Embrionary and larval development of the marine clam Tivela mactroides (Bivalvia: Veneridae) in Zulia State, Venezuela.

The marine clam, Tivela mactroides, from Caño Sagua beach, Venezuela, was spawned and reared under laboratory conditions to monitor its early development. Spawning was spontaneous but in some cases it had to be induced by the additon of eggs and sperm. After fertilization, the embryonic development occurred at 5 hr approximately. Trochophore larvae were observed between eight and ten hours later. Straight-hinged veliger stage appeared 15 hr after fertilization. Transition from veliger stage to the umbo stage occurred about eight days after fertilization. Pediveliger stage was observed 22 days after fertilization. Metamorphosis of T. mactroides was not successful under our laboratory conditions; probably the bacterial contamination and subsequent mortalities were important factors constraining the final phase of the larval cycle. However, in a few cases young individuals were observed. We suspect that this was due to unfavorable conditions (e.g.: bacterial contamination, unsuitable food availability, etc.) and the broad variation in developmental times, suggesting that these stages might be particularly sensitive to environmental changes. These results may not necessarily reflect what happens under natural conditions.