Revision of the oribatid mite genus Austronothrus Hammer (Acari:Oribatida):sexual dimorphism and a re-evaluation of the phylogenetic relationships of the family Crotoniidae

Abstract

The Gondwanan relict oribatid mite family Crotoniidae contains the genera Austronothrus Hammer, 1966, Crotonia Thorell, 1876 and Holonothrus Wallwork, 1963. This family is of considerable interest biogeographically and also because the members of the family may have re-evolved sexuality from thelytokous parthenogenetic ancestors. Crotonia and Holonothrus are speciose and widely distributed whereas Austronothrus is obscure, hitherto monospecific and known only from New Zealand. We revise Austronothrus and compare it with its better-known congeners. Two new species of Austronothrus are described from New Zealand, namely A. clarki, sp. nov., and A. flagellatus, sp. nov. The only previously known species, Austronothrus curviseta Hammer, 1966, is redescribed and the genus is redefined. The presence of male specimens of all species confirmed Austronothrus as a sexual genus, like its congeners. Secondary sexual characteristics within Austronothrus and Crotonia include significant differences in body size and proportion, as well as the lengths and shapes of various setae, predominantly those of the notogastral region. Because these characters are frequently used by taxonomists to separate and define species within the Crotoniidae, it is important that the sex of adult specimens be determined to avoid describing conspecific males and females as separate species. A phylogenetic analysis based on morphological characters shows the crotoniid genera nested within the Camisiidae, with Camisia von Heyden, 1826 basal to the crotoniid clade of Austronothrus, Holonothrus and Crotonia, and with a clade of Platynothrus Berlese, 1913, Heminothrus Berlese, 1913 and Paracamisia Olszanowski & Norton, 2002 (Camisiidae) forming the sister clade of Camisia + Crotoniidae. Thus, Camisiidae is paraphyletic with respect to Crotoniidae. The family Crotoniidae is revised in light of the cladistic analysis, and relegated to subfamily rank. Three subfamilies are defined within the Camisiidae : Crotoniinae (containing Crotonia, Austronothrus and Holonothrus), Camisiinae (containing Camisia) and Heminothridae, subfam. nov. (containing Heminothrus, Platynothrus and Neonothrus Forsslund, 1955). Nothrus maximus Trägårdh, 1901 belongs to the genus Platynothrus and is recombined.