by Lynn Scheu
Even though they are one of the most diverse of all animal phyla,
the Mollusca are usually characterized in the mind of man simply
as "seashells." As colorful, varied and pleasing to
the eye as seashells are, there are also land shells and freshwater
shells, and even snails without shells, to equal them in color
and loveliness. And no matter how wonderful any of these shells
are or what element they inhabit, the soft-bodied animals which
construct them are a part of that beauty and are the cause behind
it. For every shape, size and color, there is a living creature
with a life history.
Conchologists, those people who
study and collect shells, almost always study their animal makers
as well -- their anatomy, their life history and their habitats.
Collecting and studying shells and their makers, the mollusks,
is one of the oldest natural history pursuits of man, dating
back to the Romans and before -- indeed, a shell collection
was preserved in the ruins of Pompeii. Aristotle, and then Pliny
the Elder were among the first naturalists to write about shells
and their peculiar anatomies; in fact it was Aristotle who coined
the name "Mollusca," meaning "soft-bodied."
It was no doubt their versatility
which made mollusks such desirable objects for collection. [See
what Pliny the Elder had say to about shells and their variety
back in A.D. 77] It has been said that shell collecting is the
second most popular collecting hobby, after postage stamps.
Whatever the truth of that, the timeless appeal of shells probably
owes as much to the infinite variety of molluscan shape, color
and pattern as it does to their actual beauty. And man's age-old
fascination for the mysteries of the sea and all of its creatures
is probably responsible for an equal measure of that popularity.
As time permits, this section
will be enhanced with further information on collecting shells.
If you have questions that just aren't answered in the articles
included here, why not post your questions to the Conch-L discussion
group? There you'll meet many conchologists who are willing
Habitats by Dr. Gary Rosenberg
Many people, when they think of collecting shells, picture doing
so on beautiful, white, sandy beaches with the waves
rolling in. However, sandy beaches, especially those with heavy
surf, are not productive habitats for mollusks. Only a few agile
burrowers such as Donax, Hastula and Bullia can survive in the
shifting sands of the surf zone. When a sandy beach has large
numbers of shells cast up in the drift line, this indicates
the presence of more productive habitats nearby.
The stable substrata of intertidal
mud and sand flats have much more diverse communities of
mollusks. They are home to various surface-living bivalves such
as oysters and burrowing bivalves such as soft shell clams,
razor clams, surf clams, Venus clams, cockles, lucines, tellins,
and angel wings. These are preyed upon by carnivorous gastropods
including moon snails, murex, whelks and chanks. Other inhabitants
of mud and sand flats include herbivorous conchs, scavenging
mud snails and deposit feeding ceriths. Mangroves on mud flats
are populated by oysters, periwinkles, ceriths, and ellobiids.
Many of the inhabitants of intertidal
sand and mud flats also occur subtidally, where they
are joined by tusk shells, awning clams, bittersweets, pen shells,
and gastropods such as tons, helmets, harps, olives, volutes,
cones and terebras, Sandy areas can have varying amounts of
rubble mixed in, and often grade into reef flats. Many of the
mollusks found on sand flats also occur in sandy pockets within
the reef, along with miters and ceriths.
Within reefs and rocky
areas live many mollusks that prefer hard substrata. Only a
few kinds of mollusks, such as ovulids (allied cowries) and
coralliophilas, live in direct association with corals, but
the coral rubble around living reefs is rich in mollusks because
it supports luxuriant growth of algae and encrusting invertebrates
on which many gastropods and polyplacophorans feed. Typical
reef-dwelling gastropods include cones, whelks, frog shells,
tritons, cowries, abalones, murex, dove shells, top shells and
turrids. Bivalves include arks, jewel boxes, limas, mussels,
scallops, thorny oysters and giant clams.
Rocky intertidal areas
typically support a rich molluscan fauna. A variety of limpets
are usually present, along with chitons, nerites, top shells
and periwinkles. They feed on vegetation and sessile invertebrates
encrusting the substratum. Muricid snails often occur on intertidal
rocks, where they feed on mussels and barnacles.
See also: Conchology
The above material
has been adapted from Dr. Rosenberg's The Encyclopedia of Seashells,
published by Robert Halt, Ltd., London, 1992. Dr. Rosenberg
is Associate Curator of Malacology at the Academy of Natural
Sciences of Philadelphia