THE ULTRASTRUCTURE OF THE SPERMATOZOON OF DROMIDIOPSIS-EDWARDSI RATHBUN, 1919 (CRUSTACEA, BRACHYURA, DROMIIDAE) - CONFIRMATION OF A DROMIIDSPERM TYPE

The dromiid spermatozoon, as exemplified by Dromidiopsis edwardsi, Sti mdromia (=Petalomera) lateralis and Dromidia antillensis, accords with that of the Homolidae and differs markedly from spermatozoa of other crabs (the raninid-heterotreme-thoracotreme assemblage) in the discoid al form of the acrosome and the capitate form of the perforatorium. Dr omiids differ from homolids in the greater depression of the acrosome and the form of the head of the perforatorium, thus exhibiting a disti nctive dromiid sperm type. The head is bilaterally prolonged in D. edw ardsi and also shows bilateral symmetry, though this is less pronounce d in S. lateralis. In homolids the head of the perforatorium has the f orm of a horizontally disposed spiked wheel. Centrioles are unknown in dromiid sperm but are present in homolids. Nuclear arms in D. edwards i, as in homolids, have the form of three small radial vertices. Dromi ids, homolids, raninids, higher heterotremes and thoracotremes differ (homoplasically?) from lower heterotremes in lacking microtubules in t he nuclear arms. Dromiid sperm lack the posterior median process of th e nucleus seen in homolids, anomurans and lower heterotremes. The sper m of D. edwardsi differs from other investigated dromiid sperm in the asymmetrical location of the opercular perforation relative to the lon gitudinal axis of the sperm, and in more complex zonation of the acros ome vesicle. The acrosome is deeply embedded in the nucleus in D. edwa rdsi whereas in S. lateralis it is superficial on the nucleus. Both ha ve an apical protuberance of subopercular material through the opercul ar perforation, known elsewhere only in dynomenid crabs. Sperm structu re in the Dromiidae thus differs significantly from that in the Eubrac hyura.