Hygrobates nigromaculatus Lebert, 1879

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 : 1928-1931

Hygrobates nigromaculatus Lebert, 1879

( Figures 17 , 18 )

Hygrobates (Hygrobates) nigromaculatus Lebert 1879, p 342 –344.

Material examined

One female and two males from Pashikuru-gawa River, Otobetu , Hokkaido, 11 July 2002 .

Description of male

Based on two specimens, ZIHU-3096 and 3097, collected by first author.

Cuticular features. Integument soft, finely striated, spacing of striae 2.0. Coxoglandularia II ( Figure 17D ) without secondary sclerotization. Antenniform setae ( Figure 17E ) thin and located on small, rounded-triangular bases, length 42 (39–45, n 52). Without dorsalia.

Chelicera ( Figure 17C ). Total length 356 (350–363, n 52), basal segment 266 (259–272, n 52), claw 110 (104–117, n 52), maximum height 81 (78–84, n 52), length/height ratio 4.4 (4.3–4.5, n 52), basal segment/claw ratio 2.4 (2.3–2.5, n 52).

Palp ( Figure 17B ). Length/height P-1 39/45 (39–39/45–45, n 52), P-2 84/75 (84–84/71– 78, n 52), P-3 81/65 (78–84/65–65, n 52), P-4 149/42 (149–149/42–42, n 52), P-5 62/23 (58–65/23–23, n 52). P-2 swollen distally, but ventral border flat. Projection on P-2 broad, indistinct, rounded; 42 (32–51, n 52) denticles cover projection and occupy anterior twothirds of the ventral segment length. P-3 somewhat swollen, but ventral side almost flat, with patch of 33 (31–34, n 52) denticles in middle. P-4 with two ventral setae and 10 (10– 10, n 52) setae on lateral and dorsal sides. P-4 setae ratio 0.01 (0.0–0.02, n 52). P-5 with three setae.

Capitulum ( Figure 17A ). Broadly fused with the first coxae, width 126 (123–130, n 52). Anterior portion of each half of capitulum with a rounded notch.

Coxae ( Figure 17A ). Length/width anterior coxal group 340/399 (330–350/395–402, n 52). Length/width posterior coxal group 353/285 (350–356/272–298, n 52). Posterior end of anterior coxal group broadly rounded; posterolateral apodemes extending slightly beyond sclerotization, 159 (143–175, n 52) from tip to tip. Suture line between first coxae and capitulum nearly straight. Coxoglandularium I on Cx2. Suture line between Cx3 and Cx4 incomplete, extending to near gland of C4. Medial margin of C4 a rounded angle, without angle apodemes.

Legs ( Figure 18A–D ). Swimming hairs absent, claws with a ventral clawlet. Seta to tibia ratio, I-L/IV-L 0.1/0.3 (0.1–0.1/0.2–0.3, n 52).

Genital field ( Figure 17G ). Genital plate length/width 207/243 (207–207/233–253, n 52). Outer border broadly and irregularly crenate; anterior and posterior margins slightly depressed in midline, each with a mammiform medial projection; apodemes lacking. Genital plate with 22 (20–24, n 52) setae on right side and 19 (18–20, n 52) on left. No setae in the membranous integument near genital plate. 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 68/36 (65–71/32–39, n 52), Ac2 71–31 (68–75/32– 39, n 52), Ac3 81–52 (75–87/45–58, n 52).

Description of female

Based on one specimen, ZIHU-3095, collected by first author. Characters same as for male, except for genital field. Antenniform setae length 39.

Chelicera. Total length 363, basal segment 279, claw 113, maximum height 84, length/ height ratio 4.3, basal segment/claw ratio 2.5.

Palp. Length/height, P-1 39/52, P-2 104/84, P-3 91/71, P-4 156/45, P-5 58/26. P-2 with 26 denticles. P-3 with 26 denticles. P-4 with two ventral setae and 11 setae on lateral and dorsal sides. P-4 setae ratio 0.0. P-5 with three setae.

Capitulum. Width 136.

Coxae. Length/width anterior coxal group 363/421. Length/width posterior coxal groups 389/330. Apodemes of anterior coxal group 175 from tip to tip.

Legs. Seta to tibia ratio, I-L/IV-L 0.1/0.2.

Genital field ( Figure 17F ). Entire genital field 298 in width. Genital plates with irregular outer border. Right genital plate with 24 setae, left with 25. No setae in the membranous integument near genital plate. Length/width genital plates 207/110. 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 81/29, Ac2 71/32, Ac3 62/45. Pre- and postgenital sclerites with medially protruded apodemes. No setae on pregenital sclerite. Pregenital sclerite extending 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 175 in length.

Locality

Otobetu on Hokkaido.

Distribution

Palaearctic region: Europe, Russia, Japan (Hokkaido).

Remarks

This is the first record of H. nigromaculatus from Japan. The species is known from Palaearctic Eurasia, with many records from Europe ( Viets 1978). Hygrobates nigromaculatus is most similar to H. foreli (see Remarks for that species), sharing 14 of 18 characters, and next most similar to H. bibi , with which it shares 10 of 18 characters (Table II). Hygrobates nigromaculatus and H. longiporus exclusively have denticles occupying more than half the ventral length of P-2.

Figures

Figure 17. Hygrobates (Hygrobates) nigromaculatus. (A–E, G) Male. (A) Ventral side, scale 1; (B) palp, scale 3; (C) chelicera, scale 2; (D) coxoglandularium II, scale 4; (E) antenniform seta, scale 4; genital field, scale 3. (F) Female, genital field, scale 3. Scale bars: 1, 2, 3, 45100 mm.

Figure 18. Hygrobates (Hygrobates) nigromaculatus, male. (A) First leg; (B) second leg; (C) third leg; (D) fourth leg. Scale bar: 100 mm.