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The functional morphology of the radular teeth and feeding tracks of the common Japanese chi ton Liolophura japonica are investigated. About 90 transverse rows of radular teeth are tangentially placed... on a long but narrow radular ribbon. Each transverse row consists of 17 teeth arranged in bilateral symmetry: a central tooth, two central lateral teeth, two major lateral teeth, and two major uncinuses that are spoon-like. Two inner and two outer small lateral teeth are block-like. The major uncinus and the small lateral teeth support the major lateral tooth. Two inner, two middle, and two outer marginal teeth are plate-like and form a side wall of the cylindrical radular ribbon, the anterior part of which serves to lead food down the esophagus. The major lateral teeth in the 1st to 8th rows have numerous scratches on the cusp and lack the major projection. VTR observations of radular movement show that L. japonica has a weaker and a stronger method of grazing. The former is not strong enough to produce feeding tracks on an acrylic or metacrylic sheet in a tank. Analysis of feeding tracks on artificial substrates provides idealized sets of impressions of feeding strokes. A single feeding stroke produces 3 to 5 bilaterally symmetrical chevron-shaped feeding tracks. This evidence suggests that only the cusps of the anterior 4th through 8th major lateral teeth are usually used for feeding. For these feeding tracks the new ichnogenus Chitonichnus with its type ichnospecies C. liolophurus (new ichnospecies) is proposed. The result of X-ray diffraction methods shows that the major lateral of L. japonica has a magnetite cusp. The magnetite cusp in chitons may primarily be an adaptation for grazing hard substances.続きを見る
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