ABSTRACT

The use of spermatozoal characters in elucidating animal phylogeny (spermiocladistics) has been successfully applied in the decapod crustaceans. Most of the studies investigating decapod sperm morphology have been published in the last 18 years and cover 100% of the decapod infraorders, 50% of the families, and approximately 10% of the extant genera, but only 2% of the described, extant species. There is great diversity in sperm morphology within the Crustacea, but overall decapod spermatozoa are quite conservative in comparison. Still, it is difficult to describe a typical decapod sperm cell. Decapod sperm are unusual for several reasons: 1) they are aflagellate (lack a true 9 + 2 flagellum), although microtubular processes are often present; 2) there is no reliable record of motility for any individual sperm cell; 3) the acrosome vesicle is not Golgi-derived as in all other described acrosomes of sperm in the animal kingdom, instead being derived from endoplasmic reticulum vesicles; 4) the decapod sperm nuclear protein is unique, with all other animal sperm nuclear proteins falling into four other categories; 5) the sperm nucleus is composed of diffuse, filamentous, heterogeneous chromatin fibers rather than being uniformly dense; and 6) the mitochondria are degenerate in mature sperm cells. I surveyed spermatozoal characters across the investigated decapod crustaceans, highlighting those of phylogenetic utility, such as acrosome vesicle presence, shape, dimensions and size, and internal complexity; nuclear morphology and shape; and microtubular arm presence, number, and origin. Particular spermatozoal characters, or suites of characters, that define various decapod taxa are provided, and their utility to phylogenetic construction is discussed.