Paepke, H.-J., Arendt, K.

Nannostomus marginatus mortenthaleri new subspec. from Peru (Teleostei: Lebiasinidae)

Summary: A new subspecies of Nannostomus marginatus Eigenmann, 1909 is described from the Rio Nanay basin of the departemento Loreto, Peru. The new subspecies differs from the subspecies N. marginatus picturatus Hoedeman, 1954 in having 19-22 scales in the lateral scale series instead of only 17-19. The new subspecies can be distinguished from N. marginatus marginatus known up to now by up to 2 teeth on each maxillary bone. Tricuspid teeth with the median cusp longest predominate teeth with more cusps. Furthermore, adult males are distinguished by a broad red area between the primary and secondary horizontal stripe extending from the tip of the snout to the base of the caudal fin, including the upper half of the iris. All of the three dark horizontal stripes are strong and distinctive. The primary horizontal stripe of adult males extends ventrally up to the posterior half of the anal fin base. There is no black margin along the anterior edge of the anal fin as in N. marginatus marginatus and in N. marginatus picturatus. In contrast, in N. marginatus mortenthaleri the last ray of the anal fin and therefore the posterior edge of the anal fin is black. The anterior part of the dorsal fin of the males is white near the base and red at the tip. All dorsal fin rays are partially black creating dark streaks on the fin. The last rays of the pelvic fin and the anal fin are also black creating dark borders at the respective parts of the fins.