Hygrobates japonicus Uchida 1931

Matsumoto, Noriko, Dick, Matthew H. & Mawatari, Shunsuke F., 2005, Water mites of the genus Hygrobates Koch, 1837 (Acari: Parasitengona: Hygrobatidae) from Hokkaido, northern Japan, Journal of Natural History 39 (21), pp. 1893-1945 : 1914-1919

Hygrobates japonicus Uchida 1931

( Figures 11 , 12 )

Hygrobates japonicus Uchida 1931, p 265 –266, Abb. 5–8.

Hygrobates (s. str.) japonicus: Sokolow 1940, p 293 , Figure 153a, b.

Hygrobates bituberosus Sokolow 1931, p 488 –490, Figures 49, 50.

Material examined

Lectotype (ZIHU-2330): adult female, missing chelicerae, dissected and mounted in glycerin jelly, from Shakujii , Tokyo, 15 April 1928, labelled Hygrobates sp. in Uchida collection . Paralectotype (ZIHU-2331): adult male, missing the palps, dissected and mounted in glycerin jelly, from Shakujii , Tokyo, 15 April 1928 , labelled Hygrobates sp. in Uchida collection; adult male from Shakujii , Tokyo, 17 August 1933; four females from Turui, Akan , Hokkaido, 7 October 2002 .

Description of female

Lectotype, ZIHU-2330.

Cuticular features. Integument soft, finely striated, spacing of striae 1.8. Coxoglandularia II ( Figure 11D ) without secondary sclerotization. Antenniform setae ( Figure 11E ) thin, on small, oval base, length 23. Without dorsalia.

Chelicera. Missing.

Palp ( Figure 11B ). Length/height, P-1 45/65, P-2 175/123, P-3 117/84, P-4 227/55, P-5 71/19. P-2 with tapering, truncated projection, with seven denticles on flattened top. Ventral side of P-3 swollen into a rounded knob, with a dense patch of 27 denticles on top occupying less than one-quarter of the ventral segment length. P-4 with two ventral setae and seven setae on lateral and dorsal sides. P-4 setae ratio 0.2. P-5 with three setae.

Capitulum ( Figure 11A ). Broadly fused with the first coxae. Anterior border of each half of capitulum is irregularly truncate, without a notch.

Coxae ( Figure 11A ). Length/width anterior coxal group 356/330. Length/width posterior coxal groups 356/324. Posterior end of anterior coxal group rounded-triangular; posterolateral apodemes extending slightly beyond sclerotization, 207 from tip to tip. Suture line between first coxae and capitulum nearly straight. Coxoglandularium I on Cx2. Suture line between third and fourth coxae incomplete, extending to near glandularium of Cx4. Medial margin of Cx4 a rounded angle, with angle apodemes.

Legs ( Figure 12A–D ). Swimming hairs absent, claws with a ventral clawlet. Lengths of leg segments I-L-1 to I-L-6, 58/136/143/207/220/207; II-L-1 to II-L-6 84/110/156/240/–/–; III-L-1 to III-L-6, 79/123/168/253/279/272; IV-L-1 to IV-L-6, 149/181/233/369/162/324. Seta to tibia ratio, I-L to IV-L, 0.38/–/0.25/0.68 (II-L-5 and 6 are missing).

Genital field ( Figure 11F ). Entire genital field 194 in width. Length/width genital plates 201/100; outer border irregularly crenate except around smooth proximolateral portion; 19 setae on right side and 20 on left. No setae on membranous integument near genital plates. Three pairs of genital acetabula arranged in an obtuse triangle. Distance between Ac1 and Ac2, and Ac2 and Ac3, less than width of Ac1. Length/width Ac1 78/45, Ac2 71/39, Ac3 71/45. Pre- and postgenital sclerites with medially protruded apodemes. No setae on pregenital sclerite. Pregenital sclerite extends slightly anterior to anterior ends of genital plates. Postgenital sclerite anterior to the posterior ends of genital plates. Genital opening between pre- and postgenital sclerites 162 in length.

Description of male

Paralectotype; ZIHU-2331. Characters as given for female, except for genital field. Chelicerae and palps missing.

Capitulum. Width 117.

Coxae. Length/width anterior coxal group 324/408. Length/width posterior coxal group 324/298. Posterolateral apodemes of anterior coxal group 188 from tip to tip.

Legs. Lengths of leg segments I-L-1 to I-L-6, 52/117/130/181/194/181; II-L-1 to II-L-6 45/117/130/181/194/181; III-L-1 to III-L-6, 78/123/168/253/279/272; IV-L-1 to IV-L-6, 162/168/233/343/350/305. Seta to tibia ratio, I-L to IV-L, 0.50/0.43/0.40/0.37.

Genital field ( Figure 11G ). Genital plate length/width 194/240; outer border irregularly crenate with three distinct lobes. Middle third of anterior border raised as a rounded projection; posterior border irregular, with a wide, shallow median notch; apodemes lacking. Genital plate with 22 setae on right side and 23 on left. Three genital acetabula on each side, arranged in an obtuse triangle. Distance between Ac1 and Ac2, and Ac2 and Ac3, less than width of Ac1. Length/width Ac1 65/45, Ac2 75/39, Ac3 71/36.

Variation in measurements, female

ZIHU-3088, 3089, 3090, and specimens from first author’s personal collection. Antenniform setae length 40 (36–42, n 53).

Chelicera. Total length 391 (369–421, n 54), basal segment 284 (266–311, n 54), claw 120 (117–123, n 54), maximum height 77 (71–81, n 54), length/height ratio 5.1 (4.9–5.2, n 54), basal segment/claw ratio 2.4 (2.3–2.5, n 54).

Palps. Length/height P-1 37/57 (32–39/52–58, n 54), P-2 154/97 (149–156/91–104, n 54), P-3 112/66 (104–117/58–78, n 54), P-4 213/46 (201–224/45–49, n 54), P-5 65/21 (65–65/ 19–26, n 54). P-2 with 18 (15–22, n 54) denticles. P-3 with 17 (13–24, n 54) denticles. Terminal end of P-4 with nine (8–11, n 54) setae. P-4 setae ratio 0.2 (0.2–0.3, n 54). P-5 with three setae.

Capitulum. Width 160 (149–175, n 54).

Coxae. Length/width anterior coxal group 335/403 (318–350/389–421, n 54). Length/ width posterior coxal group 315/274 (288–337/266–285, n 54). Posterolateral apodemes of anterior coxal group 190 (168–201, n 54) from tip to tip.

Legs. Lengths of leg segments I-L-1 to I-L-6, 71/123/139/194/215/207 (65–78/117–130/ 136–143/188–201/207–227/201–214, n 54); II-L-1 to II-L-6 75/124/153/227/248/233 (71–78/97–139/146–162/220–233/240–259/227–240, n 54); III-L-1 to III-L-6, 79/141/ 178/274/306/285 (58–84/136–143/168–188/266–285/298–318/279–298, n 54); IV-L-1 to IV-L-6, 159/183/245/366/388/330 (149–175/162–207/227–259/356–376/382–399/324– 337, n 54). Seta to tibia ratio, I-L to IV-L, 0.45/0.44/0.41/0.34 (0.42–0.47/0.38–0.50/ 0.36–0.45/0.32–0.40, n 54).

Genital field. Entire genital field 269 (243–292, n 54) in width. Length/width genital plates 169/96 (162–175/84–104, n 54). Genital plates with 15 (13–17, n 54) setae on right and 15 (14–16, n 54) on left. Length/width Ac1 61/35 (52–65/32–39, n 54), Ac2 71/33 (58–78/32– 36, n 54), Ac3 60/42 (52–68/39–45, n 54). Genital opening between pre- and postgenital sclerites 133 (130–143, n 54) in length.

Variation in measurements, male

ZIHU-2333, Uchida collection.

Chelicera. Total length 363, basal segment 272, claw 123, maximum height 78, length/ height ratio 4.7, basal segment/claw ratio 2.2.

Palps. Length/height P-1 32/52, P-2 143/91, P-3 104/58, P-4 214/42, P-5 71/23. P-2 with 19 denticles. P-3 with 18 denticles. P-4 with seven setae on end. P-4 setae ratio 0.2. P-5 with three setae.

Capitulum. Width 104.

Coxae. Length/width anterior coxal group 324/467. Length/width posterior coxal group 343/285. Posterolateral apodemes of anterior coxal group 194 from tip to tip.

Legs. Lengths of leg segments I-L-1 to I-L-6 65/130/149/201/227/214; II-L-1 to II-L-6, 65/117/162/233/253/246; III-L-1 to III-L-6, 78/117/20/279/318/298; IV-L-1 to IV-L-6, 181/194/240/363/389/337. Seta to tibia ratio, I-L to IV-L 0.5/0.5/0.4/0.4.

Genital field. Entire genital field 253 in width. Genital plates with 16 setae on right and 19 on left. Length/width Ac1 65/39, Ac2 78/32, Ac3 68/52. Genital opening between pre- and postgenital sclerites 136 in length.

Localities

Tokyo; Akan on Hokkaido.

Distribution

Middle and northern Japan; eastern Russia (Primorsk, Sokolow 1940). Uchida (1936a), in his redescription of H. japonicus erroneously based on specimens of H. longipalpis (see below), noted that ‘‘This species is common also in Sapporo’’. In fact, his specimens labelled H. japonicus from Sapporo include both H. longipalpis and H. bibi , but not H. japonicus .

Remarks

Uchida (1931) described this species based on two specimens from Tokyo, Japan. We located these specimens in Uchida’s collection by comparing the collection data cited in the original description with information on the specimen labels. Since Uchida did not designate types for the species, we have designated one of the specimens as the lectotype and the other as a paralectotype for H. japonicus . The male specimen designated as the paralectotype lacks palps; therefore, we used another specimen from Uchida’s collection, confirmed by us to be H. japonicus , for observation of the male palps. These three specimens had been labelled by Uchida only as ‘‘ Hygrobates sp. ’’ The collection contained another 25 specimens labelled as H. japonicus . Among these, only one specimen proved to be H. japonicus ; the rest were either H. bibi or H. longipalpis .

Uchida (1936a) redescribed H. japonicus on the basis of over 20 specimens collected from Kunashiri Island, off the north-west tip of Hokkaido. By comparing the collection data cited in his text with information on specimen labels, we located in Uchida’s collection the specimens he used for the redescription, all labelled H. japonicus . Interestingly, all of these proved to be H. longipalpis ! Uchida’s redescription is far from current standards and of no use in discriminating H. japonicus from H. longipalpis , because nine characters we have found useful to distinguish between the two were poorly described, with no illustrations. For example, Uchida did not mention whether the posterior end of the anterior coxal group is round versus triangular, nor whether the suture line between Cx3 and Cx4 is complete versus incomplete, both of which are diagnostic between H. japonicus and H. longipalpis . Likewise, he indicated the shape of the P-2 projection only as ‘‘blunt’’ and failed to note the distribution of denticles, and he failed to describe adequately the shape of the male genital plate and the position of the pregenital sclerite of the female.

Hygrobates japonicus is, in fact, most similar to H. longipalpis ; the two share nine of 18 characters (Table II). In particular, only these two species have P-3 with a prominent ventral convexity bearing a compact, limited denticulate patch. The most important character diagnostic for H. japonicus is the flat end of the P-2 projection, which separates it from the other six Japanese species in the subgenus Hygrobates .

Figures

Figure 11. Hygrobates (Hygrobates) japonicus. (A–F) Female. (A) Ventral side, scale 1; (B) palp, scale 3; (C) chelicera, scale 2; (D) coxoglandularium II, scale 3; (E) antenniform seta, scale 3; (F) genital field, scale 3. (G) Male, paralectotype (ZIHU-2331), genital field, scale 3. Scale bars: 1, 2, 3 (B, F, G)5100 mm; 3 (D, E)550 mm.

Figure 12. Hygrobates (Hygrobates) japonicus, female. (A) First leg; (B) second leg; (C) third leg; (D) fourth leg. Scale5100 mm.