Soft-bodied animals that usually have an internal or external shell. Includes snails, slugs, clams, squids, and octopi. True coelom Complex, interrelated organ systems Body Plan The body plan of most mollusks have 4 main parts: foot 2. mantle 3. shell 4.

visceral mass Foot: muscular; may be used for crawling, burrowing or tentacles for capturing prey Mantle: thin tissue layer that covers the body (cloak) Shell: made by glands in the mantle that secrete calcium carbonateVisceral mass: internal organs Feeding Many (snails, slugs) use radula: flexible, tongue-shaped structure with hundreds of tiny teeth to scrape food, or drill into other animals Octopus: sharp jaws to eat prey Clams, oysters, scallops: filter feeders; use siphon tube-like structure through which water flows Respiration Aquatic mollusks use gills Land mollusks use mantle cavity; large surface area lined with blood vessels. It is kept moist and oxygen diffuses across.Circulation Open circulatory system:(snails, clams) blood is pumped through vessels by a simple heart and orks its way into the sinuses; blood then passes to the gills, where oxygen and carbon dioxide are exchanged. Closed circulatory system: (octopi, squid) capable of transporting blood faster Open vs.

Closed Response Clams (bivalves): simple nervous system, small ganglia, nerve cords and simple sense organs (eyespots, chemical receptors) Octopi: active predators; most highly developed nervous system of all invertebrates; welldeveloped brains; capable of complex behaviour, such as opening jars, responding to rewards.Reproduction Variety of methods; snails and bivalves reproduce sexually by external fertilization External fertilization: large number of eggs are released into the water, then fertilized by sperm; develop into free-swimming larvae. Tentacled mollusks: internal fertilization Some are hermaphrodites Groups Of Mollusks There are 3 groups of mollusks, they are: o Gastropods: shell-less or one shell, ventral foot. o Bi-valves: Two shells o Cephalopods: Head attached to foot.