Socotrapotamon socotrense (Hilgendorf in Taschenberg, 1883)

Klaus, Sebastian & Brandis, Dirk, 2011, Evolution of sperm morphology in potamid freshwater crabs (Crustacea: Brachyura: Potamoidea), Zoological Journal of the Linnean Society 161 (1), pp. 53-63 : 56-57

SOCOTRAPOTAMON SOCOTRENSE ( FIG. 1A–E, 1C; TABLE 2)

Socotrapotamon socotrense has the smallest acrosome size of the Potamidae (AL = 2.76 ± 0.11 Mm, AW = 1.90 ± 0.16 Mm, N = 7). The acrosome is strongly depressed (AW/AL = 0.7 ± 0.05). The centrally bulging operculum is perforate and not connected via tongue and groove to the acrosomal zones beneath. The very prominent inner acrosomal zone and the distinct acrosome ray zone bulge outwards. Apically, towards the operculum, the acrosome ray zone is covered with electron-dense material. There is an electron-lucent ring that surrounds the basal opening of the perforatorial chamber. The coenospermic spermatozoa are densely packed into spermatophores. The spermatophore wall is formed by two layers: an outer, electrondense layer, and an inner, less electron-dense layer ( Fig. 1E ).

The wide inner acrosomal zone, the electron dense ‘cap’ on the acrosome ray zone, and the electronlucent ring surrounding the proximal end of the perforatorial chamber represent unique sperm characters within the Potamidae .

Figures

Figure 1. Transmission electron microscopy (TEM) of potamid spermatozoa. A–E, Socotrapotamon socotrense. A, longitudinal sagittal view; the white line points to the perforate operculum. B, coenospermic spermatophore. C, cross section. D, electron-lucent ring around the opening of the perforatorial chamber. E, spermatophore wall. F–J, Potamon fluviatile. F, spermatophore wall. G, coenospermic spermatophore. H, longitudinal sagittal section (slightly transverse) and cleistospermic spermatophore. J, cross section. Scale bars: 1 Mm, or as indicated. Abbreviations: ar, acrosome ray zone; ia, inner acrosomal zone; nu, nucleus; oa, outer acrosomal zone; op, operculum; pc, perforatorial chamber; sw, spermatophore wall.