ULTRASTRUCTURE OF THE SPERM OF THE DEEP-SEA DECAPOD ARISTEUS-ANTENNATUS

The sperm of Aristeus antennatus presents notable differences in relat ion to the two basic models of decapod crustaceans considered to date. Basically, it does not present a single appendage, or spike, characte ristic of the so-called unistellate sperm of the suborder Dendrobranch iata 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 t he polarity of multistellate sperm. A number of mitochondria and vesic les are present in the cytoplasm, located between the acrosome and the nucleus. In accordance with the fine structural details, the morpholo gy of the sperm has been described at two different levels of the male gonad, the vas deferens and terminal ampulla, and in the spermatophor e placed in the thelycum of the female. Three ultrastructural changes in the acrosome (unorganized structures, tubular organization, disinte gration 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, subsequent ly undergo a process of structural configuration in the ampulla, and f inally show disorganized structures in the spermatophore. (C) 1997 Wil ey-Liss, Inc.