Phylum Mollusca “Soft Body”

Mollusca (Soft Body) 4 Major Classes Scaphopoda -- Tooth, tusk shell Bivalvia (pelecypoda) -- Clams, mussels, oysters Gastropoda -- Snails, conchs, welks Cephalopoda -- Squids, octopus, nautili

Common Characteristics Bilateral Symmetry - anterior head Mantle - Secretes calcium carbonate shell (CaCo3) Muscular Foot - Burrowing & crawling Digestion: complete - Mouth with radula (tongue with teeth) Glands - liver & salivary Circulatory - Generally open with dorsal heart and vessels

Common Characteristics cont. Respiration - Gills (ctenidia), mantle (epidermis) Excretory - Kidneys (nephridia) Nervous system - Several pair of ganglia (cerebral, pedal, visceral) form connective nerve system Reproduction - Sexes separate (dioecious) or together (monoecious). External sexual fertilization (oviparous)

Common Characteristics cont. Free living, mostly aquatic (marine), some terrestrial Economic importance - Food, jewelry (shells, pearls, etc), some negative impact...

Class Scaphopoda - “Tusk Shell” Marine, burrow with foot into mud or sand No head, lacks gills Mantle absorbs oxygen from water Ciliated, contractile tentacles surround mouth

Class Scaphopoda cont... No eyes or other distinct sensory organs Several pair of ganglia form a coordinated sensory system Uses captacula (tentacles extending from foot) to find food in sediment and carry it to the mouth Reproduction - separate sexes - external fertilization. Fertilized egg develops into larvae

Class Bivalvia - “Two shells” Clams, oysters, mussels, scallops - exoskeleton of two shells AKA “pelecypoda” (hatchet foot) Bilateral symmetry No head Filter feeders - no radula Gills serve two purposes Oxygen absorption Food filtration

Bivalvia cont... Muscular foot Scallops can “swim” Water flows through siphons Incurrent - ventral Excurrent - dorsal Flow created by cilia

Bivalvia cont... Muscular system Adductors - close valves Muscular foot operated by protractors & retractors Respiration Mantle; thin double gill Aquatic Some marine Bottom dwellers

Bivalvia cont... Umbo - oldest part of the shell Shell grows outward in concentric rings Simple nervous system - no brain Generally lack sensory organs Scallops have complex eyes Three chambered heart Reproduction Sexes generally separate External fertilization (oviparous)

Gastropoda (Belly foot) Largest, most diverse class: 40,000 living and 15,000 extinct species. Snails, slugs, conchs Generally bilateral symmetry

Gastropoda cont... Dorsal shell contains visceral mass Univalve (CaCo3); Apex is central point of shell & is oldest. Successive layers are called whorls, formed around a central axis called columella

Gastropoda cont. Anterior head Pair of tentacles, each with an “eye” Radula used in feeding Most important sensory organ are olfactory receptors, located at the tips of tentacles Movement with muscular foot

Gastropoda cont. Respiratory - Lungs in terrestrial species complete with network of blood vessels Well developed, coordinated nervous system Generally monoecious

Cephalopoda (head-foot) Squids, octopus, nautili Most developed mollusc Large anterior head with 2 well developed eyes Tentacles - suction cups located radially around mouth

Cephalopoda cont... Mouth - beak & radula Foot - modified into a funnel-like siphon Respiration Circulation Jet propulsion

Cephalopoda cont... Dioecious -- sexes separate Internal sexual fertilization Develop internal eggs, hatch into miniature which are able to feed & swim Shell lacking or reduced to internal structure In squid, “pen” is remnant of shell -- feather shape structure that supports mantle, serves as site for muscle attachment Nautilus has external CaCo3 shell

Cephalopoda cont... Nervous system -- Brain with coordinated ganglia Marine Ink Sac -- self-defense mechanism present in all cephalopods except Nautilus