Spermatozoal ultrastructure in three Atlantic solenocerid shrimps (Decapoda, Dendrobranchiata)

The spermatozoal ultrastructure in three solenocerid shrimps (Solenocera membranacea, S. africana, and Pleoticus muelleri) from different Atlantic locations was examined with the aim of increasing understanding of the phylogenetic relationships in the Dendrobranchiata. A considerable structural similarity between the sperm of these species and those of penaeid shrimps supports a close affinity between the Penaeidae and Solenoceridae. However, significant differences in the sperm morphology of the previously investigated sicyoniids (namely, a greater complexity of the acrosomal complex) suggest evolutionary separation of the Sicyoniidae from the assemblage Penaeidae-Solenoceridae. Two ultrastructural features distinguish the spermatozoa of the three studied solenocerids from penaeid sperm: 1) separation of the plasma and acrosome membranes at the base of the spike and anterior region of the cap, and 2) asymmetry of the acrosomal cap, which appears to be a synapomorphy of the group. No striking ultrastructural differences were found between the spermatozoa of the closely related species S. membranacea and S. africana, whereas a great number of morphological differences separate the spermatozoa of Pleoticus from those of Solenocera (e.g., shape of the acrosomal cap, structural arrangement of the contents of the whole acrosome vesicle, thickness and distribution of the cytoplasm, and external shape of the spike).