On the systematic of the water mite Hydryphantes prolongatus Thon , 1899 ( Acari , Hydrachnidia , Hydryphantidae )

The first description of larva and deutonymph, and redescription of female and male of the water mite Hydryphantes prolongatus Thon, 1899 are given. The proposal of Lundblad (1962), to synonymize H. prolongatus with H. ruber (Geer, 1778) is rejected.


Introduction
The water mite Hydryphantes prolongatus Thon, 1899 is widely distributed in Europe and known only from adults.Originally H. prolongatus was described as a form of H. ruber (Geer, 1778) and for a long time treated as a form or subspecies of this species (Thon 1899;Piersig 1897Piersig -1900;;Soar & Williamson 1925;K.Viets 1936K.Viets , 1956;;Sokolow 1940;Szalay 1964, K.O. Viets, 1978, 1987, etc).However, Lundblad (1962) proposed synonymization with H. ruber (Geer, 1778), followed by Di Sabatino et al. (2010).The aim of the paper is to discuss the taxonomic status of H. prolongatus, based on a morphological study of larvae, deutonymphs (both described for the first time) and adults.

Material and Methods
Specimens were collected by the author in temporary reservoirs of the European part of Russia.To obtain larvae, water mites were maintained in laboratory (room temperature, natural day-night conditions).Eggs and larvae obtained from females kept individually in glass or transparent plastic vessels of 10-15 mm diameter, and a height of 15 mm.

Research Article
tarsus) i.e.III-Leg-3 = genu of third leg; C1 -coxal seta located medially on coxa I, C2 -coxal seta located posterolaterally on coxa I, C4 -coxal seta located anteromedially on coxa III; e-eupathidium, ssolenidion, ac -acanthoid seta; I-Leg-6: de1 -distance between the anterior end of segment and eupathidium, ds1 -distance between the anterior end of segment and solenidion; II-Leg-6: de2 -distance between the anterior end of segment and eupathidium, ds2 -distance between the anterior end of segment and solenidion; L -length; W -width; D -diameter; n -number of specimens measured; all measurements are given in micrometers (µm).Diagnosis.Larvae: Distance between bases of trichobothria Oi larger than their length; all dorsal hysterosomal setae subequal; excretory pore plate wider than long; basal segment of chelicera with narrow strips; I/II-Leg-4 solenidion much longer than eupathidium, I-Leg-6 de < ds; adults: frontal plate subquadrate (L/W ratio 0.88-1.05),anterolateral extensions much wider than posterolateral extensions, anterior margin obtuse angled or slightly convex, posterior margin straight, posterior projections short, their length equal to 1/4-1/6 length of basal portion of plate, median eye situated at level of anterior setae of plate;  All coxal plates separated on each side (figure 2).Coxal plates II triangular with convex posterior margin, coxal plates I and III more or less trapezoidal and broadly rounded medially, all coxal setae short and subequal.Urstigma comparatively large oval and wider than long.Setae Se, Ci, Pi and Pe subequal and slightly longer than both pairs of anal setae (Ai, Ae).
Capitulum (figure 6) with short, wide base, ventral setae slightly shorter than dorsal ones.The mouth opening surrounded by numerous long papillae.Posterior portion of basal part of capitulum with distinct reticulations.Basal segment of chelicera (figure 7) with narrow strips, cheliceral stylet heavy and without apical teeth.
Pedipalps moderately long (figure 8): P-1 short, without setae; P-2 large with convex dorsal margin and single dorsal seta located in proximal part of segment; P-3 with two unequal setae (thick proximal and relatively long, thin distal); P-4 with three unequal setae and large dorsodistal bifurcate claw; P-5 small, with a moderately long solenidion and seven setae, five long an thick, two relatively short and thin.
All coxal plates with numerous setae (figure 26).Genital field (figure 27) with three pairs of acetabula, anterior pair of acetabula larger than second pair but slightly smaller than posterior pair of acetabula.Acetabular plate elongate (L/W ratio 2.18-2.42),with 15-20 pairs of medial setae; posterior margin of plate oblique in antero-lateral direction.