On the taxonomic status of the water mite Hydryphantes hellichi Thon, 1899 (Acari, Hydrachnidia, Hydryphantidae)

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

The aim of the paper is to study the morphology larva, deutonymph and adults of H. hellichi and discuss of the taxonomic status of this species.

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.

Redescription
Larva. Color red. Idiosoma oval, all setae not associated with glandularia (figures 1-2). Proterosoma with two pairs of trichobothria (Fp, Oi) and three pairs of simple setae: Fch, Vi, Oe. Anterior pair of dorsal platelets triangular or oval, trichobothria Fp long and well extending to posterior margin of dorsal plate. Posterior plate wider than long (L/W ratio 0.75-0.90), pentagonal, narrows anteriorly and widens posteriorly; median eye slightly developed (rarely absent) and situated slightly posterior to setae Vi; Fch shorter Vi; Oi short, distance between Oi-Oi larger than their length. Hysterosomal setae Hi, He, Sci, Sce, Li, Le and Si subequal, their bases situated on very small sclerites. All coxal plates separated on each side. Coxal plates II triangular, coxal plates I and III more or less trapezoidal and broadly rounded medially, all coxal setae short and subequal. Urstigma oval and wider than long. Setae Se, Ci, Pi and Pe subequal and slightly longer than both pairs of anal setae (Ai, Ae). Thon, 1899, larva: 10 -I-Leg-4-6; 11 -II-Leg-4-6; 12 -III-Leg-4-6; 13 -claws of leg I; 14 -claws of leg III. Simple setae on I-III-Leg-4-6 are not shown.
Pedipalps moderately long (figure 9): P-1 short, without setae; P-2 large with convex dorsal margin and single dorsal seta proximally to middle of segment; P-3 with two unequal setae (long, thick proximal and relatively short, thin distal); P-4 with three unequal setae and large dorsodistal bifurcate claw; P-5 small with moderately long solenidion, five long, thick and two relatively short, thin unequal setae.
Empodium large and crescent on all tarsi, ambulacra I (figure 13) shorter than ambulacra II and III ( figure 14).
Genital field (figure 27) with three pairs of acetabula and of thin setae; anterior pair of acetabula large than second pair but slightly smaller than posterior pairs of acetabula. Acetabular plate elongate (L/W ratio 2.0-2.5), with 20-30 pairs medial setae.
Thus, the morphology of all active stages of H. hellichi clearly differs from that of H. ruber, and H. hellichi should be treated as a separate species.