Ontogenetic radular variation in species of Tambja Burn, 1962 (Gastropoda, Opisthobranchia, Polyceratidae) from the eastern Atlantic Ocean and the Mediterranean Sea

Résumé

Of the 10 species in the genus Tambja (Polyceratidae) described in the biogeographical Atlantic-Mediterranean subregion, 6 species were chosen for the present study because of their relative abundance in the eastern Atlantic and Mediterranean area. Data are given on the variations in the number of radular tooth rows and their morphology for specimens at different developmental stages from juveniles to adults. Juvenile specimens smaller than 10 mm show a variable number of tooth rows which is always above 20. In juvenile specimens larger than 10 mm in length or the juvenile pre-adult and adult stages, the number of tooth rows is invariably lower than 20, but a positive linear relationship between body length and the number of tooth rows is still shown. The significance of this phenomenon is not known at this time, although different hypotheses have been suggested.