GAMETOGENESIS DURING THE ANNUAL REPRODUCTIVE CYCLE IN A CIDAROID SEA URCHIN (STYLOCIDARIS AFFINIS)

¹ Department of Marine Biology, Scripps Institution of Oceanography, University of California at San Diego, La Jolla, California 92037, and Stazione Zoologica di Napoli, Naples, Italy

1. Periodic sampling of a Neapolitan population of the cidaroid sea urchin Stylocidaris affinis, revealed an annual reproductive cycle.

2. In female urchins, primary oocyte growth begins only in September and continues for almost a year until maximum size is attained the following August.

3. In the oocytes of this species, conspicuous components of the yolk granules are protein and neutral mucopolysaccharide. Acid mucopolysaccharides, probably destined to be cortical components of the ripe egg, are synthesized only as the primary oocytes are nearing their maximum size.

4. After reaching their maximum size in August, the primary oocytes undergo maturation divisions (probably en masse) to become ripe eggs. The ripe eggs are apparently shed soon after being produced in August or September.

5. In male urchins, spermatogonia give rise to spermatocytes, which accumulate in an ever-thickening layer in the testes during the winter, spring and summer. The spermatocytes seem blocked from differentiating into more advanced germinal cell types until late summer, when they abruptly differentiate into spermatids and subsequently spermatozoa. The spermatozoa are apparently shed in late August or early September.

6. The lack of an extended period of egg accumulation in the female urchins as well as the presence of an extended period of spermatocyte accumulation in the male urchins, sets gametogenesis in this cidaroid (subclass: Perischoechinoidea) apart from gametogenesis in other echinoids that have been studied (subclass: Euechinoidea).

7. The possible control of the annual reproductive cycle by exogenous environmental factors is discussed.