South American Mites

Diagnostic views of Charassobates cavernosus (clockwise from left: dorsum; prodorsum with covering lamellae removed; venter) from Schuster (1969).

For this week's random taxon, I drew the oribatid mite family Charassobatidae. This has proved to be something of a challenge: info on the charassobatids seems a little hard to come by. It doesn't help that the 'Charassobatidae' has haemorrhaged taxa somewhat. Balogh & Balogh (1992), in their invaluable (if not entirely unproblematic) identification guide to oribatids, listed three genera in the Charassobatidae: Charassobates, Topalia and Ametroproctus. The main reason for associating these genera appears to have been the presence of massively expanded lamellae on the prodorsum (the 'head' part of the mite). However, Behan-Pelletier (1988), in transferring Ametroproctus to the family Cymbaeremaeidae, argued that this feature had probably arisen convergently as similar large lamellae are known from other oribatid families. Topalia has also since been removed from Charassobatidae, which is now redundant with Charassobates. Norton & Behan-Pelletier (2009) placed Charassobates in the superfamily Licneremaeoidea, but the monophyly of that group has been questioned (Schäffer et al. 2010).

Charassobates is a strictly South American group of mites (with an outlying species in the Galapagos). They have pelopsiform (very long and slender) chelicerae, possibly indicating a liquid diet, that are also somewhat unusual among oribatids in lacking an articulation between the chelicerae and the underside of the 'head'. Some species, such as the type Charassobates cavernosus, also possess deep fossae on the dorsal surface of the main body. The nymphs are wrinkly (unlike humans, some oribatids become less wrinkly as they get older) and apheredermous (i.e. they do not carry the shed skins of former instars as protective scalps) according to Norton & Behan-Pelletier (2009) and Behan-Pelletier & Walter (2007), indicating that their description as eupheredermous (carrying scalps) by Behan-Pelletier (1988) was probably an error.

REFERENCES

Balogh, J., & P. Balogh. 1992. The Oribatid Mites Genera of the World. 2 vols. Hungarian Natural History Museum.

Behan-Pelletier, V. M. 1988. Systematic relationships of Ametroproctus, with modified definition of Cymbaeremaeidae (Acari: Oribatida). In: Channabasavanna, G. P., & C. A. Viraktamath (eds) Progress in Acarology vol. 1 pp. 301-308. E. J. Brill: Leiden.

Behan-Pelletier, V. M., & D. E. Walter. 2007. Phylleremus n. gen., from leaves of deciduous trees in eastern Australia (Oribatida: Licneremaeoidea). Zootaxa 1386: 1-17.

Norton, R. A., & V. M. Behan-Pelletier. 2009. Suborder Oribatida. In: Krantz, G. W., & D. E. Walter (eds) A Manual of Acarology pp. 430-564. Texas Tech University Press.

Schäffer, S., S. Koblmüller, T. Pfingstl, C. Sturmbauer & G. Krisper. 2010. Ancestral state reconstruction reveals multiple independent evolution of diagnostic morphological characters in the “Higher Oribatida” (Acari), conflicting with current classification schemes. BMC Evolutionary Biology 10: 246.

Schuster, R. 1969. Die terrestrische Milbenfauna Südamerikas in zoogeographischer Sicht. In: Fittkau, E. J. (ed.) Biogeography and Ecology in South America vol. 2 pp. 741-763. Dr W. Junk N. V.: The Hague.