EMBRYONIC AND LARVAL DEVELOPMENT OF SPISULA-SOLIDISSIMA-SIMILIS (SAY,1822) (BIVALVIA, MACTRIDAE)

Larvae of the southern surf clam, Spisula solidissima similis (Say, 18 22), were reared in the laboratory at a salinity of 25 ppt and a tempe rature of 20-22 degrees C through the embryonic and early larval devel opment period. Unfertilized eggs averaged 58.5 +/- 0.32 (SE) mu m, wit h the size-frequency of eggs being normal. First polar body was observ ed 22 minutes after fertilization with 50% of eggs exhibiting polar bo dies after 26 minutes. Ciliated blastula and trochophore stages occurr ed at 6 hours and 16.8 hours, respectively. Straight-hinge veligers ap peared 39.2 hours after fertilization. Larvae grew to a mean size of 1 72 mu m in the pediveliger phase (range 119 to 212 mu m). Larvae were exhibiting active foot-probing by day 8 and continued to do so until d ay 13 when the cultures suffered heavy mortalities. Early life-history traits of Spisula solidissima similis larvae are compared to those fo r Spisula solidissima solidissima and Spisula sachalinensis.