Atractides (Atractides) siamis sp. nov.

(Figs. 1A–D, 2A–D)

Type material. Holotype: male dissected and slide mounted in Hoyer's fluid. MALAYSIA, Jerian stream, Fraser’s Hill, 14.ii.2009, 3° 43.479 N 101° 42.935 E, alt. 1011 m, leg. Smit. Paratypes: 1/1/0, same data as holotype; 0/4/0 (0/1/0 mounted), Malaysia, unnamed creek crossing Road 55 to Kuala Kubu Bharu, 8.ii.2009 3° 40.511N 101° 44.511 E, alt. 823 m, leg. Smit.

Further material. MALAYSIA: river Gumut at crossing with road 55, 18.ii.2009, 3° 37.155 N 101° 44.558 E, leg. Smit 1/0/0; stream crossing road to Ringlet, Cameron Highlands, 18.ii.2009, 4° 22.212 N 101° 21.522 E, alt. 1011 m, leg. Smit, 0/2/0; tributary of Tahan River near Lata Berkoh, Taman Negara NP, 9.ii.2009, 4° 26.635 N 102° 23.057 E, alt. 82 m, leg. Smit, 0/1/1. THAILAND: River at km. 13, alt. 465 m, Doi Inthanon NP, 25.xi.2007, 18° 31.532 N 98° 39.091 E, leg. Smit, 1/0/0 (1/0/0 mounted).

Diagnosis. Integument dorsally striated; unsclerotized dorsal muscle attachments; weak sexual dimorphism of P-2, sword seta of P-4 proximally from the proximoventral hair; I-Leg-5 elongated with a rather homoimorphic S-1 and S-2 with a short setal interspace; I-Leg-6 rather short, curved and distally tapering.

Description. General features. Integument dorsally striated. Muscle attachment plates unsclerotized. Genital field: Ac in triangular arrangement; excretory pore smooth; Vgl-1 separated from Vgl-2. Palp: P-2 ventral margin straight, P-4 maximum H near the proximal hair insertion, proximoventral hair near a pointed denticle, sword seta of P-4 proximally from the proximoventral hair. I-Leg: I-Leg-5 elongated, with dorsal and ventral margins only weakly diverging distally, short setal interspace of S-1 and S-2, and these setae similar in dimensions, stocky, bluntly pointed, S-2 thicker than S-1; I-Leg-6 short, curved, basally thickened, distally tapering.

Male (holotype; in parentheses specimen from River at km. 13, Thailand). Idiosoma L/W 297-303 (353)/ 219-234 (253). Coxal field (Fig. 1A): L 192 (208), Cx-3 W 220 (238), Cx-1+2 mL 88 (81), Cx-1+2 lL 139 (138). Palp (Figs. 1 B-C): total L 164 (172), dL: P-1 18 (18), P-2 35 (39), P-3 40 (43), P-4 49 (50), P-5 22 (22); %L: P-1 11.0 (10.5), P-2 21.3 (22.7), P-3 24.4 (25.0), P-4 30.0 (29.1), P-5 13.4 (12.8); L P-2/P-4 0.72 (0.78).

Genital field (Fig. 1A): anterior margin convex, posterior margin deeply indented, L/W 61 (70)/ 65 (71), L Ac-1-3: 21 (21)-22 (23)-25 (30).

I-Leg (Fig. 1D): I-Leg-5 dL 89 (89), vL 73 (76), dL/vL 1.22 (1.18), HB 28 (29), dL/HB 3.18 (3.1), S-1 L 41 (41), L/ W 13.7 (8.9), S-2 L 42 (44), L/ W 6.2 (6.3), distance of sword setae at I-Leg-5 3 (2), L S-1/2 0.97 (0.93); I-Leg-6 L 52 (55), HB 12 (12), L/HB 4.3 (4.5); L I-Leg-5/6 1.73 (1.64).

Female (from unnamed creek crossing Road 55 to Kuala Kubu Bharu, Malaysia). Idiosoma L/W 444/325. Coxal field (Fig. 2A): L 225, Cx-3 W 281, Cx-1+2 mL 91, Cx-1+2 lL 153. Palp (Fig. 2D): total L 199, dL and %L (in parentheses): P-1 21 (10.6), P-2 43 (21.6), P-3 53 (26.6), P-4 58 (29.2), P-5 24 (12.1); L P-2/P-4 0.74. Genital field (Fig. 2B): L/W 127/102, genital plate L 67, L Ac-1-3: 22-21-22.

I-Leg (Fig. 2C): I-Leg-5 dL 110, vL 92, dL/vL 1.2, HB 31, dL/HB 3.6, S-1 L 47, L/ W 10.2, S-2 L 50, L/ W 5.5, distance of sword setae at I-Leg-5 4, L S-1/2 0.94; I-Leg-6 L 59, HB 13, L/HB 4.5; L I-Leg-5/6 1.86.

Remarks. The new species can easily be distinguished from the other Indo-Malayan members of the genus Atractides in the combination of a striated integument, unsclerotized dorsal muscle attachment plates, a weak sexual dimorphism of P-2, sword seta of P-4 proximally from the proximoventral hair, elongated I-Leg- 5 with a rather homoimorphic S-1 and -2 and a narrow setal interspace, and a rather short, curved and distally tapering I-Leg-6.

Within the Palaearctic fauna, due to the striated integument, unsclerotized dorsal muscle attachments plates, a rather short, curved and distally tapering I-Leg-6, unfused Vgl-1 and -2, a smooth excretory pore and a palp with weak sexual dimorphism, Atractides siamis sp. nov. is most similar to A. vaginalis (Koenike, 1905), a crenobiontic species known from the Alps and Tatras (Gerecke 2003), from which it can be easily distinguished in a sword seta of P-4 situated proximally from the proximoventral hair (near distoventral hair in A. vaginalis).

Etymology. The species is named after Siam.

Distribution. Malaysia, Thailand.