ANPMSS SubjectZoology ChapterPhylum Mollusca Phylum Mollusca Phylum Mollusca

ANPMSS Subject-Zoology Chapter-Phylum Mollusca

Phylum Mollusca

Phylum Mollusca �Protostomes �Lophotrochozoan �Eucoelomates group (coelomates) Tridacna gigas Tridacna squamosa

Phylum Mollusca �Soft Bodied �Shelled ◦ Some without �Cephalization ◦ Sensory organs ◦ Mouths �Body Divisions ◦ Visceral Mass ◦ Head-Foot ◦ Mantle Tonicella lineata

Phylum Mollusca �Complete digestive tract �Digestive glands �Specialized feeding structures �Circulatory system Octopus briareus ◦ Heart (2 chambers) ◦ Open system in most groups ◦ Closed in cephalopods �Coelom cases restricted to pericardium in most

�Advanced system nervous ◦ Brain ◦ Sensory organs �Eyes (simple and camera) �Sensory papillae �Excretory system ◦ Kidney-like nephridia �Reproduction ◦ Monoecious and dioecious ◦ External development ◦ External & internal fertilization Phylum Mollusca

Mollusc Phylogeny �~50 -80 K extant species �~40 K extinct species �Fossil records from precambrian period of proterozoic eon (>570 my BP)

Mollusc Phylogeny �Mantle secreting shell �Muscular foot �Chambered heart

Chiton tuberculatus lives �Major classes in the rocky intertidal ◦ Polyplacophora zones eat algae with its radula � Chitons 8 shell plates Mollusc Taxonomy

Atlantic triton’s trumpet (Charonia variegata) �Major classes ◦ Polyplacophora ◦ Gastropoda � Subclasses: � Prosobranchi a ◦ Shelled marine gastropods Mollusc Taxonomy Tiger cowrie (Cypraea tigris)

Spotted sea hare (Aplysia dactylomela �Major classes ◦ Polyplacophora ◦ Gastropoda � Subclasses: �Prosobranchia � Opisthobranc hia Phidiana hiltoni ◦ Sea slugs (marine) Mollusc Taxonomy zebra sea goddess (Hypselodoris zebra)

Helminthoglypta walkeriana �Major classes ◦ Polyplacophora ◦ Gastropoda � Subclasses: �Prosobranchia �Opisthobranchia � Pulmonata ◦ Terrestrial snails/slugs ◦ Freshwater snails Mollusc Taxonomy Giant banana slug (Ariolimax columbians)

�Major classes ◦ Polyplacophora ◦ Gastropoda Bay scallop (Aequipecten irradians) ◦ Bivalvia �Clams, oysters, mussels, scallops Edible mussels (Mytilus edulis) Ostrea edulis Mollusc Taxonomy

Giant cuttlefish (Sepia latimanus) �Major classes ◦ Polyplacophora ◦ Gastropoda ◦ Bivalvia ◦ Cephalopoda Octopus sp �Octopus, squid, nautilus Nautilus sp Mollusc Taxonomy

�Major classes ◦ Polyplacophora ◦ Gastropoda ◦ Bivalvia ◦ Cephalopoda �Minor classes ◦ Monoplacophora ◦ Solenogastres ◦ Caudofoveata Mollusc Taxonomy

Generalized Mollusc Anatomy

Gastropod Feeding Apparatus

Respiration: Gills

Shell Structure & Formation

A Pearl Among the Swine

�Indirect development ◦ Larval stages ◦ Trochophore larva �Free swimming, ciliated, shell formation begins ◦ Veliger larva �Free swimming, ciliated velium forms, �Shell/body torsion occurs ◦ Spat �Metamorphic form between veliger and juvenile �Shell elaborates Mollusc Reproduction & Development

Trochophore Larva

Mouth Velia Shell Gastropod Veliger Larva

Veliger Zygote Trochophore Juvenile Spat Adult

Adult Abalone

Class Polyplacophora - chitons

Polyplacophoran Anatomy

The Shell Game Class Gastropoda

Class Gastropoda - Torsion

Gastropod Shell Coiling

Gill/Mantle Cavity Evolution

Generalized Gastropod Anatomy

Marine Gastropods Cowries

Sea Hare – Aplysia sp Marine Gastropods

Marine Gastropods Nudibranch

Terrestrial Gastropods - Pulmonata �The mantle cavity serves as a “lung” �Glandular epidermis ◦ Secrete mucus (slime) upon which gastropod glides

Pneumostome �Slugs lack shells �Mantle thickened Terrestrial Gastropod �Pneumostome Pulmonata ◦ Air intake into mantle cavity -

�Two shells �Incurrent & excurrent siphons �No cephalization Phylum Mollusca, Class Bilvalia

Generalized Bivalve Anatomy

Generalized Bivalve Anatomy (XS)

Bivalve Anatomy (Sagittal)

Bivalves are Typically Filter Feeders

Bivalve Life Cycle

�Internal fertilization �Early development in brood chamber (region of mantle cavity) �Release of glochidia veliger larvae �Glochidia attach to gills of fish and are distributed Glochidia – Unique Larval Stage of Freshwater Bivalves

�Closed circulatory system �Shell: lost in Octopus, extremely reduced and enclosed in mantle in squid, planar spiral in Nautilus �Cephalization ◦ eye ◦ Beak around mouth �Tentacles/arms Phylum Mollusca, Class Cephalopoda

Cephalopod Anatomy

Squid are the largest Cephalopods

Nautilus Anatomy

Cephalopod Eye

Mating

Direct Development in Cephalopods

Color & Morphology Changes for Camouflage