Hygrobates ezoensis ( Uchida, 1934 )

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 : 1935-1942

Hygrobates ezoensis ( Uchida, 1934)

( Figures 21–23 )

Rivobates ezoensis Uchida 1934, p 92 –95, Figures 26–28.

Hygrobates (Rivobates) ezoensis: Imamura 1954, p 82 –84, Figure 48.

Hygrobates (Rivobates) diversiporus: Imamura 1980, p 350 –351, Figure 163B.

Hygrobates diversiporus: Uchida 1936b, p 314 –315.

Material examined

Lectotype: ZIHU-2362, Uchida’s collection, adult male, dissected and mounted in glycerin jelly, from Chitose , Hokkaido, 6 February 1932, labelled Rivobates ezoensis collected by H. Ishizuka. Allolectotype: ZIHU-2368, adult female with damaged chelicerae, Uchida’s collection, adult male, dissected and mounted in glycerin jelly, from Chitose , Hokkaido, 6 February 1932, labelled Rivobates ezoensis collected by H. Ishizuka. Paralectotypes: adult males (ZIHU-2361, 2363) and adult females (ZIHU-2364, 2365, 2366, 2367), Uchida’s collection, dissected and mounted in glycerin jelly, from Chitose , Hokkaido, 6 February 1932, labelled Rivobates ezoensis collected by H. Ishizuka.

Additional material. Two adult females (ZIHU-2381, 2382) and five adult males (ZIHU- 2376, 2377, 2378, 2379, 2380), Uchida’s collection, dissected and mounted in glycerin jelly, from a river near Yuzhno-Sakhalinsk , Sakhalin, 4 August 1936 , labelled Rivobates diversiporus collected by H. Yamaguchi. One adult female from a stream in Akan , 4 June 2002 ; five adult females and six adult males from a spring in Bihoro , 13 August 2002 ; three adult females from Moizari-gawa River, Eniwa , 11 May 2002 ; one adult male from Kashiwagi-gawa River, Eniwa , 19 May 2002 ; two adult males from Moizari-gawa Rover, Eniwa , 30 July 2002 ; one adult male from Horonobe , 20 August 2002 ; three adult females from a spring in Turui , 9 February 2001 ; one adult female from a spring in Turui , 26 February 2001 ; three adult females from a pond in Turui , 15 July 2003 ; one adult female from a spring in Masuhoro, Wakkanai , 6 July 2002 .

Description of female

Description and measurements from allolectotype, ZIHU-2368; figures from other specimens.

Cuticular features. Integument soft, very finely striated, spacing of striae 0.7. Secondary sclerotization of coxoglandularia II weak ( Figure 21D ). Antenniform setae missing from specimen. Without dorsalia.

Chelicera. Damaged on this specimen. Palp. Length/height P-1 32/39, P-2 78/78, P-3 104/78, P-4 149/45, P-5 58/19. P-2 with pronounced, tapering, acute ventral projection at distal margin, with 12 denticles distributed to base of projection. Ventral side of P-3 swollen, convex in outline, with a patch of 18 denticles occupying less than half the ventral side, offset toward distal end. P-4 with two ventral setae and 10 setae on lateral and dorsal sides. P-4 setae ratio 0.07. P-5 with three setae.

Capitulum ( Figure 21A ). Fused with the first coxae, 104 in width. Anterior portion of each half of capitulum with a rounded notch.

Coxae ( Figure 21A ). Length/width anterior coxal group 318/402. Length/width posterior coxal group 337/279. Posterior end of anterior coxal group broadly rounded; posterolateral apodemes extend slightly beyond sclerotization, 188 from tip to tip. Suture line between first coxae and capitulum irregular, not curved. Coxoglandularium I on Cx2. Suture line between Cx3 and Cx4 incomplete, extending to near glandularium of Cx4. Medial margin of Cx4 variable (evenly rounded or with a rounded angle projecting in middle), without angle apodemes.

Legs ( Figure 22A–D ). Swimming hairs absent, claws with a ventral clawlet. Lengths of leg segments I-L-1 to I-L-6, 71/84/117/181/194/181; II-L-1 to II-L-6 71/84/143/194/220/220; III-L-1 to III-L-6, 65/104/110/156/175/181; IV-L-1 to IV-L-6, 156/143/207/279/292/246. Seta to tibia ratio, I-L to IV-L, 0.40/0.35/0.44/0.31.

Genital field ( Figure 21F ). Entire genital field 318 in width. Genital plates with somewhat irregular outer border. Right genital plate with 16 setae, left with 16. No setae on membranous integument near genital plate. Length/width genital plates 149/91. Genital acetabula closely packed in each genital plate, seven on left side, six on right ( Figure 21F is from a female specimen other than allolectotype). Pre- and postgential sclerites each with a median apodeme. No setae on pregenital sclerite. Pregenital sclerite located anterior to the anterior ends of genital plates. Postgenital sclerite located anterior to the posterior ends of genital plates. Genital opening between pre- and postgenital sclerites.

Description of male

Lectotype, ZIHU-2362. Characters same as for female, except for genital field. Antenniform setae missing from specimen.

Chelicera. Missing from specimen.

Palp ( Figure 21B ). Length/height P-1 32/45, P-2 84/91, P-3 84/78, P-4 149/52, P-5 55/23. P-2 with 13 denticles. P-3 with 22 denticles. P-4 with two ventral setae and 10 setae on lateral and dorsal sides. P-4 setae ratio 0.1. P-5 with three setae.

Capitulum. Width 97.

Coxae. Length/width anterior coxal group 324/389. Length/width posterior coxal groups 324/311. Posterolateral apodemes of anterior coxal group 188 from tip to tip.

Legs. Lengths of leg segments I-L-1 to I-L-6, 84/130/130/175/181/181; II-L-1 to II-L-6 78/110/143/181/194/194; III-L-1 to III-L-6, 65/84/149/201/240/220; IV-L-1 to IV-L-6, 143/162/194/279/305/253. Seta to tibia ratio, I-L to IV-L, 0.38/0.47/0.30/0.26.

Genital field ( Figure 21G ). Genital plate length/width 188/227, with smooth outer border. Anterior end of genital plate a rounded obtuse angle, with a medial apodeme extending from anterior margin of gonopore. Posterior end of genital plate variable, from flat to curved, with one to three rounded apodemes ( Figure 23A–K ). Genital plate with 22 setae on right side and 25 on left. Genital acetabula eight on left side, seven on right; Figure 21G based on a specimen other than lectotype.

Variation in measurements, female

Antenniform setae length 70 (58–78, n 54).

Chelicera. Total length 313 (279–350, n 53), basal segment 231 (207–259, n 53), claw 95 (84–104, n 53), maximum height 67 (65–71, n 53), length/height ratio 4.7 (4.3–4.9, n 53), basal segment/claw ratio 2.4 (2.3–2.5, n 53).

Palp. Length/height P-1 30/38 (26–32/32–42, n 55), P-2 111/66 (104–117/58–74, n 55), P-3 80/47 (71–97/39–58, n 55), P-4 143/42 (136–149/39–55, n 55), P-5 51/20 (45–55/19– 23, n 55). P-2 with nine (6–12, n 55) denticles. P-3 with 10 (6–17, n 55) denticles. P-4 with two ventral setae and 11 (8–13, n 55) setae on lateral and dorsal sides. P-4 setae ratio 0.1 (0.0–0.1, n 55). P-5 with three setae.

Capitulum. Width 87 (78–97, n 55).

Coxae. Length/width anterior coxal group 287/394 (272–298/356–486, n 55). Length/ width posterior coxal groups 301/250 (272–324/214–266, n 55). Posterolateral apodemes of anterior coxal group 154 (146–162, n 55) in width.

Legs. Length of leg segments I-L-1 to I-L-6 60/92/114/158/170/171 (52–65/84–97/110– 123/156–162/162–175/162–181, n 55); II-L-1 to II-L-6 62/98/114/165/183/184 (58–65/ 97–104/110–117/156–175/175–194/175–207, n 55); III-L-1 to III-L-6 66/106/136/197/ 211/211 (58–78/97–130/130–143/188–207/201–220/201–227, n 55); IV-L-1 to IV-L-6 130/150/193/257/271/192 (117–143/143–162/181–207/240–266/259–285/227–259, n 55, IV-L-6 only n 54). Seta to tibia ratio, I-L to IV-L 0.4/0.4/0.3/0.3 (0.3–0.4/0.3–0.4/0.3–0.3/ 0.3–0.3, n 55).

Genital field. Entire genital field 264 (207–298, n 55) in width. Right genital plate with 15 (15–16, n 55) setae, left with 13 (12–14, n 55). Length/width genital plates 131/79 (110–143/65–91, n 55). Genital acetabula eight (6–10, n 55) on left side, seven (6–9, n 55) on right. Genital opening between pre- and postgenital sclerites 148 (104–181, n 55) in length.

Variation in measurements, male

Antenniform setae length 58 (n 51). Chelicera ( Figure 22C ). Total length 300 (272–311, n 54), basal segment 222 (201–233, n 54), claw 91 (84–97, n 54), maximum height 64 (58–68, n 54), length/height ratio 4.7 (4.2–5.2, n 54), basal segment/claw ratio 2.5 (2.3–2.6, n 54).

Palp. Length/height P-1 31/36 (26–32/32–45, n 55), P-2 105/67 (91–110/52–78, n 55), P- 3 74/47 (65–84/39–52, n 55), P-4 139/40 (123–143/32–49, n 55), P-5 49/18 (42–52/13– 23, n 55). P-2 with 11 (7–15, n 55) denticles. P-3 with 15 (13–17, n 55) denticles. P-4 with two ventral setae and 11 (9–12, n 55) setae on lateral and dorsal sides. P-4 setae ratio 0.05 (0.02–0.07, n 55). P-5 with three setae.

Capitulum. Width 87 (84–97, n 55).

Coxae. Length/width anterior coxal group 277/353 (246–292/324–376, n 55). Length/ width posterior coxal group 290/250 (240–311/207–272, n 55). Posterolateral apodemes of anterior coxal group 149 (123–168, n 55) from tip to tip.

Legs. Length of leg segments I-L-1 to I-L-6 58/99/111/153/166/165 (52–65/78–110/104– 117/136–162/149–175/149–181, n 55); II-L-1 to II-L-6 56/96/115/164/181/183 (45–65/ 78–110/110–123/143–175/162–207/168–201, n 55); III-L-1 to III- L-6 65/101//130/193/ 211/205 (52–71/91–110/117–143/175–201/188–227/188–214, n 55); IV-L-1 to IV-L-6 141/148/184/240/257/232 (130–156/130–162/168–194/207–266/227–272/207–246, n 55). Seta to tibia ratio, I-L to IV-L 0.4/0.3/0.3/0.3 (0.4–0.4/0.3–0.4/0.2–0.3/0.2–0.3, n 55).

Genital field. Length/width 158/202 (130–175/162–227, n 55). Genital plate with 22 (19–26, n 55) setae on right side and 21 (18–23, n 55) on left side. Genital acetabula eight (6–10, n 55) on left side, seven (6–9, n 55) on right.

Localities

Akan, Bihoro, Eniwa, Horinobe, Turui, Wakkanai, all on Hokkaido.

Distribution

Sakhalin and Hokkaido.

Remarks

Uchida (1934, p 95) described Hygrobates ezoensis under the name of Rivobates ezoensis , based on ‘‘many specimens’’ collected by Mr H. Ishizuka from a spring in Chitose, Hokkaido on 6 February 1932. Soon after, however, Uchida (1936b) declared his species a junior synonym of Rivobates diversiporus Sokolow, 1927 , based on ‘‘more than 10 examples collected by Mr. H. Yamaguchi on August 4, 1936 in a river near Toyohara’’, Sakhalin Island.

We found in Uchida’s collection eight specimens separately mounted on slides and labelled ‘‘ Rivobates ezoensis, Chitose (Hokkaido) Feb. 6, 1932 ’’, and seven slides labelled ‘‘ Rivobates diversiporus (Sokolow) Karahuto, Toyohara Aug. 4, 1936 H. Yamaguchi’’. Karahuto is the Japanese name for Sakhalin Island and Toyohara is the old Japanese name for Yuzhno-Sakhalinsk on Sakhalin. In a careful examination, we could not detect any diagnostic differences in characters among these specimens from Uchida’s collection and about 30 specimens we collected from various localities on Hokkaido for our study. Thus we confirmed that the species of the subgenus Rivobates that we collected on Hokkaido is the same that Uchida identified from both Hokkaido and Sakhalin. The question remained as to the species’ identity.

The taxonomy of H. ezoensis / diversiporus has been convoluted. In his original description, Uchida (1934, p 95) noted for Rivobates ezoensis , ‘‘The species is easily distinguished … from R. diversiporus (Sokolow) by the form of the third epimera and genital plates’’. However, in later synonymizing Rivobates ezoensis with R. diversiporus, Uchida (1936b, p 314) concluded that ‘‘these differences are due to individual variations’’ and remarked that ‘‘Sokolow’s specimens are probably somewhat aberrant ones of the species’’. Imamura (1954), on the other hand, did not agree with this synonymy and stated, ‘‘it [ H. ezoensis ] is distinguished from the latter [ H. diversiporus ] in the shapes of genital plates of both sexes’’. Nonetheless, Viets (1956) accepted the synonymy, and Imamura (1980) listed H. diversiporus in an illustrated encyclopaedia of Japanese mites and ticks, to the exclusion of H. ezoensis .

We examined the male genital plate of 18 specimens from Sakhalin and Hokkaido, of which 11 are illustrated in Figure 23A–K , including three of Uchida’s specimens of H. ezoensis from Chitose, Hokkaido ( Figure 23C, D, G ); three of Uchida’s specimens from Sakhalin labelled as H. diversiporus ( Figure 23H, J, K ); and five specimens we collected from northern ( Figure 23A, B, E ) and central ( Figure 23F, I ) Hokkaido. In all 18 specimens examined, the male genital plate is irregularly ovoid, with the anterior border a rounded obtuse angle and the posterior border straight, irregularly convex, or broadly curved (that in Figure 23H is atypical, likely due to a developmental anomaly or healed wound). This form of the male plate is just as originally figured by Uchida (1934, p 93, Figure 26) for Rivobates ezoensis . It differs from the male plate ( Figure 23L ) of H. diversiporus originally described by Sokolow (1927) as ‘‘verkehrt-herzförmiger’’ (reverseheart-shaped; our translation), with an acute anterior angle and a depressed posterior border having a broad, rounded median notch. We thus conclude that H. ezoensis ( Uchida, 1934) is a valid species, distinct from H. diversiporus Sokolow, 1927 , and that the name H. ezoensis should be restored. Unfortunately, the male genital plate seems to be the salient difference between the two species, as we detected no clear diagnostic differences in the female genital plates or other characters.

Since Uchida (1934) did not designate types for the species, one of the male specimens from his collection is here designated as lectotype (ZIHU-2362) and one of the female specimens (ZIHU-2368) is designated as allolectotype of H. ezoensis ( Uchida, 1934) .

Another Japanese species in the subgenus Rivobates , H. taniguchii , was described by Imamura (1954) on the basis of the two specimens collected from Kamishokotsu, Hokkaido. Despite extensive collecting across Hokkaido, we did not find this species.

Figures

Figure 21. Hygrobates (Rivobates) ezoensis. (A–F) Female. (A) Ventral side, scale 1; (B) palp, scale 2; (C) chelicera, scale 1; (D) coxoglandularium II, scale 2; (E) antenniform seta, scale 2; (F) genital field, scale 2. (G) Male, genital field, scale 2. Scale bars: 1, 2 (B, F, G)5100 mm; 2 (D, E)550 mm.

Figure 22. Hygrobates (Rivobates) ezoensis, female. (A) First leg; (B) second leg; (C) third leg; (D) fourth leg. Scale bar: 100 mm.

Figure 23. Male genital field of Hygrobates ezoensis and H. diversiporus. (A–K) H. ezoensis: (A, B) from Bihoro, northern Hokkaido; (C) lectotype, ZIHU-2362, (D) syntype, ZIHU-2361, (G) syntype, ZIHU-2363 from Chitose, southern Hokkaido; (E) from Horonobe, northern Hokkaido; (F, I) from Eniwa, central Hokkaido; (H) ZIHU-2379, (J) ZIHU-2378, (K) ZIHU-2377, from Toyohara, Sakhalin Island. (L) H. diversiporus, taken from Sokolow (1940).