Atractides (s. str.) pollux, Gerecke, 2021

Gerecke, Reinhard, 2021, The water mites of the family Hygrobatidae (Acari, Hydrachnidia) in Italy, Zootaxa 5009 (1), pp. 1-85 : 35-37

Atractides (s. str.) pollux sp. nov.

(Figs 17-18; 30 P-Q; 31 W-X)

Type series: Holotype ♂, SMF: Sicilia: I 468, Sicilia (PA), Sicani; Giuliana, spring Torrente Landro , 670 m, UTM UB 422 735, 24.08.1986, slide; paratypes: same site and date, 1/1/0 slide ( NHMW); 0/1/0 slide, 1/9/0 in liquid; interstitial dig 0/1/0 slide; I 469, same site and date, spring stream, 660 m, 2/2/0 slide; I 477, same site, 05.09.1986, 1/0/0 slide ( SMF).

Further material: Calabria: I 106, 0/1/0 slide; I 435, 0/1/0; I 1108, 0/1/0 slide; I 1137, 0/3/1 (0/1/0 slide); Lazio: I 880, 0/1/0 slide; I 886, 1/3/0 (1/1/0 slide); Sicilia: I 1, 0/1/0 slide; I 56, 1/1/3 (1/2/3 slide); I 60, 1/2/1 (1/0/1 slide); I 68, 0/1/0 slide; I 98, 0/2/1 (0/1/1 slide); I 100, 2/1/1 slide; I 134 1/0/0 slide; I 137, 1/0/0 slide; I 167, 0/1/0 slide; I 179, 3/1/0 slide; I 183, 1/0/0 slide; I 187, 0/1/1 slide; I 199, 11/6/5 (6/4/1 slide); I 205, 11/4/1 (1/2/1 slide); I 207, 3/2/0 (1/1/0 slide); I 211, 1/1/0 slide; I 212, 0/2/0 (0/1/0 slide); I 213, 1/1/0 slide; I 221, 2/1/0 (1/1/0 slide); I 234, 2/0/0 (1/0/0 slide); I 250, 5/10/0 (2/0/0 slide); I 277, 0/1/0 slide; I 303, 0/1/0 slide; I 308, 0/1/0 slide; I 470, 0/1/0 slide; I 481, 4/1/0 slide; I 497, 3/1/3 slide; I 498, 1/1/0 slide; I 500, 4/2/0 slide; I 502, 2/3/0 slide; I 503, 2/0/0; I 517, 0/1/0 slide; I 519, 1/1/0 slide; I 544 Int, 1/1/0 slide; I 552, 0/1/1 slide; I 578, 0/1/0 slide; I 587, 0/1/0 slide; I 598, 0/1/0 slide; I 599, 1/13/0 (1/1/0 slide); I 616, 1/0/0 slide; I 659, 2/3/0; I 661, 1/0/0 slide; I 662, 0/1/0 slide; I 667, 1/0/0 slide; I 1078 a, 0/1/0; I dp 32, 0/1/0 slide; I dp 34, 1/2/1 slide; I dp 55, 0/1/0 slide; I dp 66, 1/0/0 slide; I dp 67, 1/1/1; I dp 84, 0/2/0 slide; I dp 133, 1/0/0 slide. 57 sites, 207 specimens.

Diagnosis: Integument lineated; muscle insertions and excretory pore smooth; Vgl-1/2 separate. Genital field with Ac in a weakly curved line (Figs 17 B, 18 B). I-L-5 dorsal and ventral margins diverging from base to insertion of S-1, in males gradually (Fig. 17 A), in females more strongly (Fig. 18 C), to form a prominent extension at distoventral edge; S-1-2 distanced, S-1 curved, with concave adaxial margin, apically truncated and with a fine distomedial extension. I-L-6 curved. P-3 ventral margin in distal half hyaline; P-4 maximum H on the level of proximoventral seta, sword seta near distoventral seta. Males: Genital field (Fig. 17 B) anterior margin straight, posterior margin medially concave. P-2 ventral margin equally rounded (Fig. 17 C). Females: P-2 ventral margin straight to very weakly convex, ventrodistal angle acute (Fig. 18 A).

Fig. 17: Atractides pollux sp. nov., type series (I 468), ♂. A, I-L-5/6; B, genital field; C, palp medial; D, venter. Scale bars: 100 µm.

Fig. 18: Atractides pollux sp. nov., paratype ♀ (I 468). A, palp medial; B, genital field; C, I-L-5/6. Scale bar: 100 µm.

Description: Integument strongly lineated; lateral eyes well developed and pigmented; dorsal and posteroventral muscle insertions, as well as anal pore, smooth; glandularia not extended, diameter about 25. Vgl-1+2 separate from each other by an extended membranous area. Coxal plates in three groups. Posterior margin of Cx-I+II irregular, with a prominent posteromedial extension, posterior apodemes of Cx-I proximally forming an acute angle, in distal part curved. Proportions of I-L and palps with sexual dimorphism. I-L-5 dorsal and ventral margins diverging from base to insertion of S-1; distance S-1-2 wide, S-1 curved, with concave adaxial margin at distal edge ending in a very fine extension, apically truncated; S-2 stout, in distal part equally narrowed, with a rounded tip. I-L-6 curved, in basal part distinctly thicker than distally. Gnathosoma with a short rostrum, chelicera normal in proportions (L/H 4.8-5.8, basal segment/claw ratio 2.1-2.6).

Males (n = 15): Idiosoma L/W 500-650/370-500; coxal field L/Cx-III W 290-360/330-460, Cx-I+II mL 90-110, lL 190-240, W 260-330 (mL/W ratio 0.28-0,35). Genital field L/W 88-104/100-120, ratio 0.82-0.94, with about 25 pairs of setae; Ac-1-3 maximum diameter 24-32, 24-38, 24-34, gonopore L 60-65; anterior margin straight, posterior margin medially concave. I-L with segments 3 and 4 forming broadly protruding, rounded distal sheaths covering the base of the subsequent segment. I-L-5 dL/vL 180-214/116-132, ratio 1.54-1.66, dorsal and ventral margins equally diverging from the base to S-1 insertion, ventral seta at 17-31 % of vL); HA 50-63, HB 56-68, HC 103-125, ratio dL/HB 2.8-3.3. L (L/W) S-1, 103-125 (10.3-12.6), S-2, 75-90 (5.5-7.8), distance S-1-2, 24-36, ratio S-1 L/distance S-1-2, 1.2-1.5. I-L-6 L 140-172, HA 23-29, HB 18-23, HC 19-23, ratio L/HB 7.1-8.6; ratio I-L-5 dL/I-L-6 L 1.2-1.3. Palp rather stout, total L 300-353; proportions of segments (L/H, ratio, % total L): P-1, 30-38/29-33, 1.0-1.2, 10- 11; P-2, 70-83/50-60, 1.17-1.40, 21-24; P-3, 65-85/45-55, 1.3-1.6, 21-24; P-4, 98-115/35-43, 2.5-2.9, 32-33; P-5, 31-38/10-13, 2.5-3.5, 10-12; L ratio P-2/P-3, 0.88-1.08, P-2/P-4, 0.64-0.75; P-3/P-4, 0.65-0.74. P-2 ventral margin equally convex, without projection; P-3 ventral margin straight, in distal half hyaline. P-4 with sword seta position producing a distance to proximal/distal edge ratio of 1.5-2.1); seta insertions dividing margin into two subequal and one shorter sector(s) (relative length in %: 32-42/32-44/21-27).

Females (n = 8): Idiosoma L/W 560-950/420-800; coxal field L/Cx-III W 380-430/430-560, Cx-I+II mL 115- 130, lL 240-270, W 360-390 (mL/W ratio 0.31-0.46). Genital field L 150-190, with bean-shaped acetabular plates (L/W 116-136/36-50, ratio 2.6-3.3); Ac-1-3 maximum diameter 34-36, 32-44, 32-38, pregenital sclerite small, with short lateral extensions. I-L-3/-4 not forming distal sheaths. I-L-5 more inflated than in males, dL/vL 244-280/136- 160, ratio 1.72-1.85, dorsal and ventral margins strongly diverging from the base to S-1 insertion, ventral seta close to S-1 (distance to distoventral edge 12 - 20 % vL); HA 78-90, HB 83-98, HC 115-128, ratio dL/HB 2.7-3.0. L (L/W) S-1, 148-165 (10.7-15.8), S-2, 108-120 (5.6-6.9), distance S-1-2, 45-60, ratio S-1 L/distance S-1-2, 2.7-3.3. I-L-6 L 216-252, HA 28-33, HB 16-20, HC 20-25, ratio L/HB 10.8-14.4; ratio I-L-5 dL/ I-L-6 L 1.1-1.24. Palp slenderer than in males, total L 398-433; proportions of segments (L/H, ratio, % total L): P-1, 35-43/33-38, 1.0-1.3, 9-10; P-2, 85-93/60-63, 1.4-1.5, 21-23; P-3, 110-125/50-55, 2.1-2.4, 27-29; P-4, 118-133/33-38, 3.3-3.9, 30-31; P-5, 38-43/13-15, 2.8-3.2, 9-11; L ratio P-2/P-3, 0.74-0.82, P-2/P-4, 0.70-0.74; P-3/P-4, 0.88-0.98. P-2 ventral margin straight, distal edge forming an acute angle; P-3 ventral margin straight, hyaline portion in distal half well visible. P- 4 sword seta insertion: ratio distance to proximal/distal edge 1.4-2.3; ventral setae insertions dividing ventral margin into two shorter proximal (28-33 %) and distal (23-31 %) sectors flanking a larger central one (38-45 %).

Derivatio nominis: Like Pollux with Castor, two sons of Leda, also Atractides pollux is in a sibling relationship with A. castor .

Discussion: Atractides pollux is similar to A. castor and A. allgaier in the combination of a lineated dorsal integument, smooth muscle insertions and excretory pore, and a I-L with enlarged penultimate segment bearing a truncated sword seta S-1. Both species (in parentheses) differ in shape of seta S-1 (less curved, apical part much more broadened) and in generally minor dimensions (e.g., palp total L ♂♂ <280, ♀♀ <350, I-L-5 dL ♂♂ <170, ♀♀ <220). Females of the new species differ from A. allgaier in the slenderer I-L-5 ( A. allgaier dL/HB ratio 3.0- 3.2), from A. castor in the relatively longer ventral margin ( A. castor dL/vL ratio 2.0-2.3). In a female from I 56, the integument lineation is very dense, grading into the situation of a striated integument. Measurements of males from I 199 tend to grade into the variability of A. fluviatilis .

Habitat: Rhithrobiont, crenophilous; in springs of various typology and streams of various order, at 20-1350 m; one record from hyporheic interstitial (I 544 Int).

Distribution: Central and Southern Italy, obviously rather frequent.