Intraspecific and ontogenetic radular variation in opisthobranch systematics (Mollusca: Gastropoda). Systematic Zoology

often have been erected on numerical differences of the radular teeth. Regression analyses of radular counts of Discodoris evelinae (comprising also the synonymized species, D. hedgpethi) indicate intraspecific variation is ontogenetic. Predictions are given regarding the occurrence of this phenomenon among opisthobranchs, and suggestions are made for the use of radular characteristics in opisthobranch systematics. [Mollusca; Gastropoda; Discodoris; radula.] Many older taxonomic groups have turned out to be little more than size cate-gories (Ghiselin, 1971). In particular, spe-cies of opisthobranch mollusks have often been differentiated based on size differ-ences of the radulae or other parts of the anatomy, only later to be synonymized be-cause researchers collect intermediate forms. Certain opisthobranch species have a wide range of radular variation in the number of rows of teeth, and the number of teeth per half-row. However, except for the anaspidean Phyllaplysia taylori Dall, 1900 (see Beeman, 1963) and phanero-branch nudibranchs of the genus Trioph