Info

Class

External shell Head

Radula

Locomotion

Gastropoda

one (most species) yes

yes

crawling (most)

Bivalvia

two no

no

sessile (most)

Cephalopoda

none (most species) yes

yes

rapid swimming

Terrestrial snails use the radula to cut through the leaves of garden plants, while aquatic snails use it to scrape up algae or to drill holes in the shells of other mollusks. The cone shell has a harpoon-shaped radula with which it captures fish and injects venom.

Most biologists use structural differences to divide mollusks into seven classes. Three of these classes are discussed below: class Gastropoda (gas-TRAHP-uh-duh), class Bivalvia (bie-VALV-ee-uh), and class Cephalopoda (SEF-uh-LAHP-uh-duh). Table 35-1 summarizes the major features of these three classes.

Word Roots and Origins gastropod from the Greek gaster, meaning "stomach," and pous, meaning "foot"

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