Subterranean copepods (Crustacea, Copepoda) from the Pilbara region in Western Australia

WA Museum Records and Supplements | Updated 7 years ago

ABSTRACT – Subterranean copepods have been studied from 160 samples (from around 150 different localities) in the Pilbara region, collected by the Department of Conservation and Land Management, Western Australian Museum, mining companies and environmental consultants between 1997 and 2003. A rich and interesting copepod fauna was found in this arid area, comprising 41 species and subspecies classified into 24 genera, seven families and two orders (Cyclopoida and Harpacticoida). The following five genera are new to science: Australoeucyclops (Eucyclopinae), Orbuscyclops (Cyclopinae), Biameiropsis (Ameiridae), ArchinitocreIla (Ameiridae), and Abnitocrella (Ameiridae). Two new subgenera are also described: Rochacyclops (in the genus Halicyclops Norman, 1903) and Pilbaracyclops (in the genus Fierscyclops Karanovic, 2004). Only 11 species were previously known from the region, so an additional 30 species and subspecies of copepods are reported for the first time in the Pilbara in this monograph. Of them, 23 species and subspecies are described as new to science and ascribed to the following 15 genera: Halicyclops Norman, 1903 (one new species); Australoeucyclops gen. nov. (one species), Mesocyclops Sars, 1914 (one), Orbuscyclops gen. nov. (one), Diacyclops Kiefer, 1927 (four), Fierscyclops Karanovic, 2004 (two), Pseudectinosoma Kunz, 1935 (one), Schizopera Sars, 1905 (two), Parapseudoleptomesochra Lang, 1965 (one), Biameiropsis gen. nov. (one), ArchinitocreIla gen. nov. (one), AbnitocreIla gen. nov. (two), StygonitocreIla Reid, Hunt and Stanley, 2003 (three), Parastenocaris Kessler, 1913 (one), and ElaphoideIla Chappuis, 1929 (one new species). 

Keys to species worldwide are provided for the genera StygonitocreIla and Australoeucyclops, as well as for the Australian species of Halicyclops, Diacyclops, and Schizopera. Ameiropsis abbreviata Sars, 1911 is transferred into the newly established genus Biameiropsis, and the following four species are transferred into Australoeucyclops: Paracyclops eucyclopoides Kiefer, 1927, P. timmsi Kiefer, 1969, P. waiariki Lewis, 1974, and Eucyclops linderi Lindberg, 1948. Thermocyclops operculifer aberrans Lindberg, 1952 is elevated to specific status and recorded for the first time in Australia. PhyIlopodopsyIlus thiebaudi Petkovski, 1955 is also reported for the first time from Australia, as are the genera Pseudectinosoma and StygonitocreIla. The small cyclopoid genus Orbuscyclops is one of the exceptions in the family, showing that a reduction in body size is not necessarily closely followed by reductions in the segmentation of thoracic appendages. 

Of the 41 species and subspecies five have a cosmopolitan or almost cosmopolitan distribution, another five have a relatively wide distribution (three of them being Australian endemics), while 31 species and subspecies (76%) are endemic to the Pilbara region. A very long process of accumulation is likely to be one of the main reasons for such a rich fauna of subterranean copepods, as this part of Australia has been emergent, and hence a freshwater system, since the Precambrian. Representatives of the genera AIlocyclops Kiefer, 1931 and Parastenocaris may have invaded the subterranean waters of the Pilbara as early as the Jurassic, because these cosmopolitan genera have no marine relatives and no modern pathways between different continents, making it likely their present distribution is the result of continental drift. Although the majority of species from the Pilbara have a clear freshwater origin, no less than 16 species (39%) are marine derived, with their close relatives still flourishing in the marine environment. Some of them are quite recent colonisers, like the representatives of the genera Halicyclops, Schizopera, and PhyIlopodopsyIlus T. Scott, 1906. The Tethyan connection is clearly recognisable for many taxa and the characters of the first Australian representative of the genus Pseudectinosoma strongly suggests a Tethyan origin of this genus as well. A prominent zoogeographical feature of the Pilbara copepods with a freshwater origin is the Eastern Gondwana connection. 

Results of this survey are compared with those from the neighbouring Murchison region and some striking differences are revealed. Not a single species endemic to the Murchison was found in the Pilbara and those that occur in both regions are Widespread Australian or cosmopolitan species. There are also surprising differences in the copepod genera of the Pilbara and Murchison and similar differences were also observed and reported in fauna other than copepods. The only real connection between these two neighbouring Western Australian regions seems to be the genus Schizopera. A "pulsating desert hypothesis" has been tentatively proposed, that may account for some of the observed differences between the Pilbara and Murchison stygofaunas. During the past episodes of very severe aridity in Australia the real desert would spread westwards from the central part of the continent, perhaps wiping out most of the stygofauna and forcing the rest to retreat, first towards the coast and then either northwards or southwards of the Tropic of Capricorn. It is noted that the diversity of the three main freshwater harpacticoid families is quite different in Australian subterranean waters from elsewhere. This is explained as a reflection of a different colonisation history of the subterranean freshwater habitats in parts of the former Gondwana and in the Northern Hemisphere.