1. Members of the aplacophoran family Chaetodermatidae (genera Falcidens and Chaetoderma) have a radula consisting of a single cone-shaped structure associated with a pair of teeth. In the genus Falcidens there also occurs a plate with two pairs of apophyses that wrap around the paired teeth. 2. One species of each genus is known to feed on foraminifera. 3. The buccal mass bears many similarities to the gastropod buccal mass: it lies in a buccal cavity; it is covered distally by a membrane connected to the radula, apparently the subradular membrane; it contains a pair of bolsters, from which run muscles to the radula and subradular membrane; and it has a blood sinus surrounding a sac of epithelial cells which secrete the cone-shaped radula. This sac appears to be homologous to the radula gland of other mollusks. It lies above and between the bolsters, and at its ventral, blind end are four large cells, the odontoblasts. 4. The cone-shaped median structure appears to be a fused, permanent, continuously secreted radula. The structures seen with scanning electron microscopy, the increase in size with size of animal, and the indication of tanning by the radula gland support this view.
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