Litarachna gracilis sp. nov.

(Figs. 2E–F, 4A–F)

Type series. Holotype female (NIBRIV0000268890), dissected and slide mounted in Hoyer's fluid, South Korea, East Sea, Gangneung beach, sample #5, 37º47.824' N, 128º 55.085' E, 29.iii.2013 Karanović. Paratypes: two deutonymphs, same data as holotype, one deutonymph dissected and slide mounted (NIBRIV0000268891); one female, East Sea, Sokcho, beach, interstitial, 38º09.543' N, 128º 36.554' E, 17.iv.2013 Karanović, fixed in Koenike fluid (MNHP).

Diagnosis: Ocular pigment absent; medial posterior apodemes of Cx-IV reduced to a small knob-shaped hump; P-2 with a tubercle; P-4 ventral tubercle well developed and projecting, dividing segment into two parts, the proximal part longer than distal part, both parts with a concave ventral margin, ventral hair-like setae approaching the distoventral edge of the segment.

Description. Female (holotype): Integument soft, ocular pigment absent (Figs. 2E–F). Idiosoma L/W 397/254. Coxal field: L/W 145/200; Cx-I separated medially; suture lines Cx-II/III and Cx-III/IV incomplete; posterior margin of Cx-IV with medial pairs of apodemes reduced to small knob-shaped hump and the lateral ones short and broad (Fig. 4A). Genital field L/W 80/23, gonopore elongated, pregenital and postgenital sclerite small (L 22–23).

Glandularium-like structure fused with the fourth coxal plates; a pair of small platelets with coxoglandularia 4 and associated setae free in the integument, near the posterior apodemes of Cx-IV. Posterior to the genital field three pairs of wheel-like acetabula (sensu Cook 1996); the anterior one positioned on the level of postgenital sclerite, two posterior pairs, accompanied by a seta, almost touching each other but not fused to a common platelet on their respective sides. Excretory pore unsclerotized. Gnathosoma vL 101; chelicera total L 117–119, claw L 27–29, basal segment L 102–104, L ratio basal segment/claw 3.65–3.7. Palp (Fig. 4C) total L 254, dL dL/H ratio: P-1, 17/ 24, 0.71; P-2, 71/39, 1.8; P-3, 40/34, 1.2; P-4, 97/27, 3.6; P-5, 29/12, 2.4; dL P-2/P-4 ratio 0.73; P-2 with a tubercle, distinctly set up from teh ventral segment margin; P-4 ventral tubercle well developed, dividing segment into two parts, the proximal one longer than distal one, both with a concave ventral margin, ventral hair-like setae approaching the distoventral edge of the segment. Legs: dL of I-L (Fig. 4D): 39, 43, 49, 55, 72, 83; I-L-6 H 23.5, I- L-6 dL/H ratio 3.5; dL of IV-L-3–6 (Fig. 4E): 49, 69, 86, 78; III-L-5 with one swimming seta; IV-Leg-5 with one swimming seta.

Deutonymph: As in adults but lacking a genital field (Fig. 3B). Idiosoma L/W 335/214. Coxal field L/W 101/ 162. Gnathosoma vL 85; chelicera total L 86. Palp (Fig. 4F) total L 191–194, dL/H, L/H ratio: P-1, 14/19, 0.76; P- 2, 55/26, 2.1; P-3, 29/23, 1.29; P-4, 68-71/19, 3.8; P-5, 25/11, 2.3; dL P-2/P-4 ratio 0.78–0.81; dL of I-L: 25, 31, 34, 39, 52, 62; I-L-6 H 18, I-L-6 dL/H ratio 3.5; number of swimming setae as in female.

Etymology. From the Latin adjective gracilis meaning slender; refers to the elongated idiosoma of the new species.

Remarks. Due to the combination of a particularly elongated female gonopore and a projection on P-2 and P- 4, the new species is most similar to Litarachna kamui Uchida, 1935, a species from the Japan Sea were its was collected in plankton or attached to sea-weeds (Uchida 1935). Litarachna kamui can be distinguished from the new species by having developed medial posterior apodemes of Cx-IV, not reduced to a small knob-shaped hump, the presence of eye pigment and P-4 ventral setae approached to slightly developed ventral projection which is located in the distal third of the segment (see Uchida 1935).

Distribution. South Korea (East Sea).