Cognettia koreana Felföldi & Dózsa-Farkas & Nagy & Hong 2020, sp. n.

Cognettia koreana sp. n.

(Figures 2A,B, 3, 4)

Type material. Holotype: NIBRIV0000860931, slide No. 2422, adult, stained, whole mounted specimen. Type locality: Mt. Deogyu, Seolcheon-myon, Muju-gun, Jeollabuk-do, Korea, soil and litter layers, Abies holophylla forest, N 35°51’34.1”, E 127°44’49.1”, 1492 m asl, 21.09.2016. Paratypes (in total, 13 specimens): NIBRIV0000860932, slide No. 2421 from type locality, NIBRIV0000860942, slide No. 2786 from locality: Mt. Gyebangsan, Nodong-ri, Yongpyeong-myeon, Pyeongchang-gun, Gangwon-do, Korea, soil and litter layers, Quercus mongolica forest, N 37°42’24.78”, E 128°29’09.95”, 804 m asl, 31.10.2017. P.131.1, slide No. 2294, P.131.2, slide No. 2304, P.131.3– P.131.6, slide No. 2407–2410, P.131.7–131.8, slide No. 2417–2418, P.131.9–131.11, slide No. 2420, 2423–2424 all from type locality.

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Further material examined. Five specimens from the type locality and one specimen from Mt. Gyebangsan, only in vivo.

Etymology. Named after the country where it was found.

Diagnosis. (1) Small size (3–6 mm, in vivo), segments 23–26; (2) chaetae maximum 3–4 per bundle, slightly sigmoid without nodulus; (3) four pairs of nephridia preclitellarly; (4) all dorsal lobes of the three pairs of pharyngeal glands free and with ventral lobes, and 2 pairs of secondary ventral lobes in V, VI; (5) dorsal blood vessel from XII, blood colourless; (6) sperm funnel small (35–50 μm long); (7) spermatheca entally free, made of a thick-walled, 35–50 μm long and 12–17 μm wide ectal duct with a sessile ectal gland and a thin-walled ampulla; (8) some mature eggs at a time.

Description. Small worm. Holotype 2.6 mm long, 225 µm wide at VIII and 255 µm at clitellum (fixed), 26 segments. Length of paratypes 3.2–6.0 mm, width 150–230 µm at VIII and 180–340 µm at clitellum in vivo, length of fixed specimens 2.3–2.6 mm, width 150–270 µm at VIII and 220–270 µm at clitellum, segments 23–26. Chaetae sigmoid, without nodulus. Chaetal formula 2,3–2,(3): 2,3,(4)–(2),3,4, length 30–37 µm in preclitellar region, 39–50 µm in posterior segments, 2.5–3 µm wide, absent in XII. Epidermal glands inconspicuous. Body wall 16–20 μm thick, cuticle 1 μm, or <1 μm, fixed. Clitellum extending over XII–1/2XIII, saddle-shaped, absent midventrally with about 90 µm wide gap (Figs 3C, 4 D-E). Around the male glandular bulbus and at the ventral margin only granular cells. Clitellar gland cells irregularly scattered dorsally (Figs 3B, D). Head pore 0/I.

Brain about 100 μm long and 1.3–1.5 times longer than wide (fixed and in vivo alike), anteriorly slightly convex, posteriorly deeply incised (Fig. 3A). Three pairs of primary pharyngeal glands, all free dorsally, first pair the largest, all with ventral lobes and two pairs of secondary glands in V and VI (Fig. 3E, F, I). Chloragocytes large, 20–30 μm long in vivo (Fig. 3H). Dorsal blood vessel from XII, blood colourless. The anterior bifurcation in peristomium. Four pairs of nephridia preclitellarly from 6/7 to 9/10; anteseptale consisting of funnel only, efferent duct arises antero-ventrally (Fig. 3G) (one specimen has only three pairs of nephridia preclitellarly). Coelomocytes transparent, elongated oval, about 21–27 μm long in vivo (15–23 μm, fixed) (Fig. 3H). Pars tumida of midgut at XVIII–XX (occupying 2 segments). Seminal vesicle absent. Sperm funnels (Figs 2A, 4 A–C) small, 35–50 μm long and 1.2–1.5 times longer than wide in vivo (28–50 μm long and 1.5–2 times longer than wide in fixed specimens); sometimes stubby and slightly longer than wide (Fig. 4B); the collar as wide as funnel body or slightly narrower. Diameter of sperm ducts about 7 μm. Spermatozoa 41–48 μm long, head 20–30 μm in vivo (25–45 μm long, head 13–15 μm, fixed). Male glandular bulb (Fig. 4D, E) compact, oval, about 50 μm long, 30 μm wide in vivo (30–45 μm long and 25–45 μm wide when fixed). Spermathecae (Figs 2B, 4 G–J) confined to V, entally free. Ectal ducts thick-walled, 35–50 μm long and 12–17 μm wide in vivo [30–44 μm long (in one case 60 μm) and 8–10 μm wide, fixed] with one sessile gland (15–22 μm long, fixed) at the orifice (Fig. 4I). The ampulla thin-walled, 33–50 μm long, 17–22 μm wide in vivo (25–35 μm long, 18–25 μm wide, fixed), with sperm in the lumen. 1–4 large mature eggs at a time (Fig. 4F).

Distribution and habitat. In Korea: Mt. Deogyu, Seolcheon-myon, Muju-gun, Jeollabuk-do, soil and litter layers of Abies holophylla forest, N 35°51’34.1”, E 127°44’49.1”, 1492 m asl; Mt. Gyebangsan, Nodong-ri, Yongpyeong-myeon, Pyeongchang-gun, Gangwon-do, soil and litter layers of Q. mongolica forest, N 37°42’24.78”, E 128°29’09.95”, 804 m asl.

Differential diagnosis. Seven species are similar to the new species in size and in that they reproduce only sexually: C. zicsii Dózsa-Farkas, 1989, C. lapponica Nurminen, 1965, C. bisetosa Christensen & Dózsa-Farkas, 1999, C. quadrosetosa Christensen & Dózsa-Farkas, 1999, C. floridae Healy, 1996, C. hibernica Healy, 1975 and C. baekrokdamensis (Dózsa-Farkas et al. 2018). C. pseudosphagnetorum was also assumed to reproduce only sexually by Martinsson et al. (2015a), but we disagree with this opinion. The main differences that distinguish these from the new species are the followings: C. baekrokdamensis and C. floridae have asymmetrical ectal swellings of the spermathecal ducts (which is absent in the new species). In C. bisetosa and C. hibernica, the maximum number of chaetae per bundle is two. C. quadrosetosa has 3–4 chaetae per bundle laterally, while in the new species lateral bundles have only 2–3 chaetae. In the new species, bundles of four chaetae occur only ventrally. C. lapponica and C. zicsii are slightly larger than the new species: 32–37 segments, 6–8 mm body length in C. lapponica, and 34–47 segments, 7–10 mm in C. zicsii in vivo; the sperm funnel is also larger (120–180 μm long in vivo in C. lapponica and 140–240 μm long in C. zicsii).