The spermatozoa of two genera and species of Cyclodorippidea,Xeinostoma richeri(Xeinostominae) andTymolussp. (Cyclodorippinae), and one species ofCymonomussp. (Cymonomidae) are found to constitute a distinctive cyclodorippoid sperm-type characterized by (1) sperm anteroposteriorly depressed, mean ratio of length to width 0.54–0.63; (2) operculum extending to the lateral limits of the acrosome (autapomorphy of cyclodorippoids) and centrally perforate or (Cymonomussp.) 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 filaments extending into the perforatorium from its walls, their bases associated with corrugations of its basal wall; (7) nucleus, cupping the acrosome and cytoplasm, with well-developed posterior median process; (8) nuclear arms lacking microtubules; (9) cytoplasm, a narrow postacrosomal band extending anteriorly as far as the operculum, associated with a few degenerate mitochondria. The noncapitate form of the perforatorium differs from the capitate condition in dromiids, the related dynomenids, homolids and the raninoidLyreidus. The cyclodorippoid sperm resembles homolid and raninoid sperm in possessing a posterior nuclear process (questionably apomorphic) and resembles homolid sperm in the horizontal zonation of the acrosome with a dense lower zone. Features which resemble the sperm of raninoids are: the periacrosomal flange (Xeinostoma richeri) and smaller evaginations of the acrosome membrane (or capsule?) (X. richeri, less distinctlyCymonomussp. andTymolussp.) reminiscent of the single acrosomal flange ofRaninaandRaninoidessperm and the multiple keels of theLyreidussperm; and corrugations of the wall of the perforatorial chamber, as in raninoids though with significant differences. A dynomenid similarity (homoplasy?) is the discontinuous flange-like peripheral continuation of the lower zone of the acrosome contents inCymonomussp.