Many of my readers have doubtless spent some of the vacation months at
the sea shore and have wandered over the beach at low tide picking up
shells and other objects left by the receding ocean. They have also, I
am sure, peered into the little pools of water left on the beach and
have watched with interest the captives imprisoned therein, hermit
crabs, fiddler crabs, sea anemones, sea worms and snail shells. It is
with the latter that the present article will deal.
The stretch of beach which is uncovered twice a day by the receding of
the water is called “between tides,” and is inhabited by a host of
animate creatures, chief among which are the mollusks. The marine snails
outnumber all of those which we discussed in the last article, and their
shells are far more beautiful, those found in the tropics having the
most gaudy colors imaginable. The animals are formed on the same plan as
those of the fresh-water snails, although each family has some
peculiarity not shared by its relatives. All live in the water and
breathe air through that medium by means of gills, similar to the second
class of fresh water snails mentioned in the last number. They are found
in all parts of the world, those of the tropics, however, being the most
brilliantly colored. While the majority of species live either between
tides or near low water, there are not a few which live in the abysses
of the ocean, and have been dredged from the bottom of the sea at a
depth of two thousand, seven hundred and forty fathoms, or, to put it
more plainly, 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 we shall be able to call attention to but
a limited number of typical forms.
Among the best known of the marine snails are the Tritons, a family of
mollusks living in tropical seas. Their shells are generally large and
highly-colored and variously ornamented with short spines and knobs. One
species, the Triton tritonis, is among the largest of mollusks,
measuring eighteen inches in length. One of the smaller Tritons is
pictured on the plate. Another shell familiar to those who have visited
Florida is the Fasciolaria or banded snail, which attains a length of
three inches and is very prettily banded and dashed with color. A near
relative of this species is the giant banded shell (Fasciolaria
gigantea), which is the largest of all marine snails, growing to a
length of nearly two feet. This species is found plentifully on the
southern Atlantic coast of the United States, being particularly
abundant about the coral reefs of the Florida Keys.
A genus of mollusks with light horn colored shells, and inhabiting the
cold waters of the Arctic seas, is the Buccinum, or whelk. In various
parts of Great Britain it is known as “buckie” and “mutlog.” The
Buccinum delights to burrow in the sand, like the moon shells (Natica),
and frequently nothing but the end of the siphon can be seen, the latter
protruding from the sand to enable the water to enter the animal to
furnish the necessary oxygen. The whelk is used economically, both for
food and bait. One ingenious method of catching them is to fasten a dead
fish of good size in a wire basket and to allow it to rest on the bottom
for a short time; when taken up it is covered with large, fat whelks.
This fishery in Great Britain is fully as valuable as our oyster
fishery, the annual income from this industry reaching to thousands of
pounds sterling. The animal is also one of the principal baits used in
cod fishing. A related genus, the neptune shells (Neptunea), is also
eaten by the poorer people and makes a good codfish bait. The two kinds
of whelk (Buccinum and Neptunea), are termed, the first the white whelk
and the second the red or almond whelk, probably on account of the
colors of the two shells. In the Shetland Islands the red whelk is used
as a lamp, being suspended by strings from a nail, the mouth placed
uppermost and filled with oil.
[Illustration: ]
First row:
Cypraea pantherina (Red Sea)
Cassis flammea (Bahamas)
Conus marmoreus (Polynesia)
Second row:
Buccinum undatum (U. S.)
Fasciolaria distans (U. S.)
Third row:
Tritonium olearium (Naples)
Oliva irisaus (Amboina)
Voluta musica (West Indies)
Fourth row:
Ianthina communis (Atlantic Ocean)
Chiton squamosus (Jamaica)
Lottia gigantea (California)
Nassa glans (Amboina)
The basket shells or dog-whelks are among the most numerous in
individuals of all the marine snail shells, the common black whelk
(Nassa obsoleta) being the most common of all the mollusks. The writer
has seen a mud flat at low water literally paved with the shells of this
snail, there being millions of the little creatures crawling about. The
shells of this family are frequently very handsome, being latticed by
the crossing of lateral and longitudinal lines. They are mostly of small
size, scarcely exceeding an inch in length, many of them being much
under these dimensions. The animal is very rapid in movement and leaves
a distinct track in the mud, which will frequently end at a little
pellet of mud, which, upon examination, will disclose the little animal
nicely concealed beneath.
The Nassas of France are very destructive to the oyster beds of that
nation, an adult “borer” being able to perforate the shell of a large
oyster in a single night. So numerous are these pests that a single acre
has yielded over a thousand individuals. As a result of these
depredations the French oystermen carry on a relentless war against the
Nassa, destroying thousands of animals annually. With all this
persecution the mollusk still exists and even increases in numbers. The
dead shells of this genus are a favorite home for the hermit crabs of
small size, and it is to be suspected sometimes that other than dead
shells are appropriated. We fear that a sort of piracy is resorted to by
the hermit crab, resulting in a kind of “walk-the-plank” end for the
mollusk, before the new tenant takes possession of the “home.”
Of the many varieties of tropical shells, few exceed the Volutes, or bat
shells, in beauty or variety of coloration. They are found in most parts
of the world, although strangely enough none are now living in the seas
of Europe, but they are most abundant and more highly colored in the
tropics and subtropics. The animal is carnivorous, and the long,
fang-shaped teeth are certainly suggestive of predaceous habits. The
shells are variously colored, some being mottled, some with zigzag or
lightning-like markings, while others have spirally arranged dots and
lines. One species (Voluta musica, figured on the plate), has received
its name from a more or less fanciful resemblance of the surface of the
shell to a musical staff, the spiral lines being grouped in sets of four
or five and the dots being arranged as notes. In some specimens this
resemblance is quite close. The smooth and polished shell of some
volutes is due to the fact that the greater portion is covered by a
reflected part of the large foot.
On the sandy shores of subtropical beaches certain graceful and polished
animals bury themselves from sight in the sand. These are the olive
shells (Oliva) whose bright colors and highly polished surfaces rival
even the gaudy Volute in beauty. The foot may be described as
plough-shaped and is admirably adapted for digging rapidly in the sand,
so that the shell may be hidden from sight on the approach of enemies.
The long siphon is thrust up through the canal in the anterior part of
the shell and its end protrudes above the sand. The high polish of the
surface is due to the shell being enveloped in the voluminous foot;
hence it has no epidermis. The aperture is so narrow that it is
difficult to understand how the animal gets in and out. The olives are
very numerous in individuals; when one is found hundreds are sure to
reward a patient search.
Probably no more distinct family of mollusks exists than the Conidae,
the family of cones, their beautifully decorated shells and the large
number of species making them a favorite with collectors. The shell is
in the form of an inverted cone, gracefully rounded, the aperture being
but a narrow slit extending nearly the whole length of the shell. The
colors of the cones are always very brilliant, although when they are
alive the shell is not brilliantly polished as the olives, on account of
the presence of an epidermis. About three hundred species are known,
living principally in tropical seas. They love to conceal themselves in
holes in the rocks and among the branches of corals. The animal is
predaceous, boring into the shells of other mollusks and extracting the
juices from the bodies. The teeth of Conus are hollow and very sharp and
have a barb on the end. A poison gland is said to be present in this
genus and bites from the animal are very painful, although not
dangerous, the large Conus marmoreus being able to inflict a severe
wound. The cone is quite pugnacious and will immediately bite the hand
when picked up, a veritable reptile of the ocean.
The ne plus ultra of mollusks to the collector is without doubt the
genus Cypraea, comprising the cowry shells. So eagerly have they been
sought by wealthy collectors that the price of rarities has gone up to
an astonishing degree, some specimens being sold at several hundred
dollars each. The shell is highly polished, owing to the fact that two
lobes of the voluminous mantle are turned back over the shell and meet
in the middle of the back. The foot is very large and spreading, the
mantle beset with curious little tentacular-like organs and the eyes are
placed on small swellings near the base of the long, cylindrical
tentacles. The color-patterns of the shell vary to a wonderful degree.
The young shell has a thin epidermis, a sharp lip to the aperture and a
more or less prominent spire, the rolled over and toothed lip and
polished surface not being acquired until fully adult. No more beautiful
sight can be imagined than one of these gorgeous animals, as seen
through the clear water, crawling over the sandy bottom or on the branch
of some coral.
Several of the cowries have a curious economic value. Thus, Cypraea
aurantia, the orange cowry, was used as an insignia of royalty by the
chiefs of the Friendly Islands, and for a long time the only specimens
obtainable were those which had been bored and used. The money cowry
(Cypraea moneta) has been used as money by the natives of Western
Africa, and many tons of this small shell were annually imported to
England to be used in barter by the African traders. The shell is of a
yellowish or whitish color, does not exceed an inch in length, and is
very common in the Pacific and Indian Oceans. It is still used as a
medium of barter in parts of Africa, although other things have pretty
generally taken its place.
Cameos were at one time quite in the fashion, both as ornaments for the
person in the way of brooches, and as bric-a-brac about the room. These
shell-cameos are made from the genus Cassis, the helmet shells. These
are well adapted for this purpose, as the shell is made up of several
differently colored layers, making a bas relief figure not only possible
but very effective. The black helmet (Cassis madagascariensis) is one of
the best for this purpose, the figure being carved from the white, outer
layer of shell, which stands out very clearly against the black
background of the second layer. When a cameo is desired simply as a
brooch or for any other form of personal adornment, a piece of the shell
is cut out and shaped into the required form and size—oval, square or
other shape—and cemented to a block of wood. The figure is then traced
on the shell with a pencil and finally carefully worked out with sharp,
pointed steel instruments, of delicate size and form. The same process
is resorted to in working out a bas relief on the entire shell, only the
latter is placed in a vice or other object to hold it firmly. The home
of this industry is Genoa and Rome, Italy, although some are produced in
France; these latter, however, are of a poorer quality. Several thousand
people are employed in this trade. Many beautiful examples of this work
were exhibited at the World’s Columbian Exposition, in Chicago, in 1893.
The cameo shells are among the largest of sea snails, several of them
measuring eight or ten inches in length and weighing several pounds.
They are found only in tropical and subtropical seas, living in
comparatively shallow waters on a sandy bottom. They are voracious
eaters, living principally on bivalve mollusks.
One of the most abundant of mollusks is the violet sea snail (Ianthina
communis), which spends its life floating in the waters of the Atlantic
Ocean. The shell is very delicate, resembling in form some of the land
snails, and has but two colors, both shades of violet, a deep color on
the under side (which, by the way, is always turned upward when the
animal is floating in the water), and a lighter shade on the upper side.
So fragile is the shell that it seems as if a breath would break it. The
most interesting fact in connection with this mollusk is the wonderful
float or “raft” which is secreted by the foot, and to the under side of
which the eggs are attached. The latter are not all in the same
condition. Nearest to the animal they are more or less fresh; those in
the middle of the float contain embryos and fully formed young, while
those on the outer end are empty, the young having escaped into the
water. The genus is gregarious and may be found in almost countless
numbers. After a severe storm they are sometimes cast upon the beaches
in vast numbers, where they soon die under the fierce rays of the sun.
We have thus far been dealing with snails whose shells were formed in a
spiral coil. Quite a number of mollusks are not protected by such a
shell, its place being taken by a flat, shield-like disk, or several
distinct plates placed side by side. The most familiar of the first is
the limpet or Patella, which is a depressed, conical, oval disk, looking
not unlike a miniature shield. They live on rocks, to which they cling
with great tenacity. 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. The large foot is very strong and it is almost impossible to
dislodge the shell from the rock when the animal becomes alarmed and is
aware that danger is near. While grazing along the sides of a rock
covered with fine sea-weed, it will leave a track like a worm and will
clean off quite an area in a very short space of time.
Another species is the key-hole limpet (Fissurella), distinguished by
having a slit or foramen in the apex of the shell. The shells of
Fissurella are generally rougher than those of Patella, and as a rule
they live in warmer seas. In the limpet we find a departure from the
general form of both animal and shell, both being bilaterally
symmetrical, that is, having both sides alike. In the mollusks which
have been presented thus far, the body has been twisted in the form of a
spiral, making one side different from the other and causing the organs
of one side to become atrophied. In the limpets the organs are paired,
as they are supposed to have been in the ancestors of the living
mollusks.
The most peculiar of all the mollusks, so peculiar, indeed, that they
constitute a separate order (Polyplacophora) are the Chitons, or
coat-of-mail shells. The shell is made up of eight separate pieces or
plates, each locking with the other, the whole supported by and buried
in a coriaceous mantle which forms a margin all the way around. This
must not be confounded with the true mantle of the animal, for it is
only a part of the shell. It is beset with bristles, spines or hairs,
which add much to the peculiar appearance of this mollusk.
The Chitons live for the most part on rocks at low water and are said to
be nocturnal in habit, feeding only at night. Their movements are slow
and they appear to be very sluggish in all their actions. When detached
and taken from their rocky homes they have the provoking (to the
collector) habit of rolling up and are sometimes very difficult to
straighten out again. There are about two hundred and fifty living
species, found in all parts of the world.
In the foregoing pages we have called attention to a few types of marine
snails, and what has been written has hardly more than touched upon this
vast field. There are thousands of different species even more
interesting than those which have been mentioned. There are the
beautiful ear shells, or Abalones, the little periwinkle, so largely
used as an article of food in Europe, besides a host of others too
numerous to mention. The brief notes and the figures on the plate will
convince the reader, it is hoped, that these inhabitants of the deep are
not only beautiful and worthy of our attention and study, but are also
of much practical and economical use to man.
Frank Collins Baker.