Nosybelba: A Uniquely Madagascan Mite

Dorsal and ventral views of the main body of Nosybelba oppiana, from Mahunka (1994).

Why yes, it's another random oribatid! Nosybelba oppiana was described from Madagascar by Sándor Mahunka in 1994; Mahunka regarded it as distinct enough from other oribatids that he placed it in its own monospecific family. To date, the original description appears to be the sum total of our knowledge of Nosybelba oppiana. Subías et al. (2012) transferred it to a separate subfamily within the larger family Oppiidae, and transferred a second Madagascan species 'Oppia spinipes' Balogh 1964 to Nosybelba, but this was in the context of a species checklist only without supporting discussion (also, the name Oppia spinipes was used for an oribatid species by Banks in 1906, so whatever the status of Balogh's species it needs a new name).

Leg I of Nosybelba oppiana, from Mahunka (1994). Femur and genu of the right, tibia and tarsus on the left.

So what can we tell about Nosybelba from its description? One of the first things that attracts attention is that it has rather weird legs. The tarsi (the terminal segments) of the legs are really short, shorter on all legs than the adjoining tibia. On the first pair of legs, the tarsus is also compressed longitudinally, and a dorsal process on the tibia (that bears a large sensory seta) overhangs the tarsus. To my admittedly uneducated eyes, the overall structure does not give an impression of mobility. I'm guessing that Nosybelba is not the most agile of oribatids. At the end of each leg is a single large claw; as mentioned in a previous post, the number of claws on an oribatid's legs tends to correlate with habitat, with single claws suggesting a terrestrial lifestyle.

Lateral view of front end of Nosybelba oppiana (minus legs), from Mahunka (1994).

Another noteworthy feature of Nosybelba can be found in its mouthparts. The mentum, the 'under-head' shelf that underlies the chelicerae, does not have a basal articulation, so the chelicerae are limited in their range of movement. The chelicerae themselves do not have any teeth, so Nosybelba is not feeding on anything that requires a great deal of processing before swallowing. In another oribatid family, the Suctobelbidae, similar chelicerae are related to a diet of plant matter that is in an advanced state of decay; Nosybelba is presumably also a connoiseur of the rotten and the liquefied.

REFERENCES

Banks, N. 1906. New Oribatidae from the United States. Proceedings of the Academy of Natural Sciences of Philadelphia 58 (3): 490-500.

Mahunka, S. 1994. Oribatids from Madagascar II. (Acari: Oribatida). Revue Suisse de Zoologie 101 (1): 47-88.

Subías, L S., U. Ya. Shtanchaeva & A. Arillo. 2012. Listado de los ácaros oribátidos (Acariformes, Oribatida) de las diferentes regiones biogeográficas del mundo. Monografías electrónicas S.E.A. 4.