Penis morphology as a distinctive character of the murine opossum group (Marsupialia Didelphidae): a preliminary report

Penis morphology, associated with other features, has been suggested as an identification trait and an additional variable useful for systematic arrangement of the murine opossum group. This is a numerically important group of American marsupials, with similar external characters but without yet a systematically arranged source list. The penis morphology of four species, Micoureus cinereus, Gracilinanus agilis, Marmosops incanus, and Marmosa murina is described. The internal anatomical aspects are similar in the four species. The main differences between the species are the form of the tip of the glans and the length of the urethral grooves. The four species present distinctive external characters of the penis that permit their identification in the field and could possibly be used as a taxonomic tool. Nevertheless, additional studies involving other species of the group are needed in order to determine the value of this feature in the systematics of the group as a whole.