REPRODUCTION IN TWO SYMPATRIC SPECIES OF MACOMA (BIVALVIA)

¹ Pacific Marine Station, University of the Pacific, Dillon Beach, California 94929

1. Spawning probably took two to three weeks for M. secta individuals and one to two days for M. nasuta individuals. Gonads of inactive M. secta are entirely disrupted and hardly recognizable, while gonads of M. nasuta remain organized and are filled with vacuolated follicle cells. Phagocytosis is pronounced only in spent males of M. secta.

2. M. nasuta females are characterized by noncellular spherical inclusions in follicle cells which are probably nutritive in function. They are numerous and large in size in the inactive stage and decrease in numbers and size as gametogenesis progresses.

3. The M. Secta population was rather synchronous in its progression through the gametogenic stages and spawned in August. Individuals of the M. nasuta population were rather asynchronous in passing through the gonadal cycle; the population spawned in May and from September through November.

4. The null hypotheses of 1:1 sex ratios were accepted for both species. No hermaphrodites were found nor any evidence for sex reversal in either species.