Practice question

Radula, chitinous toothed ribbon supported by odontophore cartilage and protracted by buccal muscles for rasping food, occurs in most molluscan classes including Gastropoda snails, Cephalopoda squids with beak and radula, Polyplacophora chitons with massive radula for algal grazing, but is absent in Bivalvia where head is reduced, buccal apparatus lost and feeding adapted to ctenidial filter feeding via inhalant siphon trapping particles on gill mucus. Absence correlates with sedentary infaunal lifestyle, loss of cephalization and evolutionary shift to suspension feeding, making radula absence diagnostic criterion separating bivalves from other molluscs.