Phylum Mollusca• chitons, clams, snails, slugs, octopi,

cuttlefish, squid, & nautili

• second largest phylum (50,000+ species)

• well known fossil record

• marine, fresh water, and terrestrial

General Characteristics

• mostly bilateral symmetry• unsegmented• eucoelomates; protostomes• great size variation• great diversity & adaptive radiation

Body Plan• cephalization

• muscular foot; modified as tentacles in cephalopods

• mantle- surrounding the viscera; shell secretion & jet propulsion

• calcareous shell: protection & support; nacreous layer & periostracum

• radula: feeding in herbivorous species

• gills: respiration & filter feeding

Radula

Snail Radula

Ctenidia- Gr. “comb”

Physiology/Development• open circulatory system except

cephalopods; hemocoel

• excretion: metanephridia

• nervous system- ganglion

• external & internal fertilization

Class Polyplacophora: “chitons”

• 800 species• marine• inhabit rocky intertidal zone• dorsoventrally flattened• overlapping dorsal shell plates• herbivores w/ radula

Polyplacophora – “chitons”

Chiton Anatomy

Class Aplacophora

Aplacophora- Diagnostic Features

• small, vermiform

• deep marine

• no shell; calcareous spines

• many burrowing or on cnidarians

Monoplacophora

Monoplacophora- continued

• all deep marine

• single, unhinged, cap-shaped shell

• 3-6 ctenidia

• ancestor possibly gave rise to other molluscs

Class Gastropoda• largest taxonomic class

• 30,000 extant species

• snails, nudibranchs, sea hares, and slugs

• marine, freshwater, and terrestrial

• shell often asymmetrical spiral

columella

Cone Shells

C. Gastropoda; S.C. Pulmonata

• A. heart• B. penis• D. dart sac• E. sperm duct• F. oviduct• H. digestive gland• I. Stomach• J. crop• K. esophagus• L. buccal bulb

nudibranchs/sea hares

Veliger Larvae

Class Bivalvia• clams, scallops,

oysters, and mussels

• filter feeding

• mantle secretes a shell of CaCO3

• periostracum, prismatic, & nacreous layers

Clam Anatomy• muscular foot• intestine• gonad• hemocoel• mantle• gills• excurrent/incurrent

apertures

Muscular Foot

clam glochidia

Class Scaphopoda• “Tusk Shells”

• openings at both ends

• captacula- adhesive feeding tentacles

Class Cephalopoda • octopods, squid, cuttlefish, & Nautilus

• ~ 600 species; entirely marine

• highly motile- jet propulsion

• highly developed nervous system and sensory

• shell reduced or entirely absent in octopods; 5-6 Nautilus possess shells

Reproduction/Development

• dioecious

• internal fertilization; spermatophore

• no larval phase

• female often broods the eggs before dying

chromatophores

Nautilus

Giant Squid (Architeuthis)