Phylum Mollusca1

Phylum Mollusca

Polyplacophora

Gastropoda

Bivalvia

Scaphopoda

Cephalopoda

Phylum Mollusca2

Molluscs

Have adapted to a wide variety of habitats

– Terrestrial, marine, benthic, and accomplished swimmers.

Phylum Mollusca3

The Molluscan Body Plan

The body plan is similar and distinct from all other phyla

The Mollusca body plan includes:– A large muscular foot– A radula– Mantle and mantle cavity– Usually a small head– Soft unsegmented body– A hard non-living calcareous shell

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The Foot

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The Radula

Radula

Some molluscs have a rod of digestive enzymes (crystalline style) in the stomach

Phylum Mollusca6

The Mantle

The mantle is the body wall that enclose the body cavity

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The Mantle Cavity

Houses the viscera and comb-like molluscan gills– Ctenidia are respiratory in function and can collect food

particles

Mantle cavity also is the site for reproductive, excretory, and digestive systems

Phylum Mollusca8

Taxonomic Summary

Phylum Mollusca– Class Polyplacophora– Class Gastropoda

Subclass Prosobranchia Subclass Opisthobranchia

– Class Bivalvia– Class Scaphopoda – Class Cephalopoda

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Class Polyplacophora

Defining characteristics– Shell forms as a series

of 7 to 8 separate plates Chitons

Phylum Mollusca10

Chiton Lifestyles

Found close to shore mainly in the intertidal where they live on hard substrates

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Chiton Anatomy

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Ingestion and Digestion

Radula is used to scrape algae from the rocks

Mouth is anterior and anus is posterior; linear digestive tract

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Reproduction

Reproduction– Sexes are separate with fertilization

occurring in the water column– Trochophore larvae

Free swimming which settles and metamorphoses into an adult

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Local Representative

Eastern Beaded Chiton (Chaetopleura apiculata)

– Occurs subtidally on old shells