Reproductive Biology and Development of Themiste Lageniformis, a Parthenogenic Sipunculan
The reproductive biology ofthe sipunculan Themiste lageniformis from Aorida is reported. The populations have temporally stable biased sex ratios with females outnumbering males 24:1. Measurements of coelomic oocytes and records of spawns define an annual cycle of reproduction. Small oocytes begin to appear in the coelom in early spring and reach maximum size by July. Spawning extends from July through January but reaches its greatest frequency during August and September. Themiste lageniformis is unique among the Sipuncula in that females produce eggs which spontaneously activate and develop into normal larvae. Multiple hypotheses are considered as explanations of this phenomenon, but only facultative parthenogenesis is supported. Themiste lageniformis is the only sipunculan species reported to use this reproductive mode.
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Document Type: Research Article
Publication date: July 1, 1987
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