Histological Remarks of the Uterus of Sympterygia acuta (Garman, 1877) and Sympterygia bonapartii (Müller & Henle, 1841) (Chondrichthyes; Rajidae)

Chondrichthyes constitute a conserve and vulnerable clade of increasing importance. However, there is scarce knowledge about the morphological aspects of the reproduction, so that only one work exists about the structure of the gravid uterus of an oviparous species. The work presented here describes the morphological, histological and histochemical remarks of the uterus of two Rajids of the Sympterygia genus along the life cycle. Both species presented paired uteri that lead independently to a common urogenital sinus. The uteri of immature females are filiform, translucent and unspecialized tubes. When sexual development starts, all the genital system displays a transitional and progressive change. In all studied females, independently of the maturing stage, the same four layers were present all over the uterus: a mucosa, which comprises the lining epithelium and lamina propria, a submucosa, a muscular and a serosa. The major changes in the structure of the uterus along the life cycle occur in the mucosa. The uteri of mature, gravid and non-gravid, females presents three distinguishable areas, cranial, medial and caudal, that vary both in the structure and histochemistry of the mucosa and in the thickness of the muscular layer. The results presented here are discussed in a physiological, adaptive and phylogenetic context.