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

Gerecke, Reinhard, 2021, The water mites of the family Hygrobatidae (Acari, Hydrachnidia) in Italy, Zootaxa 5009 (1), pp. 1-85 : 13-15

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

(Figs 6-7; 31 U-V)

Type series: Holotype ♂, SMF, Sicilia: I 652, Nebrodi ( ME), Caronia, spring near Case Crocitti , 850 m, UTM VC 489 018, 24.06.1988, slide . Paratypes: same site and date, 1/1/0 slide ( NHMW); 0/1/0 slide, 7/13/0 in liquid ( SMF) .

Further material: Calabria: I 1064 b, 3/14/0 (3/3/0 slide); I 1103, 1/2/0 (1/1/0 slide); I 1104, 1/0/0 slide; I 1106, 0/1/0 slide; I 1107, 4/15/0 (2/2/0 slide); I 1110, 2/4/0 (1/1/0 slide); I 1126, 10/12/0 (1/2/0 slide); I 1127 b, 5/6/0 (1/1/0 slide); I 1130, 1/2/1; I 1131, 6/20/0 (1/1/0 slide); I 1134, 3/2/0; I TG 18-03a, 0/1/0; Sardegna: I TG 15-03, 1/1/1 slide; Sicilia: Etna, Nebrodi, Peloritani; I 59, 0/1/0 slide; I 517, 3/0/0 slide; 531, 3/0/0 (1/0/0 slide); I 545, 0/2/0 (0/1/0 slide); I 568, 1/0/0 slide; I 594, 2/0/0 (1/0/0 slide); I 596, 0/2/0 (0/1/0 slide); I 605, 1/0/0 slide; I 617, 0/2/0 slide; I 627, 0/1/0 slide; I 628, 1/1/0 (1/0/0 slide); I 642, 0/1/0 slide; I 647, 0/2/0 slide; I 652, 9/15/0 (2/2/0 slide); I 657, 1/0/0 slide. 27 sites, 169 specimens.

Previous records, published under the name of A. allgaier (see Gerecke 2014b): Corsica: F 35, 1/0/0; F 79, 0/3/0; F 83b, 1/5/0; F 84, 3/3/0. Sardegna: I 1155, 1/0/0; I 1159, 0/1/0; I 1160, 1/0/0; I 1162, 1/0/0; I 1172, 1/0/0.

Diagnosis: Dorsal integument lineated; muscle insertions and excretory pore, smooth; Vgl-1+2 close to each other, often fused, but occasionally separate as a matter of individual variability (Fig. 6 C). Genital field with Ac in a weakly curved line (Figs 6 D, 7 C). Proportions of I-L (Figs 6 A, 7 A) and palps (Figs 6 B, 7 B) with weakly developed sexual dimorphism. I-L-5 distinctly enlarged near insertion of S-1, distance S-1-2 wide, S-1 long and slender, apically enlarged and truncated, the adaxial margin in central part weakly protruding, at distal edge forming an obtuse extension; S-2 with an obliquely truncated tip. I-L-6 curved, with subparallel dorsal and ventral margins. P-4 maximum H on the level of proximoventral seta, sword seta near distoventral seta. Males: Genital field anterior margin convex, posterior margin slightly concave (Fig. 6 C-D). Palp stout, P-2 ventral margin distally forming an obtuse angle (Fig. 6 B). Females: Palp slenderer than in male, P-2 ventral margin straight to very weakly convex, ventrodistal angle acute (Fig. 7 B).

Description: Dorsal integument strongly lineated; lateral eyes well developed and pigmented; dorsal and posteroventral muscle insertions, as well as excretory pore, smooth; glandularia not extended, diameter about 25. Vgl-1+2 close to each other, generally in touch, in mature specimens often fused (individual variability: frequently fused on one side, but separate on the other). Coxal plates in three groups. Posterior margin of Cx-I+II broadly convex, posterior apodemes of Cx-I forming an obtuse angle. I-L-5 distinctly enlarged near insertion of S-1, ventral seta close to distoventral edge (distal L 8-14 % total L); distance S-1-2 wide, S-1 apically widened and truncated, the adaxial side weakly protruding in central part and forming an obtuse extension at distal edge; S-2 distinctly stouter, maximum width in basal third, with an obliquely truncated tip. I-L-6 curved, proximally only slightly thicker than in the centre and apically. Genital field with Ac in a weakly curved line. Gnathosoma with short rostrum, chelicera normal in proportions (L/H 4.7-5.5, basal segment/claw ratio 2.1-2.6). P-4 maximum H on the level of proximoventral seta, sword seta near distoventral seta; seta insertions dividing margin into two subequal and one shorter sector(s) (relative length in %: 23-42/31-54/13-23).

Fig. 6: Atractides castor sp. nov., type series ♂ (I 652). A, I-L-5/6; B, palp; C, venter; D, genital field. Scale bars: 100 µm.

Males (n = 10): Idiosoma L/W 400-500/300-400; coxal field L/Cx-III W 240-270/270-300, Cx-I+II mL 70-90, lL 160-180, W 210-240 (mL/W ratio 0.30-0,40). Genital field broadly rounded (L/W 72-90/80-102, ratio 0.85-0.95) with about 15 pairs of setae; Ac-1-3 maximum diameter 16-28, 19-28, 14-24, gonopore L 45-55; anterior margin weakly convex, posterior margin very weakly 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 144-168/80-92, ratio 1.65-1.91, dorsal and ventral margins equally diverging from the base to S-1 insertion, ventral seta near S-1 (distance to distoventral edge 14 to 29 % vL); HA 40-50, HB 45-54, HC 68-80, ratio dL/HB 2.9-3.4. L (L/W) S-1, 90-108 (10.3-12.3), S-2, 63-73 (5.8-7.7), distance S-1-2, 28-43, ratio S-1 L/distance S-1-2, 1.4-1.5. I-L-6 L 122-152, HA 19-23, HB 16-18, HC 15-18, ratio L/HB 7.2-8.6; ratio I-L-5 dL/I-L-6 L 1.1-1.2. Palp rather stout, total L 225-261; proportions of segments (L/H, ratio, % total L): P-1, 24-28/21-25, 1.0-1.2, 10-12; P-2, 50-58/43-48, 1.15-1.35, 22-24; P-3, 45-60/34-38, 1.2-1.7, 19-23; P-4, 76-88/29-36, 2.2-3.0, 33-35; P-5, 25-30/9-13, 1.0-3.0, 11-12; L ratio P-2/P-3, 0.96-1.22, P-2/P-4, 0.63-0.72; P-3/P-4, 0.55-0.69. P-2 ventral margin projecting in distal part to form an obtuse angle; P-3 ventral margin nearly straight, P-4 maximum H on the level of proximoventral seta, position of sword seta in distal part, but rather variable (ratio distance to proximal/distal edge 1.8-3.0).

Females (n = 11): Idiosoma L/W 490-700/370-530; coxal field L/Cx-III W 275-310/320-385, Cx-I+II mL 80- 100, lL 180-210, W 260-340 (mL/W ratio 0.24-0,40). Genital field (L 120-180) with bean-shaped acetabular plates (L/W 84-100/24-34, ratio 2.8-3.7); Ac-1-3 maximum diameter 16-32, 14-34, 20-28, pregenital sclerite a slender Napoleon-hat shape. I-L-3/-4 not forming distal sheaths. I-L-5 more inflated than in males, dL/vL 192-212/88-104, ratio 2.00-2.27, dorsal and ventral margins equally diverging from the base to S-1 insertion, ventral seta very close to S-1 (distance to distoventral edge 8 to 14 % vL); HA 60-70, HB 65-74, HC 108-120, ratio dL/HB 2.8-3.2. L (L/W) S-1, 133-148 (11.6-14.0), S-2, 83-93 (5.2-7.4), distance S-1-2, 58-63, ratio S-1 L/distance S-1-2, 1.4-1.7. I-L-6 L 184-196, HA 20-24, HB 15-21, HC 15-20, ratio L/HB 9.2-12.5; ratio I-L-5 dL/ I-L-6 L 1.0-1.2. Palp slenderer than in males, total L 270-300; proportions of segments (L/H, ratio, % total L): P-1, 25-33/25-30, 0.9-1.2, 9-12; P-2, 55-68/45-48, 1.2-1.4, 20-23; P-3, 63-73/35-38, 1.8-2.0, 23-24; P-4, 90-103/25-29, 3.2-3.6, 32-34; P-5, 28-34/10-14, 2.1-3.3, 10-11; L ratio P-2/P-3, 0.83-0.96, P-2/P-4, 0.60-0.71; P-3/P-4, 0.69-0.76. P-2 ventral margin straight, but forming a rounded distal edge; P-3 ventral margin straight, P-4 sword seta insertion: ratio distance to proximal/distal edge 2.3-3.3.

Derivatio nominis: See below, under Atractides pollux sp. nov.

Remarks: Atractides castor is similar to A. allgaier in the combination of a lineated integument, smooth muscle insertions and excretory pore, and I-L with enlarged penultimate segment bearing an apically strongly broadened sword seta S-1. Atractides allgaier (in parentheses) differs from the new species mostly in two aspects: (1) different proportions of the terminal segments of I-L, with I-L-5 shorter (dL in males 132-145, in females 178-188), but having a relatively longer ventral margin (ratio dL/vL in males 1.45-1.63, in females about 1.8) and sword setae more close to each other (S- 1-2 in males 17-25, in females 42-47); (2) palp segments generally more slender, segment P-3 relatively longer (L/H ratio P- 3 in females 2.1, in males 1.7; P-3 rel. L 24-25 %, P-3/P-4 ratio in males 0.73, in females 0.78). Male A. allgaier are furthermore clearly distinguished by the absence of a distoventral projection of P-2. Furthermore, a fusion of Vgl-1+2, frequently found in males and females of the new species, has never been observed in A. allgaier .

Under the last point of view, specimens from Corsica and Sardinia are characteristic in having Vgl-1/2 always separate. Instead, they agree in the variability of most measurements and proportions of idiosoma sclerites and appendages.

Habitat: Crenobiont. In shadowed rheohelocrenes at medium and higher altitude (430 to 1500 m); at two occasions, single finds in low order streams (I 1104, I 627).

Distribution: Calabria, Pollino and neighbouring mountains; Sicily (here restricted to the north-eastern mountains); Corsica and Sardinia.

Fig. 7: Atractides castor sp. nov., paratype ♀ (I 652). A, I-L-5/6; B, palp; C, genital field. Scale bar: 100 µm.