Abstract
The genus Oxidus Cook, 1911 is revised to contain five species, O. avia (Verhoeff, 1937), O. gigas (Attems, 1953), O. gracilis (C.L. Koch, 1847), O. riukiaria (Verhoeff, 1940), and “species inquirenda” O. obtusus (Takakuwa, 1942). A cosmopolitan species, O. gracilis, is widely found in temperate and sub-tropical regions over the world, but other species have limited distribution in restricted regions, e.g., O. gigas in northern Vietnam, O. riukiaria and O. avia in the Ryukyu Islands (Japan). Four species, O. gracilis, O. riukiaria, O. avia and O. gigas, are confirmed as different from each other in gonopod characters, coloration and body size. The status of the last species, O. obtusus, is still doubtful and requires examination of further fresh material. The phylogenetic relationships among species of Oxidus is analyzed using two fragments of the mitochondrial genes COI (Cytochrome c Oxidase subunit I) and 16S rRNA. Three species of Oxidus are clearly separated from each other; O. gigas and O. gracilis form a monophyletic sister group with O. riukiaria. The genus Oxidus is also monophyletic and more closely related to the genus Tylopus Jeekel, 1968 than to the genera Sellanucheza Enghoff, Golovatch & Nguyen, 2004 or Kronopolites Attems, 1914. In addition, an identification key to species of Oxidus is provided.
Highlights
The genus Oxidus was proposed for the species Fontaria gracilis C.L. Koch, 1847 by Cook (1911)
Takakuwa (1942a, b) did not accept the genus Oxidus, and he reported ten species under the genus Orthomorpha from South Korea: Orthomorpha avia Verhoeff, 1937, O. circofera Verhoeff, 1931 (= Orthomorphella pekuensis according to Hoffman (1963)), O. circofera affinis Verhoeff, 1936 (= Orthomorphella pekuensis according to Hoffman (1963)), O. coarctata (De Sausure, 1860), O. gracilis, O. nordenskiöldi (Attems, 1909) (= Cawjeekelia nordenskioeldi according to Jeekel (1988)), O. pekuensis (Karsch, 1881) (= Orthomorphella pekuensis), O. riukiaria Verhoeff, 1940, O. cristata Takakuwa, 1942 (listed as species incertae sedis by Nguyen & Sierwald (2013)) and O. obtusus Takakuwa, 1942
All three species are distinctly separated from each other
Summary
The genus Oxidus was proposed for the species Fontaria gracilis C.L. Koch, 1847 by Cook (1911). On the contrary, Chamberlin (1945) recognised the genus Oxidus from Java (Indonesia) with eight species, Oxidus sequens Chamberlin, 1945, O. lamellifer Chamberlin, 1945, O. filarius (Attems, 1932), O. pygmaeus (Pocock, 1894), O. hydrobiologicus (Attems, 1927), O. annex Chamberlin, 1945, O. malabarus Chamberlin, 1945 and O. pangrangus Chamberlin, 1945 All those species were subsequently assigned to other genera (Jeekel 1963b; Nguyen & Sierwald 2013)
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