The male reproductive system in whip spiders (Arachnida: Amblypygi)

Whip spiders (Arachnida, Amblypygi), like many other soil arthropods, transfer their spermatozoa indirectly via a stalked spermatophore. While the complex courtship behavior as well as the morphological differences of spermatophores and corresponding female genitalia between taxa have received great attention in the past, comparative research on the internal reproductive system is lacking so far. In this study, the morphology of the male whip spiders of four neoamblypygid taxa has been comparatively studied via computer tomography and subsequent 3D reconstruction. We investigated four species belonging to the Neoamblypygi, that is, the phrynichid species Damon medius (Damoninae), and Euphrynichus bacillifer (Phrynichidae), the phrynid species Phrynus hispaniolae (Phrynidae), and the charontid species Charon grayi (Charontidae). The male reproductive organs consist of paired testes and two pairs of accessory glands, the ventral and lateral glands, which project their ducts anteriorly into the ventrally located unpaired spermatophore producing organ where the respective seminal and secretory reservoirs are located. While this general organization of the male reproductive system is similar among all investigated taxa, there are some notable differences in some structures. The most surprising findings include the complete absence of ventral glands in D. medius, the presence of unique spherical ventral gland reservoirs in C. grayi as well as differences in the organization of the seminal and secretory reservoirs and their connections to the inner genital slit. In addition, the secretory products of both, ventral and lateral glands, are stored in combined secretory reservoirs in E. bacillifer and P. hispaniolae. This study is the first to show that there is some morphological variation in the male reproductive system in Neoamblypygi. These results are the basis for the reconstruction of the Bauplan for the reproductive organs of the whip spiders.