Spermatozoal ultrastructure of the hermit crab Loxopagurus loxochelis (Moreira, 1901) (Decapoda: Anomura: Diogenidae) from the southwestern Atlantic

Abstract

The spermatozoal morphology of Loxopagurus loxochelis exhibits characters shared by other paguroids: complex concentrically zoned acrosome vesicle, capped by an electron-dense operculum and posteriorly penetrated by a large perforatorial chamber, and three microtubular arms emanating from the cytoplasm. The general sperm cell dimensions and arrangement of the acrosome in L. loxochelis are similar to those previously described for three species of Calcinus. However, Loxopagurus lacks a defining autapomorphy of this genus: splitting of the anterior end of the perforatorial chamber into many obvious fingers. The only unique character observed in the sperm of Loxopagurus is the presence, in the cytoplasm, of a bulge filled with small tubules on the side of the acrosome. This structure could be an artifact or possibly a parasitic bacterial infection. In conclusion, L. loxochelis sperm morphology does not demonstrate any clear autapomorphies, but seems to separate from the other genera in the Diogenidae by the absence of their defining sperm characters (e.g. anterior perforatorial fingers and microvillar projections). It appears most similar to the genus Calcinus, and more superficially Strigopagurus, although its spermatophore morphology seems to indicate a doser relationship with Clibanarius. The combination of spermatophore and spermatozoal characters clearly places it in the Diogenidae, and supports its monotypic status.