First investigation of the spermatozoa of a species of the superfamily Scorpionoidea (Opistophthalmus penrithorum, Scorpionidae) with a revision of the evolutionary and phylogenetic implications of sperm structures in scorpions (Chelicerata, Scorpiones)

Despite their enormous diversity, spermatozoa are only scarcely studied in arachnids. In spiders, harvestmens and mites, it has been shown that spermatozoa are a potential source of characters which can support, contradict or even resolve previous phylogenetic hypotheses. In scorpions, the spermatozoa of most superfamilies (except the taxon-rich Scorpionoidea and the obscure Chaeriloidea) are known in more or less detail revealing considerable differences, especially between buthid and non-buthid scorpions. However, this apparent diversity is based on descriptions of only 12 scorpion species. In the present study, we investigated the spermatozoa of a species of the superfamily Scorpionoidea (Opistophthalmus penrithorum, Scorpionidae) for the first time by means of light and electron microscopy. The scorpionoid spermatozoa are characterized by (1) an asymmetrical, cap-like acrosomal vacuole at the tip of the anterior pole of the nucleus, (2) a short acrosomal filament, (3) a nucleus, which is tapered anteriorly, (4) a midpiece with 5-6 mitochondria and (5) an axoneme with a 9 + 0 pattern with a helical beating movement. Moreover, we provided a detailed description regarding sperm packages, that consist of approximately 250 sperm cells bent in the midpiece region, and lack a secretion sheath. Overall, the organization and general morphology of spermatozoa of the observed species is similar to what is known for non-buthids. To evaluate the evolutionary and phylogenetic implications of our results, we performed a comparative revision of sperm morphology in scorpions for the first time and proposed potential informative characters (six for spermatozoa and six for sperm packages). We concluded so far that sperm structure in scorpions could provide new characters for future comprehensive phylogenetic studies of the order, and that they could even represent synapomorphies not only for the order but for the major scorpion clades as well. © 2009 Blackwell Verlag GmbH.