Reference 18462

Two little-known Red Sea species in the amphipod genus Quadrimaera (Gammaridea, Melitidae) are redescribed: Q. schellenbergi (Ruffo, 1938) and Q. massavensis (Kossmann, 1880). The first one, endemic to the Red Sea, is primarily characterized by the presence of a row of very long setae on the hind margin of the basis of peraeopods 5-7. Q. massavensis was originally described by Kossmann (1880), who did not stress any distinguishing characters; the species was therefore for a long time considered a junior synonym of Q. inaequipes (A. Costa, 1851). Here it is shown that Q. massavensis is a valid species, clearly different from Q. inaequipes: the main diagnostic character is the presence of three long setae on the hind margin of the propodus of peraeopods 6-7. Q. massavensis is very similar to Q. pieteri Krapp-Schickel & Ruffo, 2000, from the Lesser Antilles, but the two species come from geographically very distant areas, making a synonymy little probable. Two new Quadrimaera species are described from the Indian Ocean: Quadrimaera franzi is a small Indonesian species, with a characteristic shape of the propodus of Gn 2, while Q. santiniae, from Amsterdam Island, is a robust species, with a length up to 9 mm, which shows a reverse sexual dimorphism of the propodus of gnathopod 2, contrary to what is the case in most Quadrimaera species. Quadrimaera santiniae is the most southern species of the genus, which otherwise has an wide distribution in the tropical Indo-Pacific and Atlantic Oceans as well as the Mediterranean Sea. Key words: Quadrimaera schellenbergi and Q. massavensis redescribed, Quadrimaera franzi and Q. santiniae new species. Red Sea. Indian Ocean.