Comparative research on karyotype in three species of Arcidae

By air-dry method, the karyotype from gill cell in three clams of Bivalvia Pterimorphia Arcidae,Tegillarca granosa, Scapharca subcrenata and S. broughtonii. Was studied. Their chromosome number(2n) and fundamental number (NF) are equal to each other. But their karyotype is different. In T. grunasa. it is 2n=38, 28m+10sm; In S. subcrenata 2n=38, 14m+22sm+2st. In S. broughtonii 2n=38, 12m+20sm+6st. T.granosa has no subtelocentric (st) chromosome. S. subcrenata has one pair and S. broughtonii has three paris of st. Middle centric (m) and submiddle centric chromosome are major type in karyotype of three species of Arcida; the lengths of chtotnosomes from the largest to the smallest changed gradually. The absolute length of the maximum chromosome in all three species do not exceed 5 μm and the minimum chromosome is about 2 μm. Inversion pericentric perhaps plays an important role in the evolution of chromosome. Hybridization among the three species of Arcidae is possible.