Phylum Mollusca

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 Phylogeny � Mantle secreting

shell

� Muscular foot

� Chambered heart

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

Generalized Mollusc Anatomy

Gastropod Feeding Apparatus

Respiration: Gills

Shell Structure & Formation

A Pearl Among the Swine

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

Trochophore Larva

Gastropod Veliger Larva

Velia

Mouth

Shell

Zygote

Trochophore

Veliger

Spat

Juvenile

Adult

Adult Abalone

Class Polyplacophora - chitons

Polyplacophoran Anatomy

Class Gastropoda The Shell Game

Class Gastropoda - Torsion

Gastropod Shell Coiling

Gastropod Gill/Mantle Cavity Evolution

Generalized Gastropod Anatomy

Marine Gastropods

Cowries

Marine Gastropods

Sea Hare – Aplysia sp

Marine Gastropods - Nudibranch

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

Phylum Mollusca, Class Bilvalia

� Two shells

� Incurrent & excurrent siphons

� No cephalization

Generalized Bivalve Anatomy

Generalized Bivalve Anatomy (XS)

Bivalve Anatomy (Sagittal)

Bivalves are Typically Filter Feeders

Bivalve Life Cycle

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

Cephalopod Anatomy

Squid are the largest Cephalopods

Nautilus Anatomy

Cephalopod Eye

Mating

Direct Development in Cephalopods

Color & Morphology Changes for Camouflage