A NEW SPECIES OF BATHYMEDON SARS, 1892 (AMPHIPODA, OEDICEROTIDAE) FROM THE WESTERN MEDITERRANEAN BATHYAL FLOOR

Bathymedon longirostris sp. nov. (Amphipoda: Oedicerotidae) from the w estern Mediterranean bathyal suprabenthos is described. It is characte rised by the well-developed rostrum; the discrete lateral lobe of head ; the elongation of the peduncle segment 3 of the first antenna; the v ery slender propodus of the second gnathopod, which attains maximum wi dth not at the palm angle, but at about midway along the palm margin, and by the relative length of the carpus of the foregoing limb, sub-eq ual to propodus. The discovery of a tiny remnant of the 2nd peduncle s egment of the first antenna in the new species is commented with regar d to the homologation of the peduncle segments in other members of the Family. The new taxon was captured below 593 m over muddy bottoms wit h pteropod shells and remains of planktonic foraminiferans. It was one of the most common amphipods in the lower slope (below similar to 100 0 m), whereas in the depth range comprised between 1250 and m it was t he second dominant species, representing 11.4 % of the total gammaride ans captured. The area studied harbours three additional congeneric sp ecies, although their populations are mainly concentrated in the upper and middle slope. Over the bottom, adult males of the new species app arently tend to occupy higher levels beyond the water-sediment interfa ce than the rest of demographic categories. The gut content of three i ndividuals revealed a bulk of calcified foraminiferans, a diet in cons onance with their massive mandibles. Juvenile individuals were more ab undant in winter, whereas adult individuals were clearly dominant in s ummer, thus suggesting the biological cycle of the species follows Som e type of periodicity.