Hygrobates sokolowi ( Thor 1927 )

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 : 1932-1935

Hygrobates sokolowi ( Thor 1927)

( Figures 19 , 20 )

Hygrobates (Rhabdotobates) sokolowi Thor 1927, p 132 –135, Figures 8–10 .

Material examined

Two adult females and two adult males collected from Horonobe, 20 August 2002.

Description of male

Based on two specimens, ZIHU-3093 and 3094, collected by the first author.

Cuticular features. Integument soft, with irregular ridges. Coxoglandularia II ( Figure 19D ) with heavy secondary sclerotization. Antenniform setae ( Figure 19E ) thin, located on small, oval bases, 52 (n 51) in length. Without dorsalia.

Chelicera ( Figure 19C ). Total length 256 (253–259, n 52), basal segment 194 (194–194, n 52), claw 75 (71–78, n 52), maximum height 57 (52–62, n 52), length/height ratio 4.6 (4.2–4.9, n 52), basal segment/claw ratio 2.6 (2.5–2.7, n 52).

Palp ( Figure 19B ). Length/height, P-1 32/33 (32–32/26–39, n 52), P-2 84/68 (71–97/65– 71, n 52), P-3 78/49 (78–78/45–52, n 52), P-4 133/41 (130–136/39–42, n 52), P-5 53/18 (49–58/16–19, n 52). P-2 broad distally, with a long, tapering, acute projection at distal ventral margin; 15 (12–18, n 52) denticles restricted to distal part of projection. Ventral side of P-3 flat, with a patch of 17 (15–18, n 52) denticles covering approximately the anterior half of the ventral surface. P-4 with two ventral setae and 10 (9–11, n 52) setae on lateral and dorsal sides. P-4 setae ratio 0.2 (0.2–0.2, n 52). P-5 with three setae.

Capitulum ( Figure 19A ). Broadly fused with the first coxae, width 96 (94–97, n 52). Anterior portion of each half of capitulum shallowly notched.

Coxae ( Figure 19A ). Length/width anterior coxal group 259/330 (253–266/330–330, n 52). Length/width posterior coxal groups 274/224 (269–279/214–233, n 52). Posterior end of anterior coxal group rounded-triangular; posterolateral apodemes extend slightly beyond sclerotization, 130 (123–136, 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 glandularium of Cx4. Medial margin of Cx4 acute or rounded-angular, with angle apodemes.

Legs ( Figure 20A–D ). Swimming hairs absent, claws with a ventral clawlet. Seta to tibia ratio, I-L/IV-L 0.4/0.3 (0.3–0.4/0.3–0.3, n 52).

Genital field ( Figure 19G ). Genital plate length/width 137/206 (130–143/204–207, n 52), with a smooth, undulating outer border; anterior end flat, coarsely crenate; posterior end with a broad, deep median notch and weak apodemes. Genital plate with 16 (16–16, n 52) setae on right side and 17 (16–17, n 52) on left. Three genital acetabula on each side arranged in an isosceles triangle. Distance between Ac1 and Ac2 greater than width of Ac1; distance between Ac2 and Ac3 greater than or equal to width of Ac1. Length/width Ac1 29/ 18 (29–29/16–19, n 52), Ac2 36/16 (32–39/16–16, n 52), Ac3 28/19 (26–29/19–19, n 52).

Description of female

Based on two specimens, ZIHU-3091 and 3092, collected by the first author. Characters as given for male, except for genital field. Antenniform setae length 45 (45–45, n 52).

Chelicera. Total length 295 (285–305, n 52), basal segment 224 (214–233, n 52), claw 84 (84–84, n 52), maximum height 68 (65–71, n 52), length/height ratio 4.4 (4.3–4.4, n 52), basal segment/claw ratio 2.7 (2.5–2.8, n 52).

Palp. Length/height P-1 32/34 (32–32/32–36, n 52), P-2 115/67 (113–117/65–68, n 52), P-3 84/52 (84–84/49–55, n 52), P-4 150/39 (143–156/39–39, n 52), P-5 50/18 (45–55/16–19, n 52). P-2 with 21 (19–23, n 52) denticles. P-3 with 24 (23–24, n 52) denticles. P-4 with two ventral setae and 11 (10–11, n 52) setae on lateral and dorsal sides. P-4 setae ratio 0.4/0.3 (0.3–0.4/0.2–0.3, n 52). P-5 with three setae.

Capitulum. Width 97 (78–117, n 52).

Coxae. Length/width anterior coxal group 243/340 (233–253/324–356, n 52). Length/ width posterior coxal group 274/269 (269–279/259–279, n 52). Apodemes of anterior coxal group 136 (136–136, n 52) from tip to tip.

Legs. Seta to tibia ratio, I-L/IV-L 0.3/0.2 (0.3–0.4/0.2–0.3, n 52).

Genital field ( Figure 19F ). Entire genital field 206 (204–207, n 52) in width. Outer border of genital plates smooth; right genital plate with 14 (13–14, n 52) setae, left with 13 (12–14, n 52). No setae on the membranous integument near genital plate. Length/width genital plates 143/72 (143–143/65–78, n 52). Three genital acetabula on each side, arranged in an obtuse triangle. Distance between Ac1 and Ac2 greater than width of Ac1; distance between Ac2 and Ac3 less than width of Ac1. Length/width Ac1 31/23 (29–32/19–26, n 52), Ac2 39/18 (39–39/16–19, n 52), Ac3 34/21 (32–36/19–23, n 52). Pre- and postgenital sclerites with medially protruded apodemes. No setae on pregenital sclerite. Pregenital sclerite extends anterior to the anterior ends of genital plates. Postgenital sclerite extends posterior to the posterior ends of genital plates. Genital opening between pre- and postgenital sclerites 125 (120–130, n 52) in length.

Locality

Horonobe on Hokkaido.

Distribution

Eastern Europe and northern Japan: Caucasus, western Russia, Hokkaido.

Remarks

This is the first record of H. sokolowi from Japan. The species was previously known only from western Russia ( Thor 1927; Sokolow 1940; Sokolow and Jankowskaja 1962; Viets 1978). Among the eight Hokkaido species in the subgenus Hygrobates , H. sokolowi is unique in having the acetabula small in relation to the area of the genital plate, so that most of the central portion of the plate is unoccupied by acetabula. At the Hokkaido locality, H. sokolowi was collected among stones on the bottom of a tributary of the Toikanbetsu River, together with two specimens of H. longiporus .

Figures

Figure 8. P-2 palp segment of Hygrobates calliger and H. heteropalpis. (A–C) European specimens of H. calliger; (D– H, K) Hokkaido specimens of H. calliger; (I) paratype of H. heteropalpis; (J) holotype of H. heteropalpis.

Figure 9. Hygrobates (Hygrobates) foreli. (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, genital field, scale 3. Scale bars: 1, 2, 3 (B, F, G)5100 mm; 3 (D, E)550 mm.

Figure 10. Hygrobates (Hygrobates) foreli, female. (A) First leg; (B) second leg; (C) third leg; (D) fourth leg. Scale bar: 100 mm.

Figure 19. Hygrobates (Hygrobates) sokolowi. (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; (G) genital field, scale 3. (F) Female, genital field, scale 3. Scale bars: 1, 2, 3 (B, F, G)5100 mm; 3 (D, E)550 mm.

Figure 20. Hygrobates (Hygrobates) sokolowi, male. (A) First leg; (B) second leg; (C) third leg; (D) fourth leg. Scale bar: 100 mm.