to the
same place after its excursions for food and the rock in some localities
has been hollowed out to a considerable depth by the continuous dwelling
thereon of the limpet. If the surface of the rock is uneven the shell
grows in such a manner as to fit these inequalities. While grazing along
the sides of a rock covered with fine sea weed it will leave a track
like a worm and will clear off quite an area in a very short space of
time. This track is made by the radula, which is very long and is thrust
out and loaded with food which it carries to the mouth. When at rest the
radula is coiled like a watch spring. On the British coast the limpet is
used as an article of food and primitive man not only ate the mollusks
but made a necklace by stringing the shells together. There are several
hundred species of limpet-like shells and they are found in all parts of
the world, especially on rocky shores.
A family of shells closely related to the limpets is the Fissurellidæ,
or keyhole limpet, distinguished from the last family by having a slit
or foramen in the apex of the shell, through which the waste products of
digestion are discharged. This slit resembles a key-hole and for this
reason they are called key-hole limpets. The shells of Fissurella are
generally rougher than those of Patella and they live, as a rule, in
warmer seas. In habits the key-hole limpet resembles the limpet, living
in one rocky place and making excursions for food. In the young shell
the spire is without a perforation, this appearing as the shell
increases in age. There are over one hundred species of key-hole
limpets, several handsome species of which inhabit Florida and the West
Indies.
The Haliotis or abalone shells abound in many parts of the world and are
widely known for their beauty. The largest and finest shells live on the
coast of California where they attain a length of ten inches. The shells
are flat, though made in the form of a spiral and are perforated near
the edge of the last whorl, which is many times the size of all the rest
combined, and through this perforation the water from the gills,
together with the waste products of the animal, are poured out. As the
shell increases in size the old holes are filled up and new ones are
formed. The inside of the shell is resplendent with iridescent colors,
particularly about the region of the huge muscle scar, and when the
outside is polished they become objects fit for the palace of a king. A
large part of the mother-of-pearl is furnished by these shells and a
vast number are annually exported for the purpose of making pearl
buttons. In England they are called “Ormers” but the correct name, if we
translate the generic title, is “Sea-ear” or ear-shells. To the Chinese
the abalone is an object of great economic importance and they gather
them in large quantities, dry the animals and use them as food,
principally in the form of soup, which is said to be very delicious. The
abalone clings to the rocks with terrible power and many a lonely
fisherman has been drowned while gathering this mollusk, by getting his
fingers caught between the shell and the rock.
[Illustration: SOME SNAILS OF THE OCEAN.
FROM COL. CHI. ACAD. SCIENCES.]
Top row:
Strombus puris dianae (Philippines).
Bulla ampulla (Philippines).
Harpa nobilis (Philippines).
Second row:
Littorina angulifera (United States).
Fissurides listeri (United States).
Third row:
Nerita peloronta (Florida).
Crepidula fornicata (United States).
Terebra lamarckii (Sandwich Islands).
Turbo petholatus (Indian Ocean).
Fourth row:
Nitra politificalis (Indian Ocean).
Haliotis assimilis (California).
Cerithalma aluco (East Indies).
There are three families of shells which are much sought after by
conchologists, these are the top shells (Trochidæ), the turban shells
(Turbinidæ) and the pheasant shells (Phasionellidæ). Altogether they
embrace nearly five hundred species which live from the shore between
tides to the lowest depths of the ocean. The shells of the top shells
vary to a wonderful degree; some are large, others small; some are
perfectly plain and smooth while others are ornamented by impressed
lines, ribs and granules, some are very thin and delicate while others
are large and massive. Many of the species are richly colored with
brown, purple, black, green and yellowish, and all are more or less
pearly. They are all vegetable eaters.
One of the best known is Trochus niloticus, a large, massive shell
striped with brown, which is seen on the mantle of many households. One
of the prettiest top shells is the ringed top shell (Calliostoma
annulatum) found abundantly in some parts of California. The surface is
marked by several rows of delicate points and the suture is bordered by
a rich line of purple. It lives in the seaweed off shore and may be seen
in pleasant weather crawling about among the weeds. During storms or
rough weather this frail mollusk sinks to the bottom of the sea. The top
shells inhabit many parts of the world, the coasts of Florida and
California producing several very handsome and interesting species.
The Turban shells include many fine and large shells, a notable species
being Turbo marmoratus, the “green turban” of the dealers. This shell is
about seven inches in diameter, rich green outside and pearly inside. It
is largely used for mother-of-pearl work and for making pearl buttons.
It is said that the early Scandinavian monarchs used this shell as a
drinking cup. At the present time it is used for ornamental purposes,
richly mounted. In Japan the animal is used for making chop suey, being
cut in little dice-like pieces.
The Pheasant shells are beautifully variegated with red, black, white
and brown and are very interesting animals to study alive. When
crawling, the left side of the foot moves forward while the right
remains stationary, and when the right side moves the left remains
stationary. This curious mode of progression has been likened to the
canter of a horse. The larger species, with beautifully variegated
shells, inhabit Australia, while the smaller species live in the
Mediterranean Sea, South Africa, the West Indies and California.
The Neritas are very abundant in tropical and semi-tropical countries
where they live on rocks and stones near low water mark. They are said
to be nocturnal and spend the night feeding on seaweed. The shell of the
Nerita is solid and heavy and variously ornamented with ribs, pustules
and color patterns. The “bleeding tooth shell” (Nerita peloronta), so
named from the presence of a red spot near one of the columella teeth,
is a typical member of this genus. A species living in the Philippine
Islands is said to climb trees to a considerable height.
The family Cerithiidae comprises some very handsome shells which inhabit
salt, brackish and fresh water. They are found throughout the world but
the finest species live in the tropics. The spire is very long and is
composed of many whorls. Some shells are smooth and polished, while
others are marked by frills, knobs, spines and ribs. The name Cerithium
is from the Greek word ceration, meaning a small horn, and is used
because of the horn-like shape of the shell. This family has its giants
and also its pygmies, the latter being pretty, reticulated shells from
one fourth to three fourths of an inch in length, living among the eel
grass and other vegetation along the shore. There are over a hundred
species of these small shells, and some when handled discharge a bright
green fluid.
Whoever visits the seashore is bound to become intimately acquainted
with the Littorinas, or periwinkles, for they cover the rocky shores
everywhere, millions of their rounded shells clinging to the rocks when
the tide goes out. They feed on the algae which grows on the shore. They
are found in both brackish and fresh water. The common periwinkle
(Littorina littorea) is extremely abundant on the shores of southern
Europe and the northern part of the United States. In England it is used
as an article of food and it is said that nearly two thousand tons are
gathered annually and that a thousand persons are employed in capturing
it. In London and other large cities they are sold on the street, the
animal being picked out with a pin. It is used for bait in some of the
fisheries and the oystermen plant many bushels on their oyster beds
yearly to keep the seaweeds from accumulating. From these facts it will
appear that this periwinkle is of considerable economic importance. All
of the species are amphibious, living for a long time out of the water.
Of all the gastropods none excel the curious Xenophora in point of
oddity. The shell is in general form like that of the top shell, but as
it grows it attaches to itself small stones and pieces of shell, so that
when the animal is fully grown it looks like a heap of dead shells and
pebbles. This habit is in all probability to conceal the animal from its
enemies. They are called “carriers” and the individuals with shells
attached to their house are called Conchologists, while those with
stones attached are called Mineralogists. The fragments of shells are
attached with concave sides upward so as not to impede the animal during
locomotion. The carriers are not able to glide like other mollusks,
their feet being very small. They progress by lifting the front part of
the foot to an object and then drawing the hind part toward it. In this
way they jump or scramble along in a ludicrous manner.
Related to the “carriers” are the slipper-shells (Crepidula), the
horse-hoof shell (Hipponyx) and the bonnet-limpet (Capulus). The slipper
shells are found in many parts of the world and are particularly
abundant on the Atlantic and Pacific shores of the United States. The
shell is flat and somewhat limpet-like, and across one end, near the
apex, is a little shelf which gives it the appearance of a Chinese
slipper. They adhere to stones, shells, crabs and any submerged object,
and modify the form of their shell to fit the inequalities of their
resting place. Thus a Crepidula on a Pecten shell will be ribbed while
the same species on a stone will be perfectly smooth. Frequently they
may be seen piled one upon another in tiers of six or more. The animal
generally feeds on seaweed but has been known to eat other mollusks. The
bonnet limpets also belong to this family, as do the cup-and-saucer
limpets (Calyptraea).
The family Strombidae contains many large and interesting shells. The
animal is very powerful and is able to leap a considerable distance. Mr.
Arthur Adams, a celebrated conchologist, thus describes its method of
leaping: “Planting firmly its powerful, narrow operculum against any
resisting surface, it insinuates it under the edge of its shell and by a
vigorous effort, throwing itself forwards, carrying its great heavy
shell with it, the animal rolls along in a series of jumps in a most
singular and grotesque manner.” The eyes of the animal are greatly
developed. The shells of Strombus vary greatly in form and color. In
some the outer lip is simply turned over while in others it is modified
by little spines or projections. The aperture is frequently colored
pink, purple or yellowish. The large Strombus gigas is used in carving
cameos, its shell being made up of several layers of different colors.
It is also ground to powder for the manufacture of porcelain and in the
West Indies the animal is used as an article of food.
The Auger or steeple shells, belonging to the family Terebridae, have
long been objects of interest not only to the naturalist but to the
layman who places them in his house as ornaments. There are about two
hundred species which are found in many parts of the world, although
chiefly confined to tropical seas. The shells are very long and are
composed of many tightly wound whorls, which are smooth in some species
and longitudinally ribbed in others. They vary also in color, being
yellowish, grayish or brownish, and many species are spotted with red or
white.
A group of handsome mollusks live in the tropics whose shells have been
named Mitra by the naturalist Lamarck from their fancied resemblance to
the Pope’s miter. The shells are fusiform, very thick and heavy and
beautifully ornamented with various colors. The surface of the shells of
some species is smooth, others granulose and not a few spirally lined
and longitudinally ribbed, while the columella is marked by several
heavy plaits or folds. There are about two hundred species of this
genus, living in all parts of the world but being more numerous in
tropical regions. The Philippine Islands seem to be the metropolis of
this mollusk, as of others, and their shores fairly teem with the
graceful creatures. Some of them live among the coral reefs, concealing
themselves in holes or among the sea weeds or under stones. Others live
on the sandy or muddy beaches in which they bury themselves when the
tide recedes.
The earlier naturalists were fond of applying significant names to the
shells which they described and the Mitras have received their share.
Thus we have the episcopal miter, having a white shell with brilliant
red spots and flame; the papal miter, with a brown-spotted white shell;
the pontifical miter, with a red-spotted shell and a coronated spire,
and lastly the cardinal’s miter. These four species might be called the
ecclesiastical quartette.
The Harp shells, although few in species, are among the most showy of
the marine snails. The shells are large and marked by many elevated ribs
extending longitudinally, giving the effect of the strings on a harp,
hence the name of the genus. The colors are different shades of brown
which form neat festoons of dark brown lines between the ribs. The inner
lip of the shell is marked by a dark brown spot and another spot is
frequently developed near the upper part of the whorl. In one species
(Harpa rosea) the shell is marked by several rosy spots and tints, and
is very beautiful. The animal of this genus is no less interesting than
the shell, being variegated with many beautiful colors. The foot is
long, crescent shaped in front and becomes narrowed to a point behind.
The animal is said to voluntarily break off a piece of its shell when
irritated, as it is not able to retreat within the shell, being
destitute of an operculum. It is very active and crawls about with an
easy, graceful motion. Harpa lives only in the tropics and is found in
the Indian and Pacific Oceans and on the west coast of America.
The Bubble shells include within their number many curious and
interesting animals. The typical genus, Bulla, numbers some fifty
species of smooth, globular shells, frequently mottled like a bird’s
egg. The aperture is as long as the shell and the outer lip is thin and
sharp. The animal is large and fleshy and partly envelops the shell. The
bubble shells love sandy mud flats in which they bury themselves or find
concealment under masses of sea weed. Like many land shells they exude
vast quantities of mucus to moisten their skin when the tide is out.
These animals are carnivorous, living on bivalves and snails, which are
swallowed whole and reduced to fragments by the huge, calcareous
gizzard. Not all the mollusks of this order have true shells. The
so-called sea hares, have large, flabby bodies in which is lodged a
small, oblong, transparent shell. This animal lives among the sea weed,
feeding upon the weed as well as upon mollusks and other animals. It
discharges a violet liquid when handled which caused the ancients to
believe that it was poisonous. The old Greek philosophers wrote a great
deal on this subject, believing that to even touch the animal with a
stick would cause death. Though repulsive looking creatures they are
perfectly harmless and are even eaten raw by the natives of the Friendly
and the Society Islands.
Frank Collins Baker.