The dynomenid spermatozoon, exemplified here by Paradynomene tuberculata, resembles the spermatozoa of the Dromiidae, Homolidae and lyreidine raninoids and differs markedly from those of other crabs (the heterotreme, thoracotremes, raninines and raninoidines) in the depressed, discoidal form of the acrosome and the capitate form of the perforatorium. Four or five apparent dynomenid - dromiid sperm synapomorphies are recognizable.
(1) Dynomenids (P. tuberculata) and dromiids differ from homolids and lyreidines in the greater depression of the acrosome (ratio of length to width = 0.3);
(2) the capitate head of the perforatorium is bilaterally prolonged in P. tuberculata as in dromiids though symmetrical in homolids;
 (3) dynomenid and dromiid sperm lack the - albeit variably developed - posterior median process of the nucleus seen in homolids, anomurans,  raninoids and lower heterotremes;
(4) P. tuberculata, like dromiids and less distinctly homolids, has an apical protuberance of subopercular   material through the opercular perforation, unknown in other crabs, being   distinct from the apical button of thoracotreme sperm;
(5) a less certain   synapomorphy is the anterolateral electron-pale peripheral zone of the   acrosome.
These synapomorphies endorse a sister-group relationship of   dynomenids and dromiids, P. tuberculata sperm differs notably from the   sperm of dromiids in the more complex zonation of the acrosome. The   perforatorium lacks the radial rays ("spiked wheel") of homolid sperm and   does not show the "amoeboid' form seen in lyreidines. Absence of internal   corrugations of the perforatorial chamber is a major difference from all   examined raninids. Centrioles are only very tentatively identifiable.   Nuclear arms are absent in glutaraldehyde fixed spermatozoa of P.   tuberculata and have not been observed in the dromiid Petalomera lateralis   but are present as three small radial vertices in the dromiid Dromidiopsis   edwardsi and in homolids. P. tuberculata resembles Petalomera lateralis in   the large size of the sperm nucleus relative to the acrosome compared with   D. edwardsi and homolids.