The ultrastructure of the spermatozoon ofParadynomene tuberculata Sakai, 1963 (Crustacea, Brachyura, Dynomenidae): Synapomorphies with dromiid sperm
© Biologische Anstalt Helgoland 1992
The dynomenid spermatozoon, exemplified here byParadynomene 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 inP. 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 ofP. tuberculata and have not been observed in the dromiidPetalomera lateralis but are present as three small radial vertices in the dromiidDromidiopsis edwardsi and in homolids.P. tuberculata resemblesPetalomera lateralis in the large size of the sperm nucleus relative to the acrosome compared withD. edwardsi and homolids.