Quantitative and ultrastructural studies on the reproductive biology of the polychaete Pholoe minuta in Galway Bay

Abstract

Previous works by the present authors have identified, in a qualitative fashion, the reproductive cycle of Pholoe minuta (Fabricius) in inner Galway (53°13.5′N; 9°7′W). This quantitative, histological study, carried out over the period late May 1981 to late April 1982, shows that P. minuta is polytelic (two to three annual spawnings in an individual's lifespan). Individuals become sexually mature for the first time when approaching 3 yr of age. Estimates were made of the size of the reproductively active population (47 to 49%), sex ratio (1:1), duration (10 to 11 mo) and pattern (unimodal) of gametogenesis and fecundity levels (210 198 eggs m-2). Maturation (mean oocyte size=85 μm) and spawning (for 1 wk during late March through early April) were shown to be synchronised. Throughout oogenesis, follicle cells play an important role in binding together oocyte clusters, and desmosomal contacts are evident between oocyte and follicle cell plasmalemmas. No evidence for the synthesis of yolk precursors in the follicle cell cytoplasm was discovered. Oocytes are rich in Golgi apparatuses (yolk synthesising) and nuclear pores are numerous. Rough endoplasmic reticulum is distended in nature. Egg envelope development does not appear to commence until after the onset of vitellogenesis. Mature spermatozoa are of the primitive bullet-shaped type, with an unmodified acrosome. A possible method of elevation membrane formation is described.