Spermatozoa and spermiogenesis of Liphistius cf. phuketensis (Mesothelae, Araneae, Arachnida) with notes on phylogenetic implications

The present study deals with the spermatozoa and spermiogenesis of Liphistius cf. phuketensis, a representative of the most primitive and enigmatic spider group Mesothelae. The general organization of the spermatozoa is very similar to the condition known from Amblypygi supporting a sister-group relationship between Araneae and Amblypygi. Besides plesiomorphic characters such as, e.g., an elongated and corkscrew shaped nucleus, the sperm cells are characterized by several apomorphic characters, e.g., the giant body and conspicuous membranous areas which are formed at the end of spermiogenesis. As the transfer form, coenospermia are formed at the end of spermiogenesis, which strongly supports the idea that this type of sperm aggregation is the primitive transfer form within spiders. A very remarkable character of the spermatozoa of some groups of arachnids is the coiling of the main cell organelles at the end of spermiogenesis. Previously, the Mesothelae were believed to be the only spider group which does not show a complete coiling of the main cell organelles. With the present study the first evidence of a complete coiling of spermatozoa within this primitive spider group could be documented, indicating that this character is part of the ground pattern of spider spermatozoa. Consequently, the incomplete coiling seems to be a synapomorphy of certain species of Mesothelae, which sheds new light on the discussion of the phylogenetic relationships of this group.