Pseudofeltria (Acariformes: Pionidae) in Europe: Three previously described taxa, a species new to science from the Northern Apennines, and a redefinition of Foreliinae

The morphological variability of Pseudofeltria scourfieldi Soar, 1904, a water mite species known from scattered sites in Central and Northern Europe, is documented on the base of populations from the Bavarian Alps and bibliographic data; its diagnostic characters are discussed in comparison with P. quadriscutata Biesiadka, 1971 from Western Beskides (Poland) and P. aemiliana n. sp. from mountain springs in the Region of Emilia Romagna (Italy). Pseudofeltria vanrensburgi Bader, 1974 (Switzerland) is a junior synonym of Forelia variegator (Koch, 1837). A new diagnosis of the subfamily Foreliinae is given and discussed, including species of the genera Pionacercopsis (former subgenus of Pionacercus, here elevated to the genus rank) and Pionacercus.


INTRODUCTION
The genus Pseudofeltria was first described from England, with P. scourfieldi Soar, 1904 as type species. A second species, P. scutigera Walter, 1922, detected in the Swiss Alps and in the following decades recorded from several parts of Central and Northern Europe, was recognized as a junior synonym of P. scourfieldi by Gledhill (1960). In the second half of the past century, six further representatives of the genus were described from Northern America (P. multipora Cook, 1955: Michigan;P. laversi Cook, 1974: Wyoming;P. jonfraseri Habeeb, 1977 andP. julia Habeeb, 1977: California) and Europe (P. quadriscutata Biesiadka, 1971: Poland, P. vanrensburgi Bader, 1994. As far as information on habitat preference is available, most Pseudofeltria species are bound to weakly seeping helocrenes which are often exposed to bright sunshine. Descriptions of the larval instar were published for P. multipora by Smith 1976 and P. scourfieldi by Martin (2000). Larvae of both species are abdominal parasites of Chironomid midges (Smith andOliver 1986, Martin 2000).
During research on the biological diversity in springs of the Northern Apennines, Cantonati et al. (MTSN) detected in 2011 two populations of a species new to science. A definition of its diagnostic features required a revision of the previously described European taxa. In addition, some thought on the diagnostic features of Pseudofeltria induced me to reconsider also the global systematics of Forelia-like genera and to modify the diagnosis of the subfamily Foreliinae such that the genus Pionacercus may be accommodated here as proposed as early as 1976 by Smith. The results of these studies are given in the present paper.

MATERIALS AND METHODS
Zoobenthos material was collected in the Berchtesgaden National Park during field work for the long term monitoring of spring habitats (Gerecke and Franz 2006) and in the Northern Apennines in the course of the EBERs project (Exploring the Biodiversity of Emilia Romagna springs, 2011-2013. Sorting of samples and species identification of water mites was done by the author. As far as necessary, specimens were dissected as described by Gerecke et al. (2007).

Family Pionidae, subfamily Foreliinae
Diagnosis -Integument of idiosoma from smooth to completely covered by dorsal and ventral shields, leaving only a narrow membranous dorsal furrow. Posteromedial apodemes of Cx-I varying from short to moderately long. Medial margins of Cx-IV often (in multiacetabulate species always) reduced to median angles. If medial margins of Cx-IV are developed, in females they form blunt or rounded, never sharp, posteromedial angles. Genital field occasionally with three, generally with numerous acetabula, in males along its whole anterior edge fused to Cx-IV. Posteromedial margin of gnathosoma with a short to moderately long anchoral process. P-4 with a peg-like distomedial seta. In males, IV-L-6 with a dorsal concavity flanked by two to numerous peglike setae, occasionally also IV-L-4 and III-L-6 modified for sperm transfer, but IV-L-5 simple.
Discussion -Separation of Tiphysinae from other pionids on the base of the presence of only three pairs of acetabula was never satisfactory -not only due to the presence, in the Nearctic, of a polyacetbulate Tiphys species, but mostly because the triacetabulate condition is a plesiomorphy (Cook 1974). In a cladistic analysis, Smith (1976) showed Pionacercus to be the outgroup of [Forelia and Pseudofeltria], but the necessary consequence, shifting the genus to Foreliinae, has not been taken so far. His interpretation is supported by the sexual modification of male legs for sperm transfer in representatives of all three genera: The deep dorsal incurvation of IV-L-6, flanked by peg-like setae (Figs. 1 D, 3 C-D, 4 A-D) is an obvious synapomorphy. As a consequence, the subfamily must be redefined as above, and we must assume that polyacetabulism evolved within this clade in parallel to Pioninae.

Genus Forelia Haller, 1882
Diagnosis -Secondary sclerotization on dorsal surface may be developed (from small platelets to a large shield) or not. Coxae, genital sclerites and excretory pore separated by membranous interspace in both sexes. Medial margins of Cx-IV reduced to median angles. Legs with swimming setae. Male III-L-6 differing in proportions and shape of claws from I-/II-L-6. Genital field with 7 to more than 50 pairs of acetabula.
Discussion -Species of the genus are characterized by the combination of: (1) presence of swimming setae, (2) a reduced medial margin of Cx-IV, (3) modified claws on male IV-L, and (3) the number of acetabula > three pairs.
Discussion -In the original description of Pseudofeltria vanrensburgi, Bader (1994) wondered about the presence of swimming setae in an interstitial-dwelling species and considered that type of leg setation as diagnostic in comparison with all other species of the genus. The fact that representatives of the sister taxon Forelia, all characterized by this type of leg setation, are generally found in standing waters only, probably was the reason for Bader not to consider the possibility of a Forelia-species appearing in an interstitial sample. The two specimens clearly represent Forelia variegator, not showing any remarkable morphological deviation from that widely distributed species. As F. variegator not rarely appears in pool areas of running waters, an occasional detection of drifting specimens in a stream sediment sample (the indication "COOK" on the label refers probably to the kick sampling method) is not surprising.

Genus Pionacercopsis K. Viets, 1926
Diagnosis (after Cook 1974, modified) -Idiosoma soft in female, but with dorsal and ventral shields in male. Coxal plates in four groups in female, but Cx-I+II medially fused and Cx-III+IV closely in touch in male. Cx-I+II with short posterior apodemes, Cx-IV medial margin well developed in male, in females medial margin of Cx-III+IV mostly formed by Cx-III. Genital field with three pairs of large acetabula; in females genital plates triangular, with strongly reduced sclerotized surface, mostly covered by acetabula and with concave medial and lateral margins between anterior and posterior acetabula. Males without petiole. P-4 mediodistally with small peg-like seta. Male IV-L exhibiting sexual dimorphism: IV-L-4 with a spur-like extension covered by numerous peg-like setae, IV-L-6, which is bowed with 7-8 peg-like setae on concave margin.
Discussion -Up to date, Pionacercopsis was ranked as a subgenus of Pionacercus. However, distinct character states (a long and slender palp and rather large, circular acetabula in both sexes, in males the development of a dorsodistal spur on IV-L-4, in females the reduction of the sclerotized genital plate surface around the acetabula) suggest to consider this taxon as a separate genus.

Genus Pionacercus Piersig, 1894
Diagnosis -Idiosoma soft in female, but with extensive sclerotizations in male, including dorsal and ventral shields. Medial margin of Cx-IV well developed in males, but more or less reduced in females.
In males, Cx-III+IV fused medially and with genital plate, occasionally also with Cx-I+II to a ventral shield; in females, coxal plates in four groups. Male IV-L-4 dorsodistally with a group of strong setae, but not forming a spur. IV-L-6 bowed, with 5-10 peg-like setae on concave margin. Genital field with three pairs of acetabula, in females triangular genital plates flanking membranous gonopore with acetabula covering only restricted parts of the plate, medial and lateral margins between anterior and posterior acetabula straight or bowed. Males without petiole. P-4 mediodistally with small peg-like seta.
Discussion -Material of three species of the genus was taken in study in order to document both, the distinctive character states for separating it from Pionacercopsis, and the synapomorphies with Pseudofeltria.

Genus Pseudofeltria Soar, 1904
Diagnosis -Secondary sclerotization extended dorsally (with several plates or one large shield, sexual dimorphism frequent) and ventrally (ventral shield including genital sclerites and excretory pore in males, occasionally also in females). Medial margins of Cx-IV reduced to median angles. Legs without swimming setae. III-L claws without sexual dimorphism, in shape similar to I-II-L claws. Male IV-L-5 dorsal and ventral margins distally diverging, with four to six large blade-like distoventral setae; IV-L-6 with large, unmodified claws and a strong dorsal concavity flanked by numerous peglike setae (long and densely arranged on the proximal margin, short and more distanced from each other on the distal margin). Genital field with 7-30 pairs of acetabula.
Discussion -Species of Pseudofeltria and Pionacercus agree, and differ from species of Forelia, in the plesiomorphic absence of a sexual dimorphism in III-L. They differ from Pionacercus and agree with Forelia in the apomorphic polyacetabulate condition of the genital field and differ from both genera in the absence of swimming setae and the presence of unmodified IV-L claws in males. Following a hypothesis of Cook (1974)  pairs of Ac, these often longish, maximum diameter of the largest 22 -30 µm. Male and female dorsum with one large shield including postocular setae at anterior margin, and posterolaterally two pairs of dorsoglandularia. P-4 with a pair of strong dorsal setae in distal third. Description: Both sexes -Colour yellow to brownish. Membranous parts of integument strongly striated, sclerites with a very fine porosity arranged in roundish or longish groups. Palp: P-1 with a stout dorsal seta, P-2 with 5 dorsal setae, ventral margin nearly straight, with a weakly developed projection in distal third; P-3 ventral margin concave, dorsal margin convex, one dorsomedial seta, a pair of stronger developed dorsodistal setae; P-4 robust, dorsally with three setae, one fine in centre, two strong in distal third, ventral margin with a pair of fine setae near a small pointed projection in distal third, distal margin with a strong, pointed peg seta. P-5 stout, with 4 strong claws.
Discussion -The idiosoma and palp measurements of the Bavarian populations lie within the size range given by Gledhill (1960) except for the, absolutely and relatively, slightly longer P-3. Furthermore, with an idiosoma length of 618 -636 µm, females from the English lake district are larger than both the holotype (560) and the Bavarian specimens, but Schwoerbel (1959) published intermediate size ranges (558 -625 µm) from females collected in Alsace (France). The holotype male of P. scutigera is minor in size than the minima calculated for populations from Bavaria (see above) and from the English Lake district (Gledhill 1960), but does not show remarkable differences in proportions. No data were previously published for single leg segments. The specimen from the Bulgarian Rila mountains agrees in number and shape of Ac, but differs in the presence of an additional small sclerite platelet in the posterior dorsal furrow.
Discussion -Pseudofeltria quadriscutata differs from the other European species in the high number of acetabula (following our experience a character state that should be similarly expressed also in the still unknown male). Females of the species are furthermore unique in the name giving presence of four dorsal plates and in the absence of strong dorsal setae on P-4. From the measurements published by Biesiadka (1971) results that the species is larger than the maxima measured for females of P. scourfieldi: Idiosoma length/width 700/570; coxal field length/width 400/433; length/height P-1, 54/54; P-2, 120/75; P-3, 59/59; P-4, 110/46; P-5, 43/19. In general palp proportions, with rather slender P-2-4, P. quadriscutata is similar to P. scourfieldi females, but it differs in a relatively longer P-2 (relative length 31 %, P-2/3 length ratio 2.0).