CONICET | Buscador de Institutos y Recursos Humanos

Abstract. Our aim was to describe the reproductive system of males and the formation ofsperm packages in the seminal receptacle (SR) of recently mated females of the arrow crabStenorhynchus seticornis. The male reproductive system was analyzed, and was describedusing light microscopy and histological and histochemical methods. The first pair of gonopodswas described by means of scanning electron microscopy. Additionally, the dehiscenceof spermatophores was tested using samples obtained from the vas deferens of males andfrom the seminal receptacle of recently mated females. Testes were tubular type, and eachvas deferens consisted of three regions: the anterior vas deferens (AVD), including a proximalportion that was filled with free spermatozoa and a distal portion contained developingspermatophores; the median vas deferens (MVD) that contained completely formed spermatophores;and the posterior vas deferens (PVD), which contained only granular secretions.The accessory gland, which was filled with secretions, was located in the transitionregion between the MVD and the PVD. The spermatophores from the MVD were of differentsizes, and none of them showed dehiscence in seawater, whereas those spermatophoresin contact with the seminal receptacle were immediately broken. The ultrastructure of thegonopods revealed the presence of denticles at the distal portion, which contribute to themechanical rupture of the spermatophore wall during the transfer of sperm. The contents ofthe PVD and accessory gland of males are transferred together with the spermatophores,and are responsible for the secretions observed among the sperm packets in the SR of thefemale. We suggest that these secretions formed the layers found in the SR of recentlymated females, and may play a role in sperm competition in arrow crabs.