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
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