A method of chromosome observation and karyotype in Pseudocentrotus depressus

Chromosomes of echinoid species have been stud ied by several researchers by using sectioning or squash method,1-3) but karyotypic details are not clearly known. Saotome4) established an air-drying method using Ca-Mg-free sea water and 1mm 3amino-1, 2, 4-triazole for eight species of Japanese sea urchins. According to her report, the chromosome numbers in Japanese sea urchins were found to have three orders, i.e., Arbacioida (2n=44), Echinoida (2n =42) and Clypeasteroida (2n=46). We obtained clear metaphase chromosome plates from blastema in our study by applying a flame drying method (Fig. 1), which is much simpler than that of Saotome.4) This report presents the new flame-drying method and karyotype of a common sea urchin Pseudocentrotus depressus.