SPERMATOZOAL ULTRASTRUCTURE OF PENAEUS-KERATHURUS AND PENAEUS-JAPONICUS (CRUSTACEA, DENDROBRANCHIATA)

An ultrastructural comparison between the unistellate spermatozoa of t he shrimps Penaeus kerathurus and P. japonicus reveals a number of sim ilarities that are common among dendrobranchiates, but also some marke d differences which would confirm the validity of a potential use of s perm structure in systematic and phylogenetic studies. Typical morphol ogical features shared by the spermatozoa of P. kerathurus and P. japo nicus are: a membrane-bound acrosomal vesicle consisting of a cap and spike; non-membrane-bound filamentous chromatin; a perinuclear cytopla smic band including degenerative membranous organelles (mostly mitocho ndria), small vesicles with a dense core and parallel membrane lamella e. Discordant spermatozoal characteristics between both species involv e a significantly different size (ca. 5 mum in length by ca. 3 mum in diameter in P. kerathurus; ca. 8 mum in length by ca. 4.7 mum in diame ter in P. japonicus), the occurrence of intranuclear lipid droplets on ly in P. kerathurus and the presence of a deeper subacrosomal space in this species as compared to P. japonicus. It is very likely that the most significant difference between both species is, however, the appe arance of microtubule bundles in the spermatozoon of P. japonicus. So far, the occurrence of spermatozoal microtubules in decapod crustacean s appears to be restricted to reptantian species, whereby the finding of such elements in sperm of a dendrobranchiate shrimp could be of phy logenetic interest.