Ultrastructural analysis of sperm storage and morphology of the oviducal gland in the Oman shark, Iago omanensis (Triakidae)

Abstract

Sperm storage, oviducal gland morphology and ultrastructure are described in pregnant females of the viviparous placental Oman shark, Iago omanensis, that were harbouring uterine eggs, embryos or fetuses. Zonation of the gland from anterior to posterior is similar to those previously described for other elasmobranchs and is designated as club, papillary, baffle and terminal zones. The terminal zone has two regions, the first comprising short tubules adjacent to the baffle zone that are positive by periodic acid–Schiff. Posteriorly, the terminal zone has deep clefts that terminate as dilated recesses harbouring laterally arrayed bundles of spermatozoa surrounded by a flocculent matrix. Sperm were found in the terminal zone of all animals examined. Samples were not available throughout gestation, so it is not known whether the sperm is stored from a single insemination or from multiple matings. The club zone stains positive by the periodic acid–Schiff method, as does the papillary zone. The last lamella of the papillary zone is positive by Alcian blue staining. The secretory product of the baffle zone is the tertiary egg envelope that encloses the developing embryo during much of gestation.