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Polyplacophorans, commonly called chitons, are marine mollusks identified by their flattened, oval bodies with eight overlapping dorsal plates. These plates act as armor to protect them from harsh waves and predators. Chitons clingy tightly to rocks within intertidal and subtidal zones, using a strong muscular foot to stay in place. Their foot and mouth are both ventral to the body, allowing polyplacophorans to feed as they move across surfaces. Many graze on seaweeds or other small invertebrates they find on rocky shores making them important members of bethic communities.
Defining Characteristics
Defining Characteristics
Flattened body plan and oval shape
Bilateral symmetry
Triploblastic body plan: endoderm, mesoderm, ectoderm
Eight overlapping dorsal plates
Form a protective shell
Distinctive dorsal stripes
Ventral muscular foot
Ventral mouth with radula
Head reduced with no true cephalization
Nervous system with paired nerve cords and small ganglia
Complete digestive tract: separate openings for mouth and anus that allows for maximized digestive efficiency
Open circulatory system
Reproductive adaptations
Reproductive adaptations
Sexes mostly separate (dioecious), few species are hermaphroditic
Fertilization typically external with both eggs and sperm released into the water
Egg stage: small, yolk filled structures that float freely through the water
Trochophore larva: Tiny, ciliated larval stage that feeds on plankton
Metamorphosis: The larva settles into substrate and transforms into a juvenile chiton with eight plates and a foot
Some species have direct development skip this larval stage
Adult Stage: Reproductive system fully developed with the capability of mating
Where are they found?
Where are they found?
Only reside in marine environments
Rocky intertidal and subtidal zones
Under stones
Packed within small crevices
Tropical to polar regions
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