RELATIONSHIPS OF THE CYCLODORIPPOIDEA ORTMANN - EVIDENCE FROM SPERMATOZOAL ULTRASTRUCTURE IN THE GENERA XEINOSTOMA, TYMOLUS AND CYMONOMUS (CRUSTACEA, DECAPODA)

The spermatozoa of two genera and species of Cyclodorippidea, Xeinosto ma richeri (Xeinostominae) and Tymolus sp. (Cyclodorippinae), and one species of Cymonomus sp. (Cymonomidae) are found to constitute a disti nctive cyclodorippoid sperm-type characterized by (1) sperm anteropost eriorly depressed, mean ratio of length to width 0.54-0.63; (2) opercu lum extending to the lateral limits of the acrosome (autapomorphy of c yclodorippoids) and centrally perforate or (Cymonomus sp.) thinner; (3 ) contents of acrosome vesicle with two major horizontal zones, as in homolids and dynomenids, including a dense lower (posterior) zone; (4) perforatorium very wide (0.3 width of acrosome), anteriorly rounded, not capitate, lacking radiate projections; (5) acrosomal capsule with external projections over its posterior half; (6) slender dense filame nts extending into the perforatorium from its walls, their bases assoc iated with corrugations of its basal wall; (7) nucleus, cupping the ac rosome and cytoplasm, with well-developed posterior median process; (8 ) nuclear arms lacking microtubules; (9) cytoplasm, a narrow postacros omal band extending anteriorly as far as the operculum, associated wit h a few degenerate mitochondria. The noncapitate form of the perforato rium differs from the capitate condition in dromiids, the related dyno menids, homolids and the raninoid Lyreidus. The cyclodorippoid sperm r esembles homolid and raninoid sperm in possessing a posterior nuclear process (questionably apomorphic) and resembles homolid sperm in the h orizontal zonation of the acrosome with a dense lower zone. Features w hich resemble the sperm of raninoids are: the periacrosomal flange (Xe inostoma richeri) and smaller evaginations of the acrosome membrane (o r capsule?) (X. richeri, less distinctly Cymonomus sp. and Tymolus sp. ) reminiscent of the single acrosomal flange of Ranina and Raninoides sperm and the multiple keels of the Lyreidus sperm; and corrugations o f the wall of the perforatorial chamber, as in raninoids though with s ignificant differences. A dynomenid similarity (homoplasy?) is the dis continuous flange-like peripheral continuation of the lower zone of th e acrosome contents in Cymonomus sp.