50,000 or more species of molluscs. Characteristics:

Bilateral symmetry. Body enclosed by a blanket-like mantle that

secretes a shell made of calcium or some other stiff structure.

A mantle cavity between the mantle and the internal organs; the anus, reproductive, and excretory ducts open into the mantle cavity.

A ventral, muscular foot that is highly modified among the various groups of molluscs.

Head withy sensory organs and a mouth.

Characteristics: Aquatic mollusks have gills. Terrestrial mollusks

have lungs. Herbivorous or carnivorous. All of them with a

complex digestive system. Most of them are hermaphrodites. In separate sexes individuals, there is no sexual

dimorphism. Most of them lay eggs from which a larvae

emerges. It will go under metamorphosis. Have a true heart Simple to complex nervous system

Some mollusc habitats include: Marine (mostly) Freshwater (a few) Land (a few)

Mollusc niches (life-style): Most live on the ocean bottom and are

mostly sedentary Some are free-swimming (the

cephalopods)

There are seven mollusc classes. We will study 3 of them: Gastropoda (gastro=body cavity;

poda=foot) Ex. Common garden snail, limpets

and slugs

There are seven mollusc classes. We will study 3 of them: Gastropoda (gastro=body cavity;

poda=foot) Ex. Common garden snail, abalone,

turban snail Bivalvia (bi=two; valvia=valves)

Ex. Clam

There are seven mollusc classes. We will study 3 of them: Gastropoda (gastro=body cavity;

poda=foot) Ex. Common garden snail, abalone,

turban snail Bivalvia (bi=two; valvia=valves)

Ex. Clam Cephalopoda (cephalo=dealing

with head; poda=foot) Ex. Squid, octopus, sepia, nautilus,

etc.

LIMPET SLUG SNAIL

Most popular class of molluscs. Consists of snails and snail-like creatures. Specific characteristics:

They have a dorsally located shell (often coiled).

They have a well-developed radula. 4 tentacles (2 optic and 2 sensory)

Most popular class of molluscs. Consists of snails and snail-like creatures. Specific characteristics:

They have a dorsally located shell (often coiled).

They have a well-developed radula. 4 tentacles (2 optic and 2 sensory)

Visceral mass (organs) almost always located inside the shell. Their visceral mass is rotated 180 degrees during development.

They are herbivores or predatory (carnivorous).

Habitats include: ocean, lake, river bottoms, coastal shores, and land. Terrestrial have lungs and aquatic have gills.

MUSSEL CLAMCOCKLE

SWORD RAZOR

They have no head. They have two shells held

together by powerful muscles.

They have a ventrally located foot that sticks out between the two valves.

They tend to burrow into soft mud or sand or attach to rocks or other shells.

Habitats include: marine and freshwater.

Large gills are used for respiration and filter feeding.

Water enters and exits through siphons.

OCTOPUSNAUTILUS SEPIA

SQUID

Contains the largest molluscs. Specific Characteristics:

May lack a shell (like an octopus) Shell may be reduced to a stiffening rod (like the

squid or nautilus) The foot is highly modified to form a group of

tentacles around the mouth. They are found in deep and shallow waters along

many coasts. Squids & Nautilus are free-swimming and move

very quickly. Octopuses are found among rocks or crawling on the bottom of the ocean.

Complex brain, two lateral eyes, excellent eyesight.