The Ultrastructure of the Spermatozoon of Dromidiopsis-Edwardsi Rathbun, 1919 (Crustacea, Brachyura, Dromiidae) - Confirmation of a Dromiid Sperm Type

Abstract

The dromiid spermatozoon, as exemplified by Dromidiopsis edwardsi, Stimdromia (=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 discoidal form of the acrosome and the capitate form of the perforatorium. Dromiids differ from homolids in the greater depression of the acrosome and the form of the head of the perforatorium, thus exhibiting a distinctive dromiid sperm type. The head is bilaterally prolonged in D. edwardsi and also shows bilateral symmetry, though this is less pronounced in S. lateralis. In homolids the head of the perforatorium has the form of a horizontally disposed spiked wheel. Centrioles are unknown in dromiid sperm but are present in homolids. Nuclear arms in D. edwardsi, as in homolids, have the form of three small radial vertices. Dromiids, homolids, raninids, higher heterotremes and thoracotremes differ (homoplasically?) from lower heterotremes in lacking microtubules in the nuclear arms. Dromiid sperm lack the posterior median process of the nucleus seen in homolids, anomurans and lower heterotremes. The sperm of D. edwardsi differs from other investigated dromiid sperm in the asymmetrical location of the opercular perforation relative to the longitudinal axis of the sperm, and in more complex zonation of the acrosome vesicle. The acrosome is deeply embedded in the nucleus in D. edwardsi whereas in S. lateralis it is superficial on the nucleus. Both have an apical protuberance of subopercular material through the opercular perforation, known elsewhere only in dynomenid crabs. Sperm structure in the Dromiidae thus differs significantly from that in the Eubrachyura.