Phylum Mollusca � Protostomes
� Lophotrochozoan group
� Eucoelomates (coelomates)
Tridacna squamosa
Tridacna gigas
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
� Heart (2 chambers)
� Open system in most groups
� Closed in cephalopods
� Coelom restricted to pericardium in most cases
Octopus briareus
Phylum Mollusca
� Advanced nervous system � Brain
� Sensory organs � Eyes (simple and camera)
� Sensory papillae
� Excretory system � Kidney-like nephridia
� Reproduction � Monoecious and dioecious
� External development
� External & internal fertilization
Mollusc Phylogeny
� ~50-80K extant
species
� ~40K extinct species
� Fossil records
from precambrian period of
proterozoic eon (>570my BP)
Mollusc Taxonomy
� Major classes
�Polyplacophora
�Chitons
Chiton tuberculatus lives in the rocky intertidal zones
eat algae with its radula
8 shell plates
Mollusc Taxonomy
� Major classes
� Polyplacophora
�Gastropoda
�Subclasses:
�Prosobranchia
� Shelled marine
gastropods
Atlantic triton’s trumpet (Charonia variegata)
Tiger cowrie (Cypraea tigris)
Mollusc Taxonomy
� Major classes
� Polyplacophora
�Gastropoda
�Subclasses: � Prosobranchia
�Opisthobranchia
� Sea slugs (marine) zebra sea goddess (Hypselodoris zebra)
Spotted sea hare (Aplysia dactylomela
Phidiana hiltoni
Mollusc Taxonomy
� Major classes
� Polyplacophora
�Gastropoda
�Subclasses: � Prosobranchia
� Opisthobranchia
�Pulmonata
� Terrestrial snails/slugs
� Freshwater
snails
Helminthoglypta walkeriana
Giant banana slug (Ariolimax columbians)
Mollusc Taxonomy
� Major classes
� Polyplacophora
� Gastropoda
�Bivalvia � Clams, oysters,
mussels, scallops
Bay scallop (Aequipecten irradians)
Edible mussels (Mytilus edulis)
Ostrea edulis
Mollusc Taxonomy
� Major classes � Polyplacophora
� Gastropoda
� Bivalvia
� Cephalopoda
� Octopus, squid, nautilus
Giant cuttlefish (Sepia latimanus)
Nautilus sp
Octopus sp
Mollusc Taxonomy
� Major classes
� Polyplacophora
� Gastropoda
� Bivalvia
� Cephalopoda
� Minor classes
� Monoplacophora
� Solenogastres
� Caudofoveata
Mollusc Reproduction & Development
� 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
Terrestrial Gastropods - Pulmonata
� The mantle cavity serves
as a “lung”
� Glandular epidermis
� Secrete mucus (slime)
upon which gastropod
glides
Terrestrial Gastropod - Pulmonata
� Slugs lack
shells
� Mantle thickened
� Pneumostome
� Air intake into mantle cavity
Pneumostome
Glochidia – Unique Larval Stage of Freshwater Bivalves
� 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
Phylum Mollusca, Class Cephalopoda
� 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