Morphology of the spermatheca, oviduct, intermediate chamber, and vagina of the adult snow crab (Chionoecetes opilio)

Abstract

The morphology of the reproductive tract of the adult female snow crab (Chionoecetes opilio) at different stages of reproductive life was examined within the framework of studies on sperm competition. Apart from an ovary and oviduct, the tract consists of an epithelium-lined spermatheca and a cuticle-lined intermediate chamber and vagina. The morphological traits of these components are markedly influenced by the degree of spermathecal loading. Several amendments to previous descriptions are necessary: (i) pouches are not a permanent feature of the spermatheca; (ii) the outer part of the spermatheca wall is a true capsule that overlies a multilayered epithelium divided into anchoring, proliferative, and secretory strata; (iii) spermathecal secretions are of the merocrine type; and (iv) the epithelium of the spermatheca is not pigmented. Tridimensional analysis revealed that the vagina connects to the intermediate chamber via a parietal opening. The intermediate chamber is a flexible structure circled dorsally by 3-5 cuticular folds that project into its lumen. The oviduct crosses the thicker terminal segment of the spermathecal epithelium with a dorsoventral incidence, to a point opposite the parietal opening of the vagina, in such a way that it delivers its contents almost directly into the intermediate chamber. Novel functional implications of these findings are hypothesized.