Mezhov B.V. 2004. New species of the genus Macrostylis G.O. Sars, 1864 (Crustacea: Isopoda: Macrostylidae) from the abyssal and ultraabyssal zones of the Indian Ocean // Arthropoda Selecta. Vol.12 (for 2003). No.3–4: 159–165 [in English].

Zoological Museum of the Moscow State University, Bolshaya Nikitskaya Str. 6, Moscow 125009 Russia.

ABSTRACT. The descriptions of four new species from the genus Macrostylis G.O. Sars, 1864 (collections R/V “Vityaz” from the eastern part of the Indian Ocean) are given. Macrostylis pectorosa sp.n. (29°43’S, 89°53’E; 2807 m) differs from the closely related species by the following characters: the considerably smaller sizes, single pointless sternal spine in the pereonal anterior division, proportions of the antenna I and structure of the pereopod III — from  M. caribbicus Menzies, 1962; the absence of pits on tergites, morphology of the antenna I, configuration of the pereopod III ischiopodite and structure of operculum — from M. foveata Mezhov, 2000; the macrosculptural peculiarities of tergite IV, morphology of the cutting margin of mandible, comparatively narrower epipodite and palp of maxillipede, relatively elongated pereopods — from M. squalida Mezhov, 2000. M. pumicosa sp.n. (4°59¢N, 90°47.5¢E; 2917 m) differs from the related M. rectangulata Mezhov, 1989 by the cavernousity of dorsal covers and absence of their setation, configuration of the pereonal anterior division and correlation of the tergites composing it, configuration of pleotelson, morphology of the pereopod III ischiopodite and meropodite and angularly tapered distal end of the second pleopod. M. diatona sp.n. differs from the related M. hadalis Wolff, 1956 by the shortened pleotelson with the larger mediodistal lobe, the narrower operculum with smaller (half?) number of bristles on the distal margin, the clavate distal parts of the pleopod I hyaline processes; from the related M. longiuscula Mezhov, 1981 new species differs by the configuration of pleotelson, morphological peculiarities of the pereopod III ischiopodite and meropodite, the visible less curved hyaline processes of pleopod I. M. fragosa sp.n. differs from the related M. reticulata Birstein, 1963 by the twin pits on tergites IV–VII, the rounded lateral surfaces of pleotelson and relatively broadened operculum with the distinctly truncated narrow distal margin.

KEY WORDS: Isopoda, Macrostylis, new species, abyssal zone, ultraabyssal zone, Indian Ocean.

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