GONADAL DEVELOPMENT DURING THE ANNUAL REPRODUCTIVE CYCLE OF COMANTHUS JAPONICA (ECHINODERMATA: CRINOIDEA)

¹ Division of Marine Biology, Scripps Institution of Oceanography, University of California at San Diego, La Jolla, California 92037, and Misaki Marine Biological Station of the University of Tokyo, Misaki, Kanagawa-ken, Japan

1. Periodic sampling of a Japanese population of an unstalked crinoid, Comanthus japonica, demonstrated an annual reproductive cycle delimited by spawning in October.

2. In both sexes, the first weeks after spawning were a time of phagocytosis of unspawned germinal cells by non-germinal cells of the inner layer of the gonad.

3. In November, gonial cells made their appearance in the inner layer of the gonad, which was unsexable for several weeks.

4. In females, during the latter part of November, oogonia began differentiating into oocytes and continued to do so until mid February; this resulted in an oocyte population in which the largest cells were three months older than the smallest cells.

5. During the winter, spring and summer, the oocyte population grew as a single generation until spawning in October; although there was some tendency for the smaller oocytes to catch up with the larger ones, oocyte diameters ranged from about 145 µ to 225 µ on the day of spawning. The instantaneous relative growth rates of all oocytes were high at first and then decreased during later growth.

6. In each ovary, at least two to three times as many oocytes were initially produced as were finally present just before spawning; a large female emitted about two million gametes on the day of spawning each year.

7. Prior to late September, oocyte morphology depended on oocyte size. The following changes occurred at the following oocyte diameters; yolk granule synthesis started at 12 µ; the diplotene chromosomes disappeared at 100 µ; and cortical granule synthesis started at 115 µ.

8. From late September to spawning in October, all the oocytes in an ovary began to differentiate almost simultaneously, irrespective of their size. During this short period, the nucleus and nucleolus swelled conspicuously, extracellular jelly appeared, and the oocyte surface became dented with hundreds of pits, each about 10 µ deep. Finally, several days before spawning, annulate lamellae appeared in the cytoplasm, and diakinesis chromosomes appeared in the nucleus.

9. In males, the spermatogonia divided mitotically throughout the winter, spring and early summer without differentiating into more advanced germinal cell types; during this period, the maximum mean cell cycle time was about 35 days. Subsequently, from mid summer through spawning in October, the spermatogonia differentiated, via spermatocytes and spermatids, into spermatozoa.