Ultrastructural observations of spermatozoa of several tetragnathid spiders with phylogenetic implications (Araneae, Tetragnathidae).

The present study reports on the ultrastructure of spermatozoa and spermatogenesis of 12 tetragnathid spiders (10 Tetragnatha species [T. boydi, T. dearmata, T. extensa, T. montana, T. nigrita, T. obtusa, T. pinicola, T. reimoseri, T. shoshone, T. striata]; Pachygnatha listeri and Metellina segmentata). All species develop typical cleistospermia with a coiled nucleus in the center and a coiled axoneme in the periphery of the cell. Remarkable differences in the sperm ultrastructure of the investigated species comprise the shape of the main sperm cell components (nucleus, acrosomal complex, implantation fossa, and centriolar complex). Within the observed Tetragnatha species, three types of sperms were characterized: T. montana-type, T. boydi-type, and T. striata-type. The highly derivative T. montana-type is characterized by the following remarkable features: an extremely elongated nucleus, shaped like a corkscrew and twisted around the axoneme (before coiling); a deep implantation fossa; a corkscrew-shaped acrosomal vacuole; after the coiling process, the nucleus is coiled five to six times in the center of the spermatozoon and the axoneme is coiled five to six times peripheral to the nucleus. The T. boydi-type hardly differs from the T. montana-type, but is remarkable due to the triangular-shaped nucleus (in cross section). The T. striata-type differs especially by a peculiar acrosomal vacuole with a long, slightly curved process and a short appendix, as well as a nucleus that describes only three loose coils around the axoneme (before coiling). The spermatozoa of Pachygnatha listeri and especially Metellina segmentata differ strikingly from the described Tetragnatha-types and are similar to more primitive araneomorph spermatozoa, such as Hypochilus pococki. The described Tetragnatha-types completely correspond with Okuma's (1988a,b, J Fac Agr Kyushu U 32:165-181, 32:183-213) classification of Tetragnatha species. Furthermore, our results suggest an early derivative systematic position of Pachygnatha within Tetragnathinae and the position of Metellina within the Tetragnathidae.