Analysis on a sample of Echinodiscus cf. auritus Leske, 1778 (Echinoidea Clypeasteroida)

In order to ascertain the extent of the natural intraspecific variability of living and fossil echinoids belonging to the family Astriclypeidae Stefanini, 1912, morphometric and structural aspects were examined in a number of specimens of extant Echinodiscus cf. auritus Leske, 1778, from Madagascar and Philippines. The data obtained will be compared, in a following work, with those of other echinoids belonging to the same family. The analysis of the results indicates, for the sample studied, a great variability in the length of the posterior ambulacral notches, in the petaloid length and in the position of the periproct respect to the posterior margin, while the study of the complete scheme of the plates has clarified the stability and constancy of some parts of this scheme and the variability of other. On the basis of these observations, it has been claimed that the variability of these measures is not so extensive as to affect or determine specific distinctions, if used without careful analysis of the plating pattern in particular in the interambulacrum 5 and in the ambulacra I and II. The results of these analyses, finally, suggests that these echinoids belong to a different genus, than Echinodiscus Leske, 1778.