MEPS 181:201-214 (1999)  -  doi:10.3354/meps181201

ABSTRACT: We examined the reproductive biology of a polynoid polychaete commensal in mussel mantle cavities (Branchipolynoe cf. seepensis) and of a polynoid polychaete that is free-living among those same mussels (Opisthotrochopodus n. sp.). Specimens of each species were collected from 2 different sites (Eiffel Tower and Sintra; ~400 m apart) within the Lucky Strike hydrothermal field. Both species exhibit sexual dimorphism, with varying numbers of pairs of nephridial papillae. In B. cf. seepensis, sexual dimorphism also includes a difference in size, with females larger than males. Contrary to our expectations, the reproductive biology of both species is very similar. Sperm heads are elongate, suggesting some mode of sperm transfer or storage. Females of both species contain mature sperm and there is evidence of internal fertilization. Maximum oocyte diameters are large (>390 µm), from which we infer non-planktotrophic development; oogenesis is intraovarian and suggests rapid oocyte development. Oocyte size-frequency distributions and population size structure suggest a pattern of asynchronous gametogenesis. We found no substantive evidence for site-specific variations in reproductive biology in either species.

KEY WORDS: Hydrothermal vent · Polychaete reproduction · Polynoid