Diagnosis of Arcturopsis Koehler, 1911 and redescription of A. giardi (Bonnier, 1896) (Crustacea, Isopoda, Arcturidae) Author King, Rachael A. Department of Zoology and Animal Ecology University College, Cork Lee Maltings, Prospect Row, Cork (Ireland) rachaelking @ crustacea. net Author Poore, Gary C. B. Museum Victoria, GPO Box 666 E, Melbourne, Vic. 3001 (Australia) gpoore @ museum. vic. gov. au. text Zoosystema 2001 23 3 467 477 journal article 10.5281/zenodo.5395729 1638-9387 5395729 Genus Arcturopsis Koehler, 1911 Arcturopsis Koehler, 1911: 8 . — Barnard 1920: 385- 386 . — Monod 1925: 72-73 . TYPE SPECIES . — Astacilla giardi Bonnier, 1896 (herein designated). SPECIES INCLUDED. — Arcturopsis giardi (Bonnier, 1896) ; Arcturopsis rudis Koehler, 1911 ; Arcturopsis senegalensis Koehler, 1911 . DIAGNOSIS Body cylindrical and geniculate. Lateral margins of head and pereonite 1 separated by incision. Antenna 2 slender, flagellum of 2 or 3 articles with row of spines medially and ending in a claw. Pereopod 1 with dactylus and unguis. Pereopods 2 to 4 cylindrical and slender with paired closely spaced long setae, flexed between the carpus and propodus, dactylus absent. Pereopods 5 to 7 with secondary unguis much smaller than the primary unguis and fused. Pereopods 5 to 7 progressively smaller. Pleotelson with small lateral wing. Oostegite 4 with posterior lobe. Male more elongate than female, especially pereonite 4; pereonite 3 possessing a midventral appendage with complex apex. Male pleopod 1 exopod laterally notched, with three long proximal setae on posterior face of exopod. Male pleopod 2 with appendix masculina elongate, exceeding endopod, with two apical flagellate appendices. REMARKS The key diagnostic characters that ensure the differentiation of Arcturopsis from other arcturid taxa are the extreme elongation of pereonite 4 in the male compared to the female and the presence of the midventral appendage on the male. The systematics of the genus has been confused by the transfer of species to other genera. Arcturopsis hirsutus Barnard, 1914 and its subspecies A. hirsutus subglaber Barnard, 1914 are junior synonyms of Astacilla corniger (Stebbing, 1873) (see Kensley 1984 ). Arcturopsis melitensis Koehler, 1911 is type and only species of Arctopsis Barnard, 1920 . Further confusion has been caused by the resemblance of female specimens of Arcturopsis to those of Arcturella Sars, 1897 . Monod (1925) attempt- ed to place Arcturopsis senegalensis in Arcturella based on observations on a single ovigerous female specimen. Believing that Koehler (1911) had included two separate species in his description of Arcturopsis rudis , Monod proposed that the females and some males belonged to a new species which he described as Arcturella dollfusi . Only the copulatory males with fully formed midventral appendages were retained in Arcturopsis rudis . The males described by Monod (1925) as Arcturella dollfusi are probably juvenile specimens of Arcturopsis giardi in which the midventral appendage is not fully formed. Arcturella dollfusi is therefore a junior synonym of Arcturopsis rudis . KEY TO SPECIES OF ARCTUROPSIS KOEHLER, 1911 1. Female pereonite 4 with distinct dorsal paired horns and lateral tuberculation; body of male and female heavily tuberculate ........................................................ A. rudis