Omartacaridae is a small family currently recognised as including only two genera, Omartacarus and Maharashtracarus. They have a somewhat elongated body with a soft integument, contrasting with the more globular form of many other water mites. They are also distinguished by the arrangement of the coxae (the basal segments of the legs on the underside of the body) which are clustered together with the medial edges of the anterior pairs much longer than those of the posterior pairs (Walter et al. 2009) so the third pair of coxae are triangular in shape. As far as is known, omartacarids are restricted to interstitial habitats or the hyporheic zone of sediment beneath and alongside stream beds. I am unaware of any direct observations of omartacarid behaviour but they are presumably predators like other water mites. Most of the (rather limited) attention that has been given to omartacarids has focused on discussions of their distribution. Species of Omartacarus are found in South and southern North America, as well as in Australia. Maharashtracarus species are known from India and Costa Rica. It has been presumed that this reflects an ancestral Gondwanan distribution, spreading into North America from South America as the continents joined.
The larval stage of omartacarids is, to date, unknown. Larvae of other water mites live as parasites of water-associated insects such as midges and omartacarid larvae are presumably also parasitic. But in what capacity? Do mature omartacarids emerge from their subterranean habitats at some particular time of year in search of a host for their eggs? Do they somehow manage to find a host while remaining safely sequestered underground? The secret remains to be uncovered.
REFERENCE
Walter, D. E., E. E. Lindquist, I. M. Smith, D. R. Cook & G. W. Krantz. 2009. Order Trombidiformes. In: Krantz, G. W., & D. E. Walter (eds) A Manual of Acarology 3rd ed. pp. 233-420. Texas Tech University Press.
If the distribution is Gondwanan, those are some pretty old genera.
ReplyDeleteOld, yes, but not necessarily exceptionally so. Fossils of mites from early Cretaceous amber have been assigned to living genera.
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