New outlook on the system of chitons (Mollusca: Polyplacophora)

Abstract

In order to build а natural classification of the chitons, а new approach is proposed that uses not only the shells, as usual, but also other suitable features including aesthetes, girdle, radula, gills, glands, egg hull projections, spermatozoids etc. Several previous classifications are discussed. А brief review of the evolution of the Polyplacophora is given and а new classification of the chitons is proposed. The roles of the articulamentum and the reductions in the tegmentum in chitons are discussed. The evolutionary line of the reduction of slits is shown for the superfarnily Cryptoplacoidea. Specifically, the genera Heтiarthruт, Weedingia and Choriplax, which have unslitted valves, have Ьееп removed from the order Lepidopleurida and reassigned to the order Chitonida within the Cryptoplacoidea. Affinities of these and other genera within the Cryptoplacoidea are discussed.