Mollusca Soft bodied animals that usually have an

Mollusca • Soft- bodied animals that usually have an internal or external shell • Very diverse group: snails, slugs, clams, squids, and octopus • Share similar developmental stage.

Body Plan 4 parts: foot, mantle, shell, visceral mass • Foot- flat for crawling, spade shaped for burrowing, tentacles for prey capture • Mantle- thin layer covers most of mollusk’s body, contains glands that secrete shell • Shell- calcium carbonate: some mollusks have lost their shell (slugs) • Visceral mass- internal organs.

Feeding • wide range: filter feeders, herbivores, carnivores, parasites • Snails/ Slugs- radula flexible, tongue like structure for eating/scraping • Clams/Oysters/Scallops- siphon (tube-like structure for water) • Squid/ octopus - beak

Respiration • A. land- moist cavity in mantle, lined with blood vessels to exchange gases • B. Aquatic- gills.

Circulation • open circulatory system- use of sinuses (open sacs for blood return): good for slow moving creatures • closed circulatory system- blood always contained in tubes. (only cephalopods)

Excretion • Nephridia- specialized cells for removing liquid waste, known as ammonia. • Aquatic expel waste out siphon

Response • greatly varied nervous system – simple- ganglia, eyespots, chemical receptors – complex- brains, nervous system, eyes.

Movement • many different ways – snail- mucus on foot with rippling motion – octopus- jet propulsion.

Reproduction usually sexually: – external fertilization – Internal fertilization – hermaphrodites.

3 groups • Gastropods • Bivalves • Cephelapods

Gastropods (stomach foot) • shell-less or single shelled mollusks that move by using a muscular foot located on the ventral side • snails, slugs, sea hares, limpets, and nudibranches.

Sea Hare

Bivalves • 2 shells that are held together by one or two powerful muscles • ex: clams, muscles, oysters, scallops.

Cephalopods (head foot) • typically soft-bodied in which the head is attached to a single foot: the foot is divided into tentacles or arms • squid, octopi, cuttlefish, nautiluses.

Nautilus