CLAMS,SQUIDS, OCTOPUSES, SNAILS, SLUGS, ETC. PHYLUM MOLLUSCA CLAMS,SQUIDS, OCTOPUSES, SNAILS, SLUGS, ETC.

General Characteristics More than 100,000 species “soft bodied” Bilaterally symetrical Trochophore larva 3 main body parts Mantle: thin membrane that surrounds the visceral mass, and secretes shell Visceral mass: digestion, excretion, and reproductive organs Head-foot: sense organs, mouth, and is used for locomotion

5 Major Classes of Mollusks Class Amphineura (Polyplacophora) – Chitons 8 calcareous plates on their dorsal surface Feed by grazing on algae along rocky intertidal zones Class Scaphopoda – Tusk Shells Elongated shell open at both ends that resemble elephant tusks Live in sandy or muddy bottoms Feed by extending tentacles into surrounding sediment or water

Class Gastropoda – Snails, slugs, nudibranchs, limpets, etc Class Gastropoda – Snails, slugs, nudibranchs, limpets, etc. (90,000+ species) Single shelled or no shell Means “stomach (or belly) foot” Body undergoes torsion - 180º rotation of internal organs, so that the anus ends up behind the head and waste products can exit the shell Radula for feeding Two types: one for scraping found in herbivores and one that is piercing found in carnivores Many have an opercula – trap door that closes off the shell for protection made of chitin

Class Bivalvia (Pelecypoda) – clams, mussels, oysters, scallops, etc. Two shells that they can close tightly for protection Filter feeders that brings in water and food using a siphon Some are burrowers, others attach themselves to rocks (most are sedentary) Some can manufacture pearls by secreting nacre to coat irritating particles

Class Cephalopoda – squids, octopuses, cuttlefish, and nautilus “head foot” because the feet (tentacles) are attached to the head Shell is either reduced (internal pen) or absent in all except for the nautilus Fast moving predators that use “jet” propulsion by expelling water through a siphon Mouth with a beak for feeding on fish Major types: Squid: 8 short arms and 2 long feeding tentacles Octopus: 8 arms Cuttle fish: 10 arms Nautilus: only one with external shell