THE ULTRASTRUCTURE OF THE SPERMATOZOON OF PARADYNOMENE TUBERCULATA SAKAI, 1963 (CRUSTACEA, BRACHYURA, DYNOMENIDAE) - SYNAPOMORPHIES WITH DROMIID SPERM

The dynomenid spermatozoon, exemplified here by Paradynomene tubercula ta, resembles the spermatozoa of the Dromiidae, Homolidae and lyreidin e raninoids and differs markedly from those of other crabs (the hetero treme, thoracotremes, raninines and raninoidines) in the depressed, di scoidal form of the acrosome and the capitate form of the perforatoriu m. 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 (ra tio of length to width = 0.3); (2) the capitate head of the perforator ium is bilaterally prolonged in P. tuberculata as in dromiids though s ymmetrical in homolids; (3) dynomenid and dromiid sperm lack the - alb eit variably developed - posterior median process of the nucleus seen in homolids, anomurans, raninoids and lower heterotremes; (4) P. tuber culata, like dromiids and less distinctly homolids, has an apical prot uberance of subopercular material through the opercular perforation, u nknown in other crabs, being distinct from the apical button of thorac otreme sperm; (5) a less certain synapomorphy is the anterolateral ele ctron-pale peripheral zone of the acrosome. These synapomorphies endor se a sister-group relationship of dynomenids and dromiids, P. tubercul ata sperm differs notably from the sperm of dromiids in the more compl ex 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 perfo ratorial chamber is a major difference from all examined raninids. Cen trioles are only very tentatively identifiable. Nuclear arms are absen t in glutaraldehyde fixed spermatozoa of P. tuberculata and have not b een observed in the dromiid Petalomera lateralis but are present as th ree small radial vertices in the dromiid Dromidiopsis edwardsi and in homolids. P. tuberculata resembles Petalomera lateralis in the large s ize of the sperm nucleus relative to the acrosome compared with D. edw ardsi and homolids.