Atractides (Atractides) glandulosus Walter, 1918

Smit, Harry, Gerecke, Reinhard, Pešić, Vladimir & Gledhill, Terence, 2015, On the taxonomic state of water mite taxa (Acari: Hydrachnidia) described from the Palaearctic, part 3, Hygrobatoidea and Arrenuroidea with new faunistic data, Zootaxa 3981 (4), pp. 542-552 : 544-546

Atractides (Atractides) glandulosus Walter, 1918

( Figs 1–2 )

Material examined. Germany D 700, Baden-Württemberg, Laimnau (FN), stream Argen near influence Bollenbach, 432 m, 47°38'3.00"N, 9°37'44.13"E, Gerecke coll. 10-VIII-2014 (6/1/0).

Both sexes: Integument completely smooth or with a very fine striation. Lateral eyes with large pigment dots. Dorsal and posteroventral muscle attachments unsclerotized, but glandular sclerites enlarged (Dgl-3/-4 diameter 30–40 µm). Coxae in three groups, but anterior margins of Cx-III closely adpressed to posterolateral margins of Cx-II. Legs without swimming setae, leg claws pointed, with apically rounded internal clawlet and narrow claw blade. I-L-4 forming enlarged distomedial and -lateral sheaths embracing base of I-L-5. I-L-5 with diverging dorsal and ventral margins, in the area of S-1/-2 insertion rather wide (ratio dL/HB 2.6–3.0), ventral margin slightly concave. Setae S-1/-2 strong, heteromorphic, S-1 slightly curved and slender (maximum W near base), apically truncated and with a fine adaxial denticle; S-2 shorter (L ratio S-1/-2, 1.2–1.3) and distinctly larger, dagger-shaped. I-L-6 stout (L/HB ratio 4.9–6.0) and curved, dorsal and ventral margins converging in proximal part, subparallel distally; L ratio I-L-5/6 1.40–1.56. Excretory pore without sclerotization, Vgl-1 separate from Vgl-2. Palp with a strong and long sword seta on P-4, shape of segments with sexual dimorphism.

Male: Setae of dorsal glandularia very long, in particular those of Dgl-3 and -4 (up to 125 µm). Vgl-3 fused to posterior margin of Cx-IV. I-L-6 particularly stout. Genital plate with straight or slightly convex anterior margin, posterior margin medially indented in an obtuse angle. Gonopore long, flanked by 9–10 pairs of fine setae; about 15 further pairs of fine setae at lateral and posterior genital plate margins. Acetabula relatively large, subtriangular; Ac-3 rather long and with their anterior edge approaching to posterior edge of Ac-1. Palp with a rounded, in some individuals slightly bipartite or rugose distoventral projection at P-2, P-4 stout, with a dense cover of fine dorsal setae, maximum H on the level of a blunt protrusion of the ventral margin flanking the insertion of the proximoventral seta; sword seta very strong and long, inserting slightly anterior to proximoventral seta.

Measurements (n = 6): Idiosoma: L/W 490–550/400–430; coxal field L 285–325, Cx-III W 330–365, L/W ratio 0.85–0.95; Cx-I+II mL 113–126, lL 198–221, W 260–270, mL/W ratio 0.42–0.48. Genital field L/W 99–108/ 122–135, ratio 0.76–0.89; L Ac 1–3: 34–40, 29–43, 43–47; ejaculatory complex L about 100. I-L: I-L-5 dL 159– 175, vL 121–134, dL/vL ratio 1.30–1.36, HA 47–56, HB 56–65, HC 58–67; ratio dL/HB 2.6–2.8; S-1 L 83–89, L/ W 8.1–10.9; S-2 L 67–75, L/W 5.8–7.5, distance S-1-2, 16–18; L ratio S-1/2, 1.2–1.3; I-L-6 L 106–122, HA 29– 32, HB 21–23, HC 20–22; L/HB ratio 4.9–5.6; L ratio I-L-5/6, 1.4–1.5.

Gnathosoma: Gnathosomal base vL 100–125; chelicera total L 193–208, ratio L/H 5.1–5.8, L ratio basal segment/claw 2.0–2.1. Palp: total L 256–281, L/H (ratio L/H; rel. L): P-1, 24–29/24–28 (0,9–1,1; 9–10); P-2, 59– 66/46–54 (1.2–1.3; 22–24); P-3, 64–69/36–43 (1.6–1.8; 24–25); P-4, 81–87/35–39 (2,2–2.4; 31–32); P-5, 29–31/ 12–13 (2.3–2.6; 11); L ratio P-2/P-4, 0.68–0.76; position of sword seta (ratio distance to proximal/distal segment edge) 0.9–1.2; ventral segment sectors (distance proximal segment edge-proximoventral seta/proximoventraldistoventral seta/distoventral seta-distoventral segment edge, % total ventral L): 36–36/28–36/26–28.

Female: Dorsal setae shorter and more slender, in the obviously newly hatched specimen Vgl-3 distanced from posterior marging of Cx-IV. I-L-6 slightly more slender than in males. Genital field with rather short gonopore, pregenital sclerite small, with rounded lateral margins. Genital plates nearly semicircular, medial margins equally slightly concave, lateral margins strongly rounded, each plate bearing 11 fine setae; Ac large, subtriangular, Ac-3 with rounded posterior margin. Palp with unmodified, slightly convex ventral margin of P-2, P-4 slender, maximum H in distal part, ventral margin very slightly protruding near proximoventral seta, sword seta strong, and long, inserted halfway between proximal setae.

Measurements (n = 1): Idiosoma L/W 775/ 620; coxal field L 340, Cx III W 390, L/W ratio 0.9; Cx-I+II mL 135, lL 243, W 324, mL/W ratio 0.42. Genital plate L/W 108/50, L Ac 1-3: 45, 40, 45. I-L: I-L-5 dL 220,, vL 159, dL/vL ratio 1.38, HA 63, HB 74, HC 78, dL/HB ratio 3.0, S-1 L/W 110/10, ratio 11.0, S-2 L/W 92/14, ratio 6.7, distance S-1-2, 25, L ratio S-1/2, 1.2; I-L-6 L 140, HA 33, HB 23, HC 23, L/HB ratio 6.1; L ratio I-L-5/6, 1.56.

Gnathosoma: Gnathosomal base vL 137; chelicera total L 264, ratio L/H 5.9; L ratio basal segment/claw 1.95. Palp total L 325, L/H (ratio L/H; rel. L): P-1, 29/29 (1.0; 9); P-2, 64/52 (1.2; 20); P-3, 92/43 (2.2; 28); P-4, 104/30 (3.5; 32); P-5, 37/15 (2.5; 11); L ratio P-2/P-4, 0.62; position of sword seta (ratio distance to proximal/distal segment edge) 1.1; ventral segment sectors (distance proximal segment edge-proximoventral seta/proximoventraldistoventral seta/distoventral seta-distoventral segment edge, % total ventral L): 33/33/33.

Remarks. Due to the poor original description and uncertain attribution of females, the definition of this species remained problematic until present day ( Gerecke 2003). Atractides glandulosus was at first described from a Swiss affluent of Lake Constance, the Aare, and later reported by Walter (1944, with the first figures, and the first description of the female) from streams in Austria. Following Lundblad (1956), the only author who gave additional morphological information, A. glandulosus is a rare species distributed also in streams draining the SW German Black Forest and the French Pyrenees.

Both sexes of Atractides glandulosus are characterized by the combination of a smooth integument, the name giving extended glandular sclerites and enlarged terminal I-L segments (with the particular characteristics of the truncate S-1 bearing an adaxial denticle, and the proximally thickened I-L-6). In this character combination, A. glandulosus differs from all other known Atractides species which have in common (1) a postgenital area with unsclerotized excretory pore and unfused Vgl-1/2, (2) a genital field bearing large acetabula, with an unindented anterior margin in males and halfcircle-shaped genital plates in females, and (3) palps with a distinct sexual dimorphism, but without a pointed distoventral extension of P- 2 in males. The attribution of the single female found together with the males is ascertained by the important features of the integument, shape of I-L-5/-6 and postgenital field found in both sexes.

The detection of an additional population, again from an affluent of Lake Constance allows two statements: (1) the attribution of females and males as proposed by Lundblad (1956) is obviously correct, while a female specimen from the type locality (erroneously labeled as “ type ”) represents another, unclear Atractides species (see Gerecke 2003); (2) the proposal of Gerecke (2003), to consider A. glandulosus a crenobiont, finds no support. It is a character species of larger streams with stony and gravel substrata typically formed in the premontane areas.

Figures

FIGURE 1. Atractides glandulosus male from river Argen; a, I-L- 5 / 6; b, palp; c, dorsum, partial view; d, venter. Scale bars = 100 µm.

FIGURE 2. Atractides glandulosus female from river Argen; a, palp; b, genital field; c, I-L- 5 / 6 (detail: shape of setae S- 1 / 2). Scale bar = 100 µm.