Messoracaridae Kethley, 1977

Kontschán, Jenő & Seeman, Owen D., 2012, A new species of Messoracarus (Acari: Mesostigmata: Aenictequoidea: Messoracaridae) from Laos, Zootaxa 3527, pp. 55-62 : 56

Family Messoracaridae Kethley, 1977

Messoracaridae, Kethley, 1977: 135 .

Messoracaridae .— Lindquist et al., 2009: 129, 159.

Diagnosis (based partially on Kethley 1977, Kim 2008). Dorsum convex, margins circular, with 40–90 robust marginal setae. Tritosternal laciniae fused completely. Sternal shield fragmented into five plates: paired presternal plates, bearing setae st1; anteromedial subtriangular plate; medial rectangular plate bearing setae st2; and a posterior sternal plate bearing st3. Latigynal shields rectangular or subrectangular, mesal margins parallel. Mesogynal shield obscured by latigynal shields or absent. Gnathotectum with serrate margin. Legs short, leg I shorter than half body length, claws absent.

Type genus. Messoracarus Silvestri, 1912 , designated by Kethley (1977).

Remarks. All messoracarid mites are medium-sized mites, ranging between 450 and 780 μm in length. In comparison, the Aenictequidae , Euphysalozerconidae and Ptochacaridae are all large mites (> 1 mm length). The most striking feature of the Messoracaridae is the large rectangular latigynal shields. However, messoracarid mites also have a unique sternal shield arrangement with five shields, of which the posterior fragment bearing setae st3 is unusual. This fragment resembles the sternogynum (which bears the lyrifissures stp3 only) or pseudosternogynum (which is bare) of some other trigynaspid mites ( Kim 2004). The two genera in the family, Leptantennus and Messoracarus , are separated by one character. In Leptantennus the mesogynal shield is weakly sclerotised, but in Messoracarus it is absent or hidden by the two latigynal shields.

Biology. Leptantennus pendulipes and Messoracarus mirandus were collected from ants. Hosts for the other two species are unknown. Silvestri (1912) found specimens of M. mirandus in ant nests and observed several mites on the lateral part of the head of ants, posteriorly to the eyes (see Silvestri 1912, Fig. IV).