Dorippids are Heterotremata: Evidence from ultrastructure of the spermatozoa ofNeodorippe astuta (Dorippidae) andPortunus pelagicus (Portunidae) Brachyura: Decapoda

Ultrastructural comparison between the sperm of the dorippid crabNeodorippe astuta (Fabricius, 1793) and the portunidPortunus pelagicus (Linnaeus, 1766) from Queensland, Australia, supports placement of dorippids with portunids and their relatives in the heterotreme section of the Eubrachyura (the Heterotremata - Thoracotremata or the Oxyrhyncha - Cancridea - Brachygnatha assemblage) and not withRanina ranina (in the Archaeobrachyura or the Oxystomata). Similarities between spermatozoa ofN. astuta and ofP. pelagicus (and other Eubrachyura) andR. ranina include: the large spherical, multi-layered, capsule-bound acrosome vesicle; the electron-dense operculum capping the vesicle; an invaginated core, or perforatorium; concentric zonation of the contents of the vesicle; a layer of cytoplasm, between the acrosome vesicle and the nucleus, which contains mitochondria (mostly degenerating) and lattice-like lamellar complexes or membrane remnants; a diffuse nucleus which is bounded externally by a combined nuclear and plasma membrane and cups the scanty cytoplasm and the large acrosome vesicle; and lateral arms into which the chromatin extends. Characteristic eubrachyuran features of theN. astuta sperm absent fromR. ranina are the long perforatorium (short and conical with a unique subacrosomal chamber inR. ranina) extending almost to the operculum; presence in the perforatorium of longitudinally arranged convoluted tubules; a zone of acrosomal rays forming the outer part of an inner dense zone; the presence of a thickened ring surrounding the basal part of the perforatorium; and, basally, two centrioles (absent fromR. ranina but also from some eubrachyurans). The sperm ofN. astuta is more similar to that ofP. pelagicus than to that of other investigated Brachyura. A heterotreme status ofN. astuta is thus unequivocally supported. Both species lack the posterior median process seen in the nucleus of majids andR. ranina.