Chromosome numbers in 8 Japanese species of sea urchins

Chromosome numbers were examined in 8 Japanese species of sea urchins. In Regularia, Glyptocidaris crenularis belonging to the order Arbacioida had chromosome number of 2n = 44 and Temnopleurus hardwickii, Pseudocentrotus depressus, Strongylocentrotus nudus, Hemicentrotus pulcherrimus and Anthocidaris crassispina belonging to the order Echinoida all showed chromosome numbers of 2n = 42. On the other hand, in Irregularia, both Scaphechinus mirabilisand Astriclypeus manni belonging to the order Clypeasteroida had chromosome number of 2n = 46. The chromosome numbers were found to be the same in the species belonging to the same order but differ chromosome numbers were found to be the same in the species belonging to the same order but differ among three different orders.