Microscopic Anatomy of the Male Reproductive System in Echinolittorina peruviana (Mollusca: Caenogastropoda)

Echinolittorina peruviana (Lamarck, 1822), a gonochoric representative of the Littorinidae on the SE Pacific coast, has a male reproductive system adapted for internal fertilization. We describe this system at both macroand microscopic levels, particularly the compartmentalized organization of the gonad, and the morphology of the penis. The male reproductive system has a variegated conical gonad-digestive gland complex. The gonad presents three compartments, 1) gametogenic acinar among the glandular acini, 2) periacinar with a layer of fusiform somatic cells and, 3) interacinar with glycogen storage cells shared with glandular acini. Spermatogenesis occurs within the acinar gametogenic compartment, with the germinal line organized in centripetal form towards the lumen. The seminal vesicle stores the products of spermatogenesis; in its cephalic region the euspermatozoa are united to the epithelium and the paraspermatozoa are distributed in the lumen. A short duct connects the seminal vesicle to the prostate gland that is open to the pallial cavity over its entire length. The anterior zone of the prostate gland is joined to the cervical spermatic groove that runs along the neck of the snail through the right pallial region; this continues as the penile spermatic groove, ascending from the base to the point of the penis. The penis is acutely conical and unpigmented; towards the anterior and adjacent to its base there is a glandular complex with a mamilliform process and a discoidal glandular region. The secretion from the discoidal region is transformed in a spicule of unknown function, whose histology is described here for the first time. The mamilliform process is formed by the spicular projection and a connective-muscle tissue band which surrounds it and separates it from the discoidal follicular glandular region; the follicular secretion crosses this band and is incorporated into the epithelium which lines the interior of the process.