Transcript “foot” is divided into sucker-bearing arms, or tentacles

Major Groups of Mollusks
The mollusks represent a diverse group of marine, freshwater, and terrestrial
invertebrates, including such varied forms as snails, chitons, limpets, clams, mussels,
oysters, octopuses, squid, cuttlefish, tusk shells, slugs, nudibranchs, and several highly
modified deep-sea forms. They all have one anatomical feature in common, the
presence of a shell at some stage in the life cycle. Although most mollusks have a shell
as adults, the octopus, squid, and deep-sea forms do not. They do however have a
small, shell-like structure, called a shell gland, present for a short time during embryonic
development
Chiton
Chitons range in length from less than 2.5 to 30 cm (1 to 12 in), but all sport a coat of
mail made of eight jointed, symmetrical shell plates. This flexible structure enables the
animal to roll into a ball if its muscular foot becomes detached from the rock to which it
clings.
Gastropod Anatomy
The development of a coiled shell and the process of torsion, or the systematic twisting
of the body over time, led gastropods to evolve from bilateral to assymetrical body
structures. This diagram shows the generalized internal anatomy of a gastropod.
Snail Anatomy
The development of a coiled shell and the process of torsion, or the systematic twisting
of the body over time, led snails to evolve from bilateral to assymetrical body structures.
This diagram shows the generalized internal anatomy of a snail.
Snail
Some groups of snails have shells that coil to the left (left-handed), while others have
shells coiling to the right (right-handed). In some groups both right- and left-handed
members are present. The shell affords protection from predators and the rigors of the
environment. When threatened, the snail pulls its entire body inside. A small, circular
structure called the operculum closes securely behind the snail to form a tight seal that
keeps out predators and keeps in moisture.
Tortoiseshell Limpet
The tortoiseshell limpet is a species of limpet common to waters off the northeastern
coast of the United States. Limpets, single-shell marine gastropods, live along rocky
coasts all over the world. Most limpets cling to rocks while grazing for food, usually
algae. Some limpet species are consumed by humans while others are used as fishing
bait.
Cone Shell
The cone shell is one of 400 to 500 cone species of mollusks that can be harmful to
humans. Cones are carnivores, equipped with powerful nerve poisons. They search out
prey with a muscular, retractable proboscis that carries a mouth, a salivary gland, and
teeth.
Sea Slug
Lacking the external shell that typifies other gastropods, sea slugs such as the lavender
species pictured here have evolved other mechanisms of defense. The coloration of
some matches their environment to camouflage the animal from predators. The tissues
of others contain foul-tasting substances, prompting any inexperienced captor to spit
them out quickly and avoid their often bright pigmentation the next time
Sea Slug Sea slugs are marine gastropods that have adapted without a main feature of
the gastropod family, a shell. Most sea slugs move with their single foot by using waves
of muscular contraction. They are the largest species of the gastropod family, weighing
up to 13 kg (about 29 lb).
California Sea Hare Sea Hares are mollusks that inhabit shallow ocean waters around
the world. Their prominent tentacles are sensitive to touch and smell. When threatened,
certain species squirt purple ink to form a protective cloud.
Bubble shells are mollusks with a thin, sometimes colorful shell. They live in shallow
marine waters in temperate zones
Generalized Anatomy of a Mollusk
There are around 50,000 species of mollusks, ranging from tiny snails less than 1 cm (0.25 in) in length to giant
squids, which reach a length of 18 m (60 ft). Despite this great variation in size, most mollusks have the same
basic body structure. Most mollusks have a glandular body covering, called the mantle. In some mollusks, such as
clams and snails, the mantle secretes a hard shell. Most mollusks have a large muscular organ, called the foot,
which is used for burrowing or for moving over the ground or sea bottom. Many mollusks feed by means of the
radula, a flexible organ that bears many sharp teeth. Mollusks use gills to absorb nutrients from water and release
waste products from cells.
Mussel
A view of the interior of a mussel shell reveals the mussel’s visceral mass containing the
gills and internal organs. The circular white structure at the upper right hand corner of
the visceral mass is the adductor muscle, which helps to keep the shell tightly sealed
against predators or during low
The prominent growth rings found on the outer surface of the clam shell are useful in
determining the clam’s age.
Scallop
Scallops are bivalve mollusks related to oysters, clams, and mussels. The circular white
muscle tissue dominating the interior of the shell has a flavor and texture that makes the
scallop one of the most prized of all seafoods.
Generalized Anatomy of an Oyster
Enclosed within a thick, sturdy shell, the soft body of an oyster is adapted for filtering minute
planktonic organisms from the surrounding water. The gills filter and collect food that the stomach
then digests. The mantle is a thin membrane that covers the body and lines the inside of the shell.
The adductor muscles and the hinge between the two halves of the external shell help keep the
shell closed
Close-up of a Mussel This close-up shot of a mussel shows its mouth and
the muscle tissue surrounding it.
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Giant Clam
The giant clam, which lives on coral reefs in the Indian and Pacific oceans, is the
second-largest extant mollusk, weighing up to 227 kg (about 500 lb) with the shell. The
giant clam feeds on marine bacteria. The bright-blue giant clam here has burrowed into
the ground, as many clams do.
Pearls in Shell Pearls are valued as gemstones although they are not actually minerals.
They are made from the same material that covers the inside of mollusk shells, an
iridescent substance called nacre, more commonly known as mother-of-pearl. When an
irritant such as a parasite enters its shell, a mollusk secretes a nacre coating to make
them less dangerous to its soft tissues. Eventually, the nacre coatings transform the
irritant into a pearl.
Zebra Mussel
Accidentally introduced from Europe in the mid-1980s, zebra mussels have spread
throughout many North American lakes and rivers. These hardy freshwater mussels
grow and reproduce quickly. They attach to almost any submerged surface, frequently
coating or clogging boat hulls, fishing equipmen
Generalized Anatomy of a Squid
The squid, a representative cephalopod, shows several variations on the mollusk body plan. With a
name meaning “head-footed,” the cephalopod’s “foot” is divided into sucker-bearing arms, or
tentacles, specialized for drawing food into the animal’s beaklike jaws. Another cephalopod
adaptation is the mantle. Highly muscular, it forces water from the cavity through the tubular
siphon to propel the animal quickly through the water. Most notable perhaps is the internal shell,
greatly reduced from the large external shells of other mollusks. This shell is entirely absent in
octopuses.
Cuttlefish
The cuttlefish is an open water, or pelagic, species that swims using its marginal fin.
Cuttlefish feed on fish and invertebrates and are themselves the object of commercial
fisheries in many parts of the world. Cuttlebone, a supporting rod of calcium carbonate
found only in cuttlefish, is used as a polishing agent as well as a calcium and salt
supplement for captive birds and other animals
Chambered Nautilus
A cutaway view of the shell of the chambered nautilus reveals the compartments that
housed the nautilus when it was smaller. These smaller chambers, now connected
together by a small calcified tube, regulate the buoyancy of the nautilus as it swims
along. The compartments are filled with nitrogen gas, which is produced by the nautilus.