ABSTRACT
The chromosome numbers of sea urchins reported until now are 2n=42, 44 and 46. The sea urchins belonging to the order Echinoidea have 2n=42, those belonging to Arbacioida, Diadematoida or Cidaroida show 2n=44, and those belonging to Clypeasteroida are 2n=46. Further karyotypic comparison seems necessary to discuss echinoid taxonomy cytogenetically, since the chromosome numbers are the same among the species belonging to the same order in Echinoida, Arbacioida and Clypeasteroida. For karyotype analysis, the sea urchins of 10 species consisting of above three orders were collected in Japanese water. Chromosome preparations were made using embryos at the morula or the early blastula stage by the air-drying method after colchicine and then hypotonic treatments. The karyotypes of 10 species varied with the difference of the genus and the different species belonging to the same genus showed a similar karyotype. The difference in karyotypes corresponded to the classification based on morphological standpoints.
