Ultrastructure of the spermatozoon of Potamonautes perlatus sidneyii (Heterotremata, Brachyura, Crustacea)

ENGLISH ABSTRACT: Features of the spermatozoon of Potamonautes which are general for heterotremes and endorse its inclusion in the Heterotremata are: extension of the subacrosomal chamber almost to the anterior apex of the sperm; presence of an acrosome ray zone; and presence of a thickened ring (though here vestigial) where the capsule surrounds the base of the subacrosomal chamber. A feature shared with 'higher' heterotremes is the restriction of cytoplasm to the periacrosomal region, the arms being nuclear only; and loss of a posterior median process, containing chromatin, which is present in raninids and majids. Peculiarities of Potamonautes relative to other heterotremes (and paguroid anomurans) are (i) the indistinct substructure of the acrosomal ray zone; (ii) absence of a recognizable inner acrosomal zone differentiated from this, and (iii) reduction of the thickened ring, the latter trend being taken to completion in grapsid Thoracotremata. Unknown in other Brachyura are (iv) a rim-like electron pale expansion around the operculum and (v) the elongate condition of at least one of the two centrioles. These five unusual features are regarded as apomorphies of Potamonautes. **************** AFRIKAASNE OPSOMMING: Eienskappe van die sperms van Potamonautes wat algemeen is vir heterotreme en sy insluiting in die Heterotremata bevestig, is: uitbreiding van die subakrosomale kamer tot bykans die voorste (anterior) apeks van die sperm; teenwoordigheid van 'n akrosomale straalstreek; en die teenwoordigheid van 'n verdikte ring (hoewel vestigiaal) waar die kapsel die basis van die subakrosomaalkamer omring. 'n Eienskap wat gedeel word met 'ho r' heteroteme is die beperking van sitoplasma tot die periakrosomale streek, met die arms slegs kernagtig; en die verlies van 'n agterste (posterior) mediane uitsteeksel wat chromatien bevat en wat teenwoordig is by raninide en majide. Eienaardighede by Potamonautes in vergelyking met ander heterotreme (en paguro ede anomuras) is (i) die onduidelike substruktuur van die akrosomale straalstreek, (ii) afwesigheid van 'n herkenbare binneste akrosomale streek wat hiervan gedifferensieer is, en (iii) reduksie van die verdikte ring, laasgenoemde neiging word meer voltooid gevind by die grapside Thoracotremata. Wat onbekend is by ander Brachyura is (iv) 'n rifagtige uitbreiding rondom die operkulum en (v) die verlengde toestand van ten minste een van die twee sentriole. Hierdie vyf ongewone eienskappe word as apomorfie van Potamonautes beskou.