Dorsum of Metarhaucus lojanus, from Roewer (1912).

Belongs within: Cosmetidae.

Metarhaucus is a poorly defined genus of harvestmen found in Central and South America.

On Metarhaucus
Published 7 September 2010

This is a bit of a hard one to recognise. The most distinctive feature of the Cosmetidae, the harvestman family to which this animal belongs, is their laterally flattened pedipalps, not shown in the picture above. Without that, you would have had to combine vaguer features such as the overall shape of the body, the lack of spines on the eyemound (most related families have at least small spines) and how the divisions between the regions of the dorsal shield are less sharply incised than in other families.

Metarhaucus is a genus of eleven species of cosmetid, mostly found in Colombia, Ecuador and Peru (a single species has been described from Costa Rica; Kury, 2003). The genus has not been revised since the days of Roewer so it suffers the usual problems with Roewer’s usage of genera based on characters that may turn out to be unreliable with further study. Roewer’s (1912) defining characters for Metarhaucus were the presence of six pseudosegments in tarsus I, more than six pseudosegments in tarsus III, third and fourth legs much thicker than the front two pairs and the presence of a median pair of tubercles on the second and fourth areas of the dorsal shield. The South American Cosmetidae are currently under review by researchers in Brazil; time will tell whether Metarhaucus survives their scrutiny.

Systematics of Metarhaucus

Characters (from Roewer 1923): Sturdy animals with strong (especially third and fourth) legs. Areas 1, 2 and 4 each with one median tubercle pair; area 3 with one median spine pair; area 5 and free tergites 1–3 unarmed. Second cheliceral segment much thicker in male than in female and distinctly rising above the first segment. Legs in both sexes with basal segment of legs III and especially IV much thicker and stronger than that of legs I and II; telotarsus II three-segmented; telotarsus I six-segmented; tarsi II–IV each more than six segments, variable.

<==Metarhaucus Pickard-Cambridge 1905 [incl. Erginus Simon 1879 non Jeffreys 1877]K03
    |--*M. fuscus Pickard-Cambridge 1905 [=Erginus fuscus]K03
    |--M. conspicuus Roewer 1927K03
    |--M. devillei (Simon 1879) [=*Erginus devillei, Rhaucus devillei]K03
    |--M. lojanus (Roewer 1912) [=Erginus lojanus]K03
    |--M. ohausi (Roewer 1912) [=Erginus ohausi]K03
    |--M. reimoseri Roewer 1933K03
    |--M. reticulatus Roewer 1912 [=Erginus reticulatus]K03
    |--M. serrifemur Roewer 1927K03
    |--M. trilineatus (Sørensen 1932) [=Rhaucus trilineatus]K03
    |--M. unicolor Roewer 1957K03
    `--M. variatus (Roewer 1912) [=Erginus variatus]K03

*Type species of generic name indicated


[K03] Kury, A. B. 2003. Annotated catalogue of the Laniatores of the New World (Arachnida, Opiliones). Revista Ibérica de Aracnología, volumen especial monográfico 1: 1–337.

Roewer, C. F. 1912. Die Familie der Cosmetiden der Opiliones—Laniatores. Archiv für Naturgeschichte, Abteilung A 10: 1–122, pls 1–2.

Roewer, C.-F. 1923. Die Weberknechte der Erde: Systematische Bearbeitung der bisher bekannnten Opiliones. Gustav Fischer: Jena.

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