Reproductive biology of the feather star Florometra serratissima: gonadal structure, breeding pattern, and periodicity of ovulation

The reproductive biology of a population of the feather star Florometra serratissima (A. H. Clark) was studied at Barkley Sound, British Columbia, Canada. Most individuals in the population are gonochoric, although hermaphrodites are present at low frequency. Large specimens (length of arms ca. 280 mm) possess about 440 genital pinnules on the 10 arms. All genital pinnules are in reproductive synchrony except for the most distal ones on the arms of females. Each gonad consists of three layers: a germinal epithelium enclosing a central lumen; an outer epithelium; and an intervening genital haemal sinus. Growing oocytes project almost fully into the genital haemal sinus and then ovulate through the germinal epithelium into the ovarian lumen where they collect and mature into ova. Gametes are emitted through transient nipplelike swellings that appear on the distal surface of each genital pinnule. Unspawned eggs are phagocytized by the germinal epithelium. Breeding pattern and periodicity of ovulation were analyzed histologically at the population and individual levels, the latter by periodic removal of genital pinnules from caged animals. Breeding of the population is continuous in that females are ovulating eggs and males possess active spermatozoa throughout the year. Individual females ovulate a small quantity of eggs (ca. 23 800 maximum) about once a month and appear to spawn them within 3 days. Although breeding is continuous, aseasonal fluctuations in the level of breeding activity were detected statistically in the female population and were clearly evident in individually monitored males and females.