Tegnacus, Pye, Daniel R. L., 2012

Pye, Daniel R. L., 2012, New eriophyoid mites (Acari: Prostigmata: Eriophyoidea) in Britain: one new genus, four new species, 19 new records and two incursions, Zootaxa 3578, pp. 43-68 : 54-55

Tegnacus n. gen.

Description. Gnathosoma small in comparison to body with a short form oral stylet. Body fusiform, separated into large plate-like dorsal annuli which project slightly at lateral margins with small rounded lateral lobes, and with a broad and raised dorsal median ridge extending to posterior of opisthosoma, with narrow microtuberculate ventral annuli. First dorsal annulus behind prodorsal shield short, half as long as following annuli. Prodorsal shield with broad rounded frontal lobe over gnathosomal base. A transverse medially acuminate ridge forming a large hornlike process between frontal lobe and gnathosoma. Gnathosoma with setae ep and d present, simple, with setae v present and represented by a tiny spur. Scapular setae ahead of rear shield margin, on plicate tubercles directing setae centrad and upward. Internal genital apodeme extending forward, of normal length, not appressed to coxae. Dorsal opisthosomal setae c1 absent, ventral opisthosoma with setae c2, d, e and f present, posterior anal region with setae h1 and h2 present. Coxae with setae 1a, 1b and 2a present. Genital setae 3a present. Legs with all usual segments; leg I with seta bv, l ʺ, l ʹ, ft ʹ, ft ʺ and u ʹ present; leg II with seta bv, ft ʹ, ft ʺ and u ʹ present, seta l ʹ and seta l ʺ absent. Empodia simple, undivided.

Type species. Tegnacus unicornutus n. sp.

Classification. Following the classification by Amrine et al. (2003), Tegnacus fits into the family Eriophyidae , sub family Phyllocoptinae , tribe Tegonotini .

Etymology. The generic name, Tegnacus (masculine), is a contraction of the Latin ' tegumen ' or ' tegmentum ', meaning skin/cover/protection, and ' acarus ', meaning mite, which relates to the strong plate like annuli and resembling an 'armoured' mite.

Differential diagnosis. Following the classification by Amrine et al. (2003), Tegnacus is hereby placed into the family Eriophyidae , subfamily Phyllocoptinae , tribe Tegonotini due to the small rounded lateral lobes on the dorsal annuli at lateral margin, and is most closely related to the genus Tegonotus Nalepa 1890 . As shared with Tegnacus , the following six species currently assigned to Tegonotus were described or depicted as having seta l" absent from the genu on leg II: Tegonotus bassius Das & Chakrabarti 1982 , from Madhuca sp. ( Sapotaceae ) [originally listed as Bassia sp. ( Amrine & Stasny 1994)], India; Tegonotus eupators Huang 2001 , from Eupatorium formosanum Hayata (Asteraceae) , China (n.b. the original drawings show seta l" absent on genu II, but this was not mentioned in the written description); Tegonotus litseae Ghosh & Chakrabarti 1989 , from Litsea sp. ( Lauraceae ), India; Tegonotus marinalni ( Keifer 1939a) , from Alnus rubra Bong. (Betulaceae) , California, USA; Tegonotus simus ( Keifer 1940b) , from Alnus incana ssp. rugosa (Du Roi) Clausen ( Betulaceae ), Georgia, North Carolina, USA; and Tegonotus uranomus ( Keifer 1962a) , from Betula lenta L. ( Betulaceae ), Skyland, Virginia, USA (n.b. the original drawings show seta l" absent on genu II, but this was not mentioned in the written description). Incidentally, T. litseae , along with Tegonotus schleicherae Ghosh & Chakrabarti 1989 (seta l" present on genu II), from Schleichera oleosa (Lour.) Merr. (Sapindaceae) , could be congeneric with Neoshevtchenkella Kuang & Zhuo 1989 and Shevtchenkella Bagdasarian 1978 respectively as both were described as having the sc tubercles situated at the posterior of the prodorsal shield, directing the sc setae caudad.

Tegnacus clearly differs from these taxa, most strikingly, by having a transverse medially acuminate ridge forming a horn-like projection between the prodorsal shield lobe and the base of the palps, and by having the first dorsal annulus short [conventionally described as 'narrow' ( Amrine et al. 2003)]. When examining the original drawings of Tegonotus marinalni , what appears to be a slight projection on the underside of the prodorsal shield lobe was depicted. However, this appears to be an extension of the lobe. Specimens of T. marinalni need to be found and thoroughly examined to determine the nature of this projection as the feature was not mentioned in the original written description. Tegnacus also has some similarities to the genus Neoshevtchenkella , by having seta l ʺ absent from the genu on leg II. Neoshevtchenkella was described as having a pointed projection on the underside of the prodorsal shield lobe but this appears to be an extension of the lobe and directs down, whereas for Tegnacus the projection is separate from the lobe and directs forward. Neoshevtchenkella also differs from Tegnacus by having the sc tubercles on the rear shield margin, directing the sc setae backwards, and by having all the dorsal annuli equal in size.

Discussion. The suite of characters used to differentiate Tegnacus appear to be significant at the generic level ( Lindquist & Amrine 1996) but, like some other taxa in the Eriophyoidea , the generic concepts and separation of many taxa assigned to the tribe Tegonotini are thought to be weak and not based on natural groupings ( Lindquist & Amrine 1996). The aforementioned species currently assigned to Tegonotus need to be found and carefully examined to confirm the absence of seta l ʺ on genu II. In addition, the significance and uniqueness of the horn-like projection at the supraspecific level needs to be assessed when further taxa in this group of eriophyoid mites are described and their phylogenetic relationships are better understood.