Phylum Mollusca the “mollusks”

General Characteristics Have a soft body sometimes enclosed in a shell Have a ventrally located muscular foot used for movement The larvae stage is called a trochophore – microscopic and free swimming often not resembling the adult Considered coelomates – meaning they have a fluid filled body cavity (coelom) Have a specialized organ called a radula which is used to scrape food off of hard surfaces

Feeding and Digestion Members of this phylum are filter feeders, herbivores or active carnivores All members have a one way gut with two openings Bivalves are filter feeders using the siphon to gather water to filter Gastropods tend to gather algae using their radula Cephalopods are carnivores that capture their prey using their arms and tentacles and then chew up the prey using a hard beak found between the arms

Excretion Have a complex excretion system that gathers waste in a nephridia (similar to our kidneys) This system recovers water and nutrients and expels a concentrated waste product

Circulation and Respiration Complex circulatory system that moves nutrients through the body Most members have a three chambered heart Marine mollusks have gills located in the mantle cavity

Reproduction Most members have distinct male and female sexual members Some have the ability to change sexes between male and female This helps keep the population high by providing the right ratio of male to female

Class Gastropoda Include snails, slugs, nudibranches and abalones Range in size from microscopic to 1 meter Most have a single shell but some have lost this shell completely like the slug and nudibranch Most have tentacles on top of their head that contain simple eyes Often a source of food for humans Most are herbivores

Class Bivalves Examples are clams, mussels and oysters The body is laterally compressed with two shells that are hinged at the bottom Gills are used not only for respiration but also to filter debris out of the water for feeding Strong muscles are used to open and close the shell Have sense organs on the edge of the mantle that respond to light and touch

Class Bivalves cont. Some have siphons which are used to bring oxygen to the bivalve that is buried in the sand; allows buried organisms to filter feed They have byssal threads which they use to attach themselves to hard surfaces Pearls are produced by oysters or clams – the pearl is basically the same material that the shell is made of: It forms around a piece of sand, debris or irritation that has gotten into the body cavity and is irritating the clam

Class Cephalopods Characterized as strong predators that specialized in movement Group includes octopus, squids, cuttlefish and nautilius. Most are active swimmers that have a vestigial shell present, but reduced in size and not used by the animal Movement is achieved by bringing water into the funnel and pushed out the siphon The funnel is a muscular part of the foot found under the head The siphon is another tube that is flexible and moveable to help steer the squid Foot is modified into tentacle with sucker discs to capture prey

Class Cephalopoda Octopuses have eight arms and range in size between 2 inches and 30 feet Squid have eight arms and two long tentacles and range in size between a few inches to more than 65 feet All members of this class squirt ink if disturbed – this acts as a smoke screen to hide them from predators the members of this class have a well defined brain and are capable of complex behaviors as seen in the movie “incredible suckers”