Morphological variability of recent species of the order Cassiduloida (Echinodermata: Echinoidea) of Mexico

ntroduction: In Mexico, there are two recorded living species of Cassiduloida: Cassidulus caribaearum and Rhyncholampas pacifica. Most the taxonomic studies on cassiduloids have used external morphology, pedicellariae morphometric characters; however, intraspecific variation quantitative qualitative characters has been poorly evaluated. Objective: To compare basic morphology R. pacifica C. caribaearum. Methods: We examined a total 2 158 specimens caribaearum, selecting 50 to evaluate shape size with linear regression Principal Component analysis. selected an additional 62 per identify significant character correlations morphological groups within species. Results: There is direct relationship between Test length width. height/Test width, Total (oral view)/Distance from ambitus peristome apex, main ratios distinguish both more dorsoventrally compressed round base; versus tall triangular one. four for Conclusions: These can be distinguished reliable characters, in which suggests that adapted burrowing deeper into certain types substratum.