Comparative morphology of the spermatophores and spermatozoa of three Amazon freshwater crabs (Decapoda, Brachyura, Trichodactylidae)

Abstract

The ultrastructure of spermatophores and spermatozoa of freshwater crabs are little known, and a description of characters unique to this taxon is lacking. In this study, we describe and compare the ultrastructure of spermatophores and spermatozoa of Dilocarcinus pagei, Zilchiopsis oronensis and Valdivia serrata. In addition, we perform a comparative analysis with other freshwater crab species described in the literature. All species studied presented predominantly coenospermic spermatophores, in addition Z. oronensis and V. serrata also presented some cleistospermic spermatophores; which are described here for the first time in Trichodactylidae. The spermatozoa of the three species share a pattern found in the Brachyura, however, we found common traits for Trichodactylidae. The operculum is thick, protruding and imperforate with the presence of a prominent subopercular ring. The shape of the operculum is roundish in D. pagei and more triangular in Z. oronensis and V. serrata. The perforatorial chamber is panduriform in D. pagei and Z. oronensis, and oblong in V. serrata. The membrane of the perforatorial chamber in D. pagei has numerous shallow corrugations and short perforatorial filaments, while Z. oronensis and V. serrata have fewer, almost indistinguishable corrugations and long perforatorial filaments. All three species have a marked lateral expansion of the base of the perforatorial chamber and overall truncation of the acrosome vesicle, in Z. oronensis and V. serrata, absence of an acrosome ray zone, developed thickened ring and a thick nucleo-cytoplasmic plate, being obviously lamellar in D. pagei and homogeneous in Z. oronensis and V. serrata. The spermatozoa presents similar characteristics between Trichodactylidae and other freshwater crab families opening the possibility of unit all heterotreme freshwater crab families as a single group. The probably Trichodactylidae autapomorphies, that diverges from all other freshwater crabs, reinforce the hypothesis that the trichodactylids derived later as an independent lineage of freshwater crabs.