Spermatozoal ultrastructure of Penaeus kerathurus and Penaeus japonicus (Crustacea,Dendrobranchiata)

Summary An ultrastructural comparison between the unistellate spermatozoa of the shrimps Penaeus kerathurus and P. japonicus reveals a number of similarities that are common among dendrobranchiates, but also some marked differences which would confirm the validity of a potential use of sperm structure in systematic and phylogenetic studies. Typical morphological features shared by the spermatozoa of P. kerathurus and P. japonicus are: a membrane-bound acrosomal vesicle consisting of a cap and spike; non-membrane-bound filamentous chromatin; a perinuclear cytoplasmic band including degenerative membranous organelles (mostly mitochondria), small vesicles with a dense core and parallel membrane lamellae. Discordant spermatozoal characteristics between both species involve a significantly different size (ca. 5 m in length by ca. 3 m in diameter in P. kerathurus; ca. 8 m in length by ca. 4.7 m in diameter in P. japonicus), the occurrence of intranuclear lipid droplets only 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 appearance of microtubule bundles in the spermatozoon of P. japonicus. So far, the occurrence of spermatozoal microtubules in decapod crustaceans appears to be restricted to reptantian species, whereby the finding of such elements in sperm of a dendrobranchiate shrimp could be of phylogenetic interest.