A COMPARATIVE STUDY ON GLOCHIDIAL MORPHOLOGY OF UNIONIDAE (BIVALVIA)──Ⅰ.Unio douglasiae, Cuneopsis pisciulus, Acuticosta chinensis and Acuticosta ovata

Glochidial morphology of four unionid species, Unio douglasiae (Gray),Cuneopsis pisciulus (Heude), Acuticosta chinensis (Lea) and A. ovata (Simpson), was studied tinder optical and scanning electron microscope (SEW). Specimens were all collected from Poyang Lake of Jiangxi Province.In adults of the four species, only outer demibranchs are used as marsupia, in which U. douglasiae and A. chinensis form conglutination whereas C. pisciulus and A. ovata have separate embryos. In comparison of the glochidia, significant differences were found among the species. A. chinensis differs from the others by having gourd-shaped shell and numerous delicate spines on the hooks. C. pisciulus has fine,concentric wrinkles on the ventral margin and obviously long hooks. A. ovata and U.douglasiae are similar to each other in shell shape, however, the former has pores on the shell-surface and the latter has only shallow pits. Sensory hairs of glochidia were observed to have three pairs in U. douglasiae and A. chinensis, and four pairs in C.pisciulus. No sensory hair was found in A. ovata, probably due to long preservation.