Pionacercopsis Viets, 1926

Smith, Ian M., Cook, David R. & Gerecke, Reinhard, 2015, Revision of the status of some genus-level water mite taxa in the families Pionidae Thor, 1900, Aturidae Thor, 1900, and Nudomideopsidae Smith, 1990 (Acari: Hydrachnidiae), Zootaxa 3919 (1), pp. 111-156 : 117-118

Genus Pionacercopsis Viets, 1926

Pionacercus (Pionacercopsis) : Cook, 1974a, pp. 285–286, figs. 1204, 1205. Pionacercus (in part): Smith, 1976, pp. 44–46, 79–81.

Pionacercopsis: Gerecke, 2014 , p. 59, fig. 1.

Diagnosis. Larva: Unknown.

Adults (modified from Cook 1974a): Character states of subfamily Foreliinae. Idiosoma with dorsal integument mostly soft and bearing only tiny platelets associated with glandularia and idiosomal setae. Venter with coxal plates and genital field incorporated into a ventral shield in males, but surrounded by soft integument bearing only tiny sclerites associated with glandularia and idiosomal setae in females. Fourth coxal plate with medial edge short but not reduced to angle in males, reduced to angle in females. Genital field with three pairs of relatively large acetabula borne on ventral shield flanking gonopore in males and on triangular acetabular plates flanking gonopore in females, extending laterally to but not beyond posterolateral angles of fourth coxal plates. Pedipalp segments long and slender and with tibia bearing two slender, sessile setae ventrally and a sessile, peg-like seta distomedially in males, and shorter and more stocky and with tibia bearing two slender setae on a small projection ventrally and a sessile, peg-like seta distomedially in females. Male third leg with tarsus bearing reduced claw sockets that are terminal in position and small but only slightly modified claws; fourth leg with genu short, slightly expanded, and bearing patches of thick, blade-like setae both at the base of and on a prominent distoventral projection, tibia relatively long and slender and bearing a row of swimming setae distodorsally, tarsus curved dorsally, bearing a patch of thick, peg-like setae only in region proximal to deepest part of curved portion, and bearing thick, highly modified claws.

Type species. Tiphys vatrax Koch.

Species included. Pionacercopsis vatrax (Koch) (northern Europe) (monobasic) but there is an undescribed species of Pionacercopsis from northern Canada in the Canadian National Collection of Insects and Arachnids.

Distribution. Holarctic (Europe, North America).

Discussion. Cook (1974a) treated Pionacercopsis as a subgenus of Pionacercus . Smith (1976) included the species of Pionacercopsis in his concept of Pionacercus without discussing subgenera. Gerecke (2014) proposed elevation of Pionacercopsis to full generic rank. We follow that treatment here based on the apomorphic condition of the distal segments of the fourth leg in males and the unique configuration of the genital field in both sexes. The modifications to the distal segments of the fourth leg of males are similar to those found in males of the genus Madawaska (see above) suggesting that members of the two genera may be closely related. The phylogenetic affinities of Pionacercopsis with Madawaska and other Foreliinae will be better understood when adults and larvae of additional species are described.