OMANOHYDRACARINAE, Gerecke, 2004

Gerecke, Reinhard, 2004, Water mites from spring- and ground-water habitats in the Sultanate of Oman, Journal of Natural History 38 (22), pp. 2833-2849 : 2837-2838

Subfamily OMANOHYDRACARINAE nov. subfam.

Diagnosis. Characters of the family Unionicolidae , such as absence of glandularia from Cx-3/4, posterior margin of coxae with projecting apodemes; IV-L insertions associated with strong, laterally directed projections; P-4 with a peglike seta in distal position; legs with heavy, movable setae inserting between paired dents.

Idiosoma with entire dorsal and ventral shields separated by a narrow stripe of papillate, membranous dorsal furrow; median eye not visible, lateral eyes strongly reduced, probably represented by pairs of minute lenses associated with the anterior margin of the ventral shield laterally from the anterior glandularia. All glandular openings incorporated into the idiosoma shields, only pairs of slit organs free in the membrane of the furrow; surface of ventral shield with honeycomb-like porosity, in tangential view visible as a papillate structure; all suture lines confining the merged coxae well visible; distal edges of Cx-1–3 with paired extensions not curved or hook-like, Cx-4 with an unpaired, laterally directed extension covering the leg insertion; posterior margin of Cx-1 z 2 with well-developed, but not caudally extended, apodemes placed on the level of the insertions of III-L; suture line separating Cx-3/4 well developed, nearly reaching the medial margin of the coxal plate; caudal apodemes of Cx-4 well developed, extending from a triangular projection of the posterior coxal margin; legs without swimming hairs, bearing simple claws, without clawlets or blades, III- and IV-L exhibiting strong sexual dimorphism. One pair of glands between coxal and genital fields; genital field completely incorporated into the ventral shield, in a bay formed by the concave mediocaudal margins of Cx-4; gonopore inversely drop-shaped in males, but with maximum width in the centre in females, flanked by genital hairs in low number, numerous acetabula (in males about 20, in females about 12) scattered between its anterior part and the coxal margins; excretory pore imbedded into the posterior margin of the ventral shield. Genital skeleton elongated, but conventional in shape, with poorly developed keels; dorsal shield surface with honeycomb-like porosity, at regular distance interrupted by circular fields of finely papillate membranous integument. These fields in the lateral parts of the shield arranged more regularly, recalling the pattern of muscle attachments in plesiotypic water mite families, in the centre irregularly and asymmetrically.

Gnathosoma and mouthparts short and robust, posterior margin of gnathosoma without anchoral process; palps exhibiting strong sexual dimorphism; in both sexes P-4 with a pointed dorsodistal extension and variously shaped ventral projections.

Type genus. Omanohydracarus gen. nov.

Discussion. ‘There is so much variation in most characteristics, even within a genus, that it is difficult to write an all inclusive family diagnosis. Yet the family seems to be a natural group. Although many species have become divergent in one or possibly two characteristics, the remaining characters show their affinities with the more typical members of the family’ ( Cook, 1974). This new taxon brings a new facet into this taxonomical mosaic because it merges character states typical for unionicolid mites with character states so far known only in members of the Pionidae .

The combination of unionicolid characters in Omanohydracarus , suggesting classification of the genus within this family, embraces the well-developed, laterally directed projections of Cx-4 covering the insertions of IV-L, and the absence of clawlets and claw blades from leg claws. However, the character set defining Omanohydracarus enlarges considerably the morphological diversity within this family. From various points of view, Omanohydracarus is intermediate between Pionidae and Unionicolidae : pionid-like features are (1) the short, not caudally extended apodemes of Cx-1; (2) the triangular extensions of the caudal margin of Cx-4 at the base of the posterior apodemes. With regard to the peg-like seta of P-4, there is a sexual dimorphism with a pionid-like distal position in males, and a unionicolid-like ventrodistal position in females (see below).

Within Unionicolidae , Omanohydracarus displays a considerable similarity to Pollicipalpus , the only genus of Pollicipalpinae, in the shape of P-4 (with pointed distal extensions covering the base of P-5), and the absence of swimming hairs on legs. Species of Pollicipalpus are also similar in the presence of dorsal and ventral shields, but differ from Omanohydracarus in important characters such as the presence of sharp-pointed distal projections on Cx-2/3 and of clawlets on leg claws, the position of the genital field far distant from the posterior margin of Cx-4 and the dorsal position of the excretory pore.