2016 年 40 巻 p. 22-29
Two forms of test are known in a fibulariid sea urchin, Fibulariella acuta (Yoshiwara, 1898). One is a "rice grain-shaped" in which both the anterior and the posterior tips are pointed. Another is an "egg-shaped" in which the anterior tip is pointed but the posterior is broad. This species was originally described as "egg-shaped;" nevertheless, the post described drawing of the syntype by the same author showed its "rice grain-shaped." Although many taxonomic examinations have been made to understand the meaning of difference between the two forms, the meaning has not been clarified until today. We here compared the external morphologies of the test and pedicellariae between the two forms based on 59 specimens from Kumamoto Prefecture, Japan. In addition to the external outline of the tests, morphology of pedicellariae was clearly different between the rice grain-shaped and egg-shaped specimens as follows: the former had three types of pedicellariae (globiferous, bidentate, and biphyllous), whereas the latter had only two types (globiferous and bidentate). These morphological differences suggest that the two forms of F. acuta should be revised as two different species.