ULTRASTRUCTURE OF THE SPERMATOZOA OF HYMENOSOMATIDAE (CRUSTACEA, BRACHYURA) AND THE RELATIONSHIPS OF THE FAMILY

The spermatozoa of the genus Odiomaris Ng and Richer de Forges, 1996 ( =Amarinus Lucas, 1980) have the components typical of eubrachyuran (He terotremata + Thoracotremata) sperm, but differ significantly from all other investigated eubrachyurans in at least ten characteristics: (1) presence of an epiopercular dome; (2) separation of all but the centr al region of the operculum from the remainder of the acrosome by an in fra-opercular rim; (3) the fact that the acrosome is smaller in volume than the nucleus; (4) the acrosome is strongly emergent from the nucl eus, being surrounded only basally by nuclear material; (5) the cytopl asmic sheath, ending anteriorly with the nucleus, is also basal; (6) d ivision of the acrosome contents into an inner and outer acrosome zone is scarcely apparent in longitudinal section as the inner zone is nar row and of doubtful homology; (7) the thin, putative inner acrosome zo ne is anteriorly almost septate owing to several longitudinal corrugat ions; (8) basally there is a unique ''fringe zone''; (9) the acrosome, including the epinuclear dome, is longer than wide; (10) the unique h elical and posterolateral disposition of the nuclear arms. From a pure ly spermatological viewpoint, Odiomaris (as exemplified by O. pilosus and O. estuarius), and provisionally the Hymenosomatidae, are thus exc luded from the Thoracotremata, in which they were formerly placed, nor are they readily placeable in the Heterotremata.