| Summary: | Observations on reproductive biology of four species of Perkinsiana (Polychaeta: SabeIlidae) are reported and examined at the light of both phylogenetic and ecological factors. Perkinsiana littoralis and P. borsibrunoi, collected sympatrically on the shelf (100-800 m depth) ofthe Eastem Weddell Sea, Antarctica, are gonochoric, and females show oocytes at different stages of maturation; P. littoralis contains a higher number of larger eggs (150-200 j.U11) than P. borsibrunoi (100-150 j.U11). Males ofP.littoralis show a mature sperm with a typical ect-aquasperm morphology; whereas mature males ofP. borsibrunoi were not found, suggesting a different timing ofreproduction between these two sympatric species. Perkinsiana antarctica, collected in the intertidal and shallow subtidal zones ofthe Straits ofMagellan, is a simultaneous hermaphrodite, incubating its embryos and larvae within the branchial crown. Its mature spermatozoa show an ovaI nucleus and a long and pointed acrosome. Finally, in Perkinsiana milae, collected in the Ross Sea, Antarctica (75-200 m depth), gametes were never found. In this last species some large individuals with an evident body constriction near the pygidium, as well as many small individuals characterized by a few adult segments and small, regenerating branchial crown and pygidium were observed. These findings may indicate the occurrence of asexual reproduction by scissiparity. Present observations demonstrate the high variability in reproductive characters within the species assigned to Perkinsiana. Incubation in P. antarctica, which seems not to be constrained by size, and possible asexual reproduction in P. milae, are discussed in relation with ecological factors. Comparison with data on reproductive biology of other species assigned to Perkinsiana allowed the identification of possible monophyletic groups.
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