Ultrastructure of the sperm of the deep-sea decapod Aristeus antennatus

The sperm of Aristeus antennatus presents notable differences in relation to the two basic models of decapod crustaceans considered to date. Basically, it does not present a single appendage, or spike, characteristic of the so-called unistellate sperm of the suborder Dendrobranchiata and the infraorder Caridea of the suborder Pleocyemata. Nor does it have arms or spikes characteristic of the multistellate sperm that all belong to the Pleocyemata group. The spermatozoa of A. antennatus are composed of a nucleus and an electron-dense acrosome, which have the polarity of multistellate sperm. A number of mitochondria and vesicles are present in the cytoplasm, located between the acrosome and the nucleus. In accordance with the fine structural details, the morphology of the sperm has been described at two different levels of the male gonad, the vas deferens and terminal ampulla, and in the spermatophore placed in the thelycum of the female. Three ultrastructural changes in the acrosome (unorganized structures, tubular organization, disintegration process) and the nucleus (uncondensed, condensed, and compact) are present along the male reproductive apparatus. They first appear in a non-organized manner at the level of the vas deferens, subsequently undergo a process of structural configuration in the ampulla, and finally show disorganized structures in the spermatophore. J. Morphol. 234:79-87, 1997. © 1997 Wiley-Liss, Inc.