New records of water mites of the family Sperchontidae Thor, 1900 from China (Acari, Hydrachnidia), with descriptions of two new species

Abstract Five species of water mites of the family Sperchontidae Thor, 1900 are reported from China. Two of them are new to science, Sperchon (Sperchon) orbipatella sp.n. and Sperchon (Sperchon) urumqiensis sp. n., and the other three are new to China, i.e., Sperchon (Palpisperchon) nikkoensis Imamura, 1976, Sperchon (Sperchon) sounkyo Imamura, 1954 and Sperchonopsis (Sperchonopsella) whiteshellensis Conroy, 1991. The first descriptions of the female of Sperchon nikkoensis and the male of Sperchon sounkyo are also given. The subgenus Sperchonopsella Conroy is new to the fauna of China.

All the type specimens are deposited in the Institute of Entomology, Guizhou University, China (GUGC).
All measurements are given in µm with the mean first, followed by the range in bracket.

Remarks.
At present, only five species of the subgenus Palpisperchon Lundblad, 1941 are known: Sperchon crassipalpis Marshall, 1933, S. distans Scheffler, 1972, S. mirabilis Lundblad, 1941, S. nikkoensis Imamura, 1976and S. skopetsi Tuzovskij, 1982 Due to the shape of cuticle, E4 absent from CxIII, P-II with a very long ventrodistal projection, and P-IV with two greatly enlarged ventral peg-like setae, the specimens from China show a general conformity with S. (P.) nikkoensis, a species previously known only from the female sex from Japan (Imamura 1976). However, the absence of pregenital sclerite and the presence of a round platelet in front of the genital field (as reported in the original illustration, see Imamura 1976), are typical characters of the male sex (Di Sabatino et al. 2010). Therefore, the specimen described by Imamura should be a male instead of female. This is the first description of the opposite sex to that in original description (Imamura 1976), and first record of this species from China.
Distribution. China (present study); Japan (Imamura 1976).  Cuticle covered with small papillae various in shape; excretory pore surrounded by a sclerotized ring; the second acetabulum near to the third but far away from the first one; P-II with a long ventro-distal projection and one thick seta at the base of the projection; third to fifth segments of leg I-IV with rather short plumose setae in longitudinal rows.
Description. Male (n=3): Idiosoma oval in outline, 636 (602-783) in length, 533 (510-563) in width. Cuticle yellow-brown, covered with small, various shaped papillae (Fig. 13). A1 smooth, short and thick, other glandularia thin and longer. Cuticle without an extended dorsal and ventral plate. Glandularia and O2 encircled by small rounded platelets (Fig. 11, Fig. 12). Coxae in four groups, surface of coxae reticulated. ACG 162 (153-176) in length, close to each other but not fused, posterior apodeme weakly developed. E2 laterally between ACG and PCG. PCG 239 (228-257) in length. E4 close to anterior margin of CxIII. Distance between anterior end of ACG and posterior end of PCG 387 (364-412). Genital field between PCG with a small and rounded platelet in front. Genital valves not covering the genital acetabula, 170 (157-184) in length, 140 (132-165) in width. Pre-and postgenital sclerites not developed. Three pairs of small and rounded genital acetabula, the second acetabulum near to the third and far away from the first. V1 on very small sclerites and without accompanying glandularia. Excretory pore surrounded by a sclerotized ring and placed anterior to the line of V2 glands.
Female ( Etymology. The species is named after the shape of the three acetabula, "orbi-" Latin word, means rounded.
Remarks. All the species of the genus Sperchon have three pairs of acetabula, in most cases arranged almost equidistantly, usually the anterior two pairs of acetabula elongated while the posterior pair is somewhat rounded. However, in some species such as Sperchon prosperoides Tuzovskij, 1990 andS. minutiporus Sokolow, 1934, the acetabula are small and rounded, and the second pair shifted near to the third one but far away from the first one.
The new species resembles to Sperchon prosperoides Tuzovskij, 1990, from Russia, from which it can been distinguished by the morphology of the palp and genital field (Tuzovskij 2008). In S. prosperoides, P-III bearing two thick setae on the ventral side and only half of the genital field is located between PCG, whereas in the new species, P-III is without setae on the ventral side and the genital field is located entirely between PCG.
Distribution. China (Xinjiang Uygur Autonomous Region).  (Fig. 24). A1 short and plumose, setae of other glandularia smooth and relatively long. Cuticle without dorsalia and ventralia except the platelets surrounding glandularia and O2 (Fig. 22, Fig. 23). Coxae in four groups, surface of coxae reticulated. ACG 157 (148-166) in length, apodeme developed. E2 laterally between ACG and PCG. PCG 167 (160-174) in length. E4 on the median and near to inner margin of CxIII. Distance between anterior end of ACG and posterior end of PCG 308 (283-317). Genital field between PCG with a small and rounded platelet in front. Genital valves not covering the genital acetabula, 113 (108-121) in length, 109 (101-114) in width. Pre-and postgenital sclerites visible though not developed. Three pairs of genital acetabula, the first pair of genital acetabula more or less rectangular, the second pair somewhat triangular, and the third pair rounded and larger than the anterior two. V1 on median size sclerites and without accompanying glandularia. Excretory pore without sclerotized ring, and anterior to the line of V2 glands.
Female (n = 3): Similar to male except for the morphology of genital field and the size of idiosoma (Fig. 30, Fig. 31 Imamura, 1954, was firstly described from Japan based on a single female (Imamura 1954), and never recorded since the first description.

Remarks. Sperchon sounkyo
Although the original descriptions and illustrations of S. sounkyo were lacking of some specific features, such as shape of A1 (Fig. 22, Fig. 30) and leg claws (Fig. 28), most characters of our specimens (e.g., shape of cuticle and palp, E4 on CxIII, and excretory pore without sclerotized ring) are in accordance with this species. So we attribute our specimens to S. sounkyo Imamura, 1954. Some differences found in the body size and the number of the setae on the palpal between the Chinese specimens and Japanese specimens should be regarded as the variety between the different populations.
It is the first report from China and the first description of the male of S. sounkyo. This species seems to be a widely distributed species in China.
Distribution. China (present study); Japan (Imamura 1954 Diagnosis. Cuticle covered with scale-shaped papillae; excretory pore surrounded by a sclerotized ring; P-II with a long ventro-distal projection and one heavy seta close to the ventrodistal margin of P-II; third to fifth segments of leg I-IV with rather long plumose setae in longitudinal rows. Description. Male (n = 3): Idiosoma oval in shape, 812 (756-907) in length, 682 (663-712) in width. Cuticle yellow in colour, covered with scale-shaped papillae (Fig.  34). A1 smooth, short and thick, other glandularia thin and long. All glandularia and O2 encircled by a platelet. Some chitinous platelets and glandular platelets on dorsum fused as shown in Fig. 32. Coxae in four groups, surface of coxae reticulated. ACG 163 (158-171) in length, posterior apodeme weakly developed. E2 laterally between ACG and PCG. PCG 242 (236-254) in length. E4 close to anterior margin of CxIII. Distance between anterior end of ACG and posterior end of PCG 443 (432-464). Genital field between PCG with a small and rounded platelet in front. Genital valves not covering the genital acetabula, 188 (182-193) in length, 117 (113-124) in width. Pre-and postgenital sclerites not developed. Three pairs of acetabula, the two anterior pairs of acetabula long elliptic and the posterior pair more or less rounded. An oblong plate posterior to genital field, almost in the middle line of V1 and V3. V1 on very small sclerites and without accompanying glandularia. Excretory pore surrounded by a sclerotized ring and close to the line at V2 glands.
Female (n = 3): Color, idiosoma shape, and the decorations of cuticle as in the male. Characters of the genital field, the fusion and the size of dorsalia and ventralia different from the male (Fig. 41, Fig. 42). Idiosoma 979 (953-1023) in length, 829 Etymology. The species is named after the city where it was collected.
Remarks. Due to the shape of cuticle, E4 on the CxIII and P-II with a long ventro-distal projection, the new species is similar to Sperchon sounkyo Imamura, 1954. From the later species, S. urumqiensis sp. n. can be easily distinguished by the following features: the dorsum and posterior venter with sclerotized muscle attachment plates ( Fig. 32-33, Fig. 41-42) (unsclerotized in S. sounkyo, see Fig. 22-23, Fig. 30-31), the presence of a long and heavy seta close to the ventrodistal margin of P-II (Fig. 40) (vs. without heavy seta in S. sounkyo, see Fig. 27), the two peg-like setae of P-IV are sub- equal in size (Fig. 40) (proximoventral seta larger than distoventral in S. sounkyo, see Fig. 27), and the excretory pore is sclerotized (Fig. 33, Fig. 42) (smooth in S. sounkyo, see Fig. 23, Fig. 31).
The new species also resemble Sperchon ussuriensis Tuzovskij, 2002 from Russia (Tuzovskij 2002). However, in S. ussuriensis, the anterior groups of coxae are fused and the excretory pore is unsclerotized. While in the new species, the anterior groups of coxae are not fused and the excretory pore is surrounded by a sclerotized ring.
Distribution. China (Xinjiang Uygur Autonomous Region).  418 (410-457) in width. Cuticle yellow-brown in color, and covered with papillae. The eye capsules in some young specimens well developed and somewhat projected over the idiosoma margin (Fig. 43). Glandularia greatly enlarged and projected with welldeveloped papillae, and encircled by platelet. Chitinous platelets and glandularia on dorsum and ventrum as showed in Fig. 43 and Fig. 44. Coxae in four groups, surface of coxae reticulated. ACG 152 (151-157) in length, posterior apodeme indistinct. Anterior tip of CxI with a tuft of hair-like setae. E2 laterally between  in length. Glandularia absent from CxIII. Approximately two-thirds of genital field lying between PCG. Genital valves not covering the genital acetabula, 176 (174-188) in length, 145 (143-152) in width. One round platelet in front of genital field. Pre-and postgenital sclerites small. Three pairs of small and rounded genital acetabula, the second pair much close to the third one and far away from the first one. V1 on sclerites in medium size and without accompanying glandularia. Excretory pore lying between V1 and V2 and on a protuberance surrounded by a well-developed sclerotized ring.

Genus
Infracapitulum with a relatively long rostrum, length 196 (194-207). Chelicera total length 207 (204-222), claw length 151 (149-162), basal segment length 56 (55-60), basal segment/claw length ratio 2.7 (2.7). Dorsal lengths of palpal segments: P-I, 24 (24-27); P-II, 104 (101-112); P-III, 94 (92-100); P-IV, 96 (93-105); P-V, 33 (32-36). P-I short and without seta. P-II with a long ventro-distal projection bearing one long and one short setae. About four setae on the lateral and dorsal side of P-II and none of them plumose. P-III with five smooth stae, of them two on the venter and other three on the latero-dorsal side. P-IV without peg-like setae, but with a ventral projection bearing two setae. Two setae on the dorsal and the ventral distal of P-IV Due to the papillate cuticle with the greatly enlarged glandularia, the second and the third pair of acetabula approached to each other and the ventral projections on P-I and P-IV, the specimens from China are similar to S. whiteshellensis from North America (Conroy 1991) and S. nipponicus from Japan (Uchida 1934). The arrangement of dorsalia and ventralia are in a good agreement with description of S. whiteshellensis, and differs from S. nipponicus (see illustration in Uchida 1934). Hence we assigned our specimens to S. whiteshellensis. This is the first record of the subgenus Sperchonopsella from China.