Branchiopods represent one of the most ancient crustacean lineages that still include extant representatives, many of which are capable of a wide array of reproductive mechanisms. Specifically, members of the branchiopod suborder Spinicaudata have been found to display at least four different mating system strategies: dioecy, androdioecy, hermaphroditism, and parthenogenesis. Although genetic/molecular, morphological, and sex ratio data have dominated the field in terms of understanding mating systems within the Spinicaudata, cellular and histological evidence have recently started to unveil fundamental questions regarding reproductive biology within various Spinicaudata groups. As such, a clearer understanding of Spinicaudata reproductive biology has aided in more accurate assignment of mating system type within many clam shrimp populations. The purpose of this study was to investigate basic reproductive biology and associated mating systems in multiple clam shrimp species not previously studies using histological or cellular techniques.
Based on the histological and cellular findings of this study, anatomical verification is herein provided that supports many previously inferred mating systems in various clam shrimp populations. Also, this study provides anatomical
support that can be used to infer likely mating system mechanisms in representative populations of clam shrimp species not previously investigated for reproductive mode. Lastly, anatomical evidence is provided for the first time that suggests that individuals from a Cyzicus gynecia population (previously thought to be asexual) are, in fact, selfing-hermaphrodites. The anatomical data generated from this study for multiple Spinicaudata representatives suggests a useful technique that can be used in conjunction with current commonly used methodologies (namely genetic/molecular data, sex ratios, and morphological evidence) to gain a clearer understanding of the various mating systems found within these unique, freshwater invertebrates.