Hygrobates (Rivobates) zawali, Pešić, Vladimir, 2015

Pešić, Vladimir, 2015, A new species of the water mite genus Hygrobates Koch, 1837 (Acari: Hydrachnidia: Hygrobatidae) from the ancient Lake Ohrid, Zootaxa 3926 (2), pp. 287-295 : 288-289

Hygrobates (Rivobates) zawali n. sp.

( Figs. 1A–E , 3A–D , 4A–D)

Hygrobates diversiporus Stanković, 1931 , nec Sokolow, 1927; K. Viets 1936; Bader 1955; Georgiev 1957; Stanković 1960; Pešić 2003; Baker et al. 2008; Pešić et al. 2010; Dovgal et al. 2012.

Hygrobates quanaticola Esen et al. 2013 : fig. 4, nec Schwoerbel & Sepasgozarian, 1976.

Type series. Holotype male ( MNHP), dissected and slide mounted, Macedonia, Lake Ohrid, 5.viii.1955 coll. Petkovski. Paratypes: 12 females, same data as holotype, two females dissected and slide mounted.

Compared material. Senckenberg Museum Frankfurt, Germany, Hygrobates (Decabates) quanaticola , holotype, ♂, slide J/15, Locality. Quanat near Rezayeh, 29.9.1974 coll. Schwoerbel; slide J/16, Hygrobates (Decabates) quanaticola, Allotyp ♀, Quanat near Rezayeh, 29.9.1974, Schwoerbel; slide J/14, Hygrobates (Decabates) quanaticola , ♀, Quanat near Rezayeh, 29.9.1974, Schwoerbel.

Diagnosis. In both sexes, posterior margin of Cx-I+II medially equally rounded, suture line Cx-III/IV slightly bowed near glandular opening on Cx-IV. Number of Ac low (4–7 pairs, regularly 5–6). Male genital field ovoid, anterior margin convex (with a narrow border of secondary sclerotization), posterior margin irregularly convex. Female gonopore distinctly longer than genital plates (L ratio genital plate/gonopore 0.53–0.55).

Description. Lateral eyes well developed; dorsal and ventrocaudal idiosoma without sclerotized muscle insertions. Coxae in three groups; posterior margin of Cx-I convexly rounded, medial margin of Cx-IV rounded. Genital field with 5–7 pairs of Ac. Palp with fine denticulation on distoventral surfaces of P-2 and –3, P-2 with a bluntly rounded distoventral projection, P-3 distoventrally slightly protruding. P-4 ventral margin slightly projecting near the insertion of two (distanced, 13–19 µm) ventral setae.

Measurements. Male (holotype)—Idiosoma L 720. Coxal field: L/W 322/584 Cx-I+II L/W 225/321; median L of Cx-I + gnathosoma 241; Cx-III W 423. Genital field L/W 139/165; anterior margin convex, with a narrow border of secondary sclerotization, posterior margin irregularly convex, bearing about 14 pairs of setae and 6 pairs of Ac; gonopore L 52.

Palp measurements: total L 393, dL/H, dL/H ratio: P-1, 31/34, 0.91; P-2, 102/65, 1.57; P-3, 71/60, 1.18; P-4, 138/37, 3.7; P-5, 51/17, 2.9; L ratio P-2/P-4, 0.74, P-3/P-4, 0.51. Chelicera total L 281.

Legs: dL of I-L-2–6: 72, 92, 128, 131, 147; II-L-2–6: 78, 101, 131, 156, 165; III-L: 59, 73, 113, 159, 178, 178; IV-L: 131, 109, 169, 222, 238, 213.

Female (paratype, n = 2)—Idiosoma L/W 860–960/745–840. Coxal field: L/W 316–320/588–608; Cx-I+II L/ W 213–217/314–319; median L of Cx-I + gnathosoma 234–239; Cx-III W 438–445. Genital plate L/W 131–135/ 62–63, with a rather long gonopore and moderately developed pre- and postgenital sclerites, genital plates about half the length of the gonopore, situated in posterior half of genital field, laterally convex, medially (just posterior to Ac-1) indented, bearing about 11 pairs of setae and 5–6 pairs of Ac; gonopore L 245–247; L ratio genital plate/ gonopore 0.53–0.55; egg maximum diameter 266–272 (n = 2).

Palp measurements: total L 388–389, dL/H, dL/H ratio: P-1, 30–31/34–37, 0.81–0.92; P-2, 98–103/63–65, 1.5–1.63; P-3, 68/63, 1.1; P-4, 137–142/38–39, 3.56–3.7; P-5, 49–51/18, 2.7–2.9; L ratio P-2/P-4, 0.69–0.75, P-3/ P-4, 0.48–0.49. Chelicera total L 253.

Legs: dL of I-L-2-6: 72–74, 100, 116–134, 116–141, 153; II-L: 56, 67–75, 101–106, 136–141, 153, 166–168; III-L: 58–66, 75–81, 116, 162–163, 181–184, 181–188; IV-L: 115–116, 109–116, 169–170, 226–228, 228–231, 209–216.

Etymology. Named after Andrzej Zawal (Szczecin, Poland) for his contribution to the ecology and taxonomy of water mites of the Lake Ohrid.

Remarks. Populations from Ohrid Lake formerly assigned to Hygrobates diversiporus Sokolow, 1927 , represent a distinct, undescribed species. Males of the former species differ in the reverse heart-shaped genital field with an acute anterior angle and indented posterior margin having a broad, rounded median notch ( Fig. 2E ), females in genital plates being longer than half the gonopore ( Fig. 2F ).

Due to the similar morphology of the genital field in both sexes, the new species is most similar to H. quanaticola . The latter species was originally described from Iran ( Schwoerbel & Sepasgozarian 1976), and later on reported from Turkey ( Erman et al. 2010). Esen et al. (2013) re-examined the holotype and stated that it differs from H. diversiporus in the shape of the male genital field (not indented, but with irregularly convex posterior margin). However, by mistake, Esen et al. (2013) gave an illustration of the genital field of the specimen from the Lake Ohrid which is here described as a new species. Based on the original description and re-examination of the type series, diagnostic characters of H. quanaticola in comparison with H. zawali n. sp. (in parentheses) are: 1) anterior margin of male genital field with a short medial projection (without anterior projection), 2) suture line Cx- III/IV strongly bowed near glandular opening on Cx-IV (slightly bowed); and 3) male gonopore longer, L 72 µm (52 µm). Furthermore, H. quanaticola differs also in minor dimensions of palp segments (L P-2 <100, P-3 <80, P- 4 <130 µm; data taken from the original description).

Variability. Bader (1955) gave a comprehensive study on the variability of the number of acetabula in a population of H. diversiporus from Lake Ohrid (here described as a new species). He found nine different combinations Ac numbers per genital (right+left) plates: the dominant combinations were: 6+5 (27% of the total specimens examined, n = 35) and 6+5 (21.6%), followed by 5+5 (18.9%) and 5+6 (13.5%).

Epibionts. Some specimens were covered by suctorian epibionts, identified as Tokophrya wenzeli Matthes & Stiebler, 1970 . This species is a characteristic epibiont of freshwater mites from lentic waters ( Dovgal et al. 2012).

Habitat. The population in our study collected in summer was strongly female-biased, with only one male in a mature state, suggesting that males hatch earlier than females. We do not know the exact microhabitat or depth at which the specimens were collected. Andrzej Zawal (personal communication) collected this species from 20 to 80 m depth. He stated that most specimens were found in the belt of Chara algae at a depth of 20 meters, slightly less specimens were collected from stony substrata between 20 and 40 meters depth, while the muddy substrata at a depth of 80 meters produced only four specimens. Following Albrecht et al. (2006), the nearly continuous belt of Chara algae impedes the migration of benthic invertebrates. The upper zone of the deep layer (below the termocline at a depth of about 25 m at the end of summer) is characterized by a relatively high oxygen saturation ( Stanković 1960), a factor important for water mites because they do not occur in anoxic waters. Below the 50 m isobath, no benthic photic production is possible ( Stanković 1960).

Distribution. Known only from Lake Ohrid.

Figures

FIGURE 1 A – E. Hygrobates zawali n. sp. (A, C = male holotype, B, D – E = female paratypes): A – B = coxal field; C – E = genital field. Scale bar = 100 µm.

FIGURE 3 A – F. A – D. Hygrobates zawali n. sp. (A, B = male holotype, C – D = female paratype): palp. E – F H. quanaticola Schwoerbel & Sepasgozarian, 1976 (E = male holotype, F = female [slide J / 14]): palp (from Schwoerbel & Sepasgozarian 1976). Scale bar = 100 µm.

FIGURE 2 A – F. A – D Hygrobates quanaticola Schwoerbel & Sepasgozarian, 1976 (A, C = male holotype, B, D = female paratype): A – B = coxal field; C – D = photographs of the genital field. E – F H. diversiporus Sokolow, 1927 (E = male, F = female): genital field (from Sokolow 1927). Scale bar = 100 µm.