Jamieson, B.G.M., Guinot, D. and Richer de Forges, B. 1994b. Relationships of the Cyclodoroippidea Ortmann: evidence from spermatozoal ultrastructure in the genera Xeinostoma, Tymolus and Cymonomus (Crustacea, Decapoda). Invertebrate Reproduction and Development 26, 153-164.

The spermatozoa of two genera and species of Cyclodorippidea, Xeinostoma
  richeri (Xeinostominae) and Tymolus sp. (Cyclodorippinae), and one species
  of Cymonomus sp. (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 (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 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
  raninoid Lyreidus. 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
  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 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 in Cymonomus sp.