Henlea bidiverticulata Felföldi & Dózsa-Farkas & Nagy & Hong 2020, sp. n.

Henlea bidiverticulata sp. n.

(Figures 2C, 5 – 6)

Type material. Holotype: NIBRIV0000860933, slide No. 2505, adult, stained, whole mounted specimen. Type locality: Mt. Gyebangsan, Nodong-ri, Yongpyeong-myeon, Pyeongchang-gun, Gangwon-do, Korea, soil of Q. mongolica forest, N 37°42’27.92”, E 128°29’02.34”, 848 m asl, 31.10.2017. Paratypes (in total, 19 specimens): NIBRIV0000860934, slide No. 2510, NIBRIV0000860943, slide No. 2511, P.132.1–14, slide No. 2493–2498, 2506, 2508–2509, 2523 (DNA ID: 1201), 2554–2555, 2565, 2567, P.132.15–P.132.17, slide No. 2814–2816, adult, stained whole mounted specimens from the type locality.

Further material examined. Two specimens only in vivo from Mt. Gyebangsan, Nodong-ri, Yongpyeongmyeon, Pyeongchang-gun, Gangwon-do, Korea, soil and litter layers of Q. mongolica forest, N 37°42’24.78”, E 128°29’09.95”, 804 m asl, 31.10.2017.

Etymology. Named after the paired intestinal diverticula.

Diagnosis. The new species can be recognized by the following combination of characters: (1) mobile worms, about 7–10 mm long and 280–410 μm wide at clitellum in vivo, segments 34–46; (2) maximum 6–7–(8) chaetae per bundle; (3) clitellum girdle-shaped: hyaline and granular gland cells in indefinite rows dorsally, but between the bursal slits only granulocytes; (4) five preclitellar pairs of nephridia; (5) two lateral intestinal diverticula in VIII, dorsal vessel origin in IX; (6) coelomocytes oval with fine granules; (7) seminal vesicle absent; (8) sperm funnel small, cylindrical, collar as wide as or slightly narrower than funnel body; (9) spermatheca simple, ampulla slightly wider than the ectal duct, ental ducts unite before joining the oesophagus dorsally.

Description. Very motile worms, mostly covered with soil particles and organic debris. Holotype 4.35 mm long, 270 μm wide at VIII and 270 μm at clitellum, fixed, 44 segments. Body length of paratypes (5.6), 7–10 mm, width 210–370 μm at VIII and 280–410 μm at clitellum in vivo. Length of fixed specimens 3.5–4.9 mm, width 260–380

μm at VIII and 260–420 μm at clitellum. Segments 34–46. Chaetal formula: 3,4,5,(6)–4,5,6: 4,5,6,(7,8)–4,5,6,7(8). Chaetae straight, mostly equal in size within a bundle, 35–46 μm long preclitellarly and 38–50 posteriorly, and 3 μm wide. Chaetae in XII absent. Head pore at 0/I, transverse slit (Fig. 5C). Epidermal gland cells arranged in 4–5 transverse rows per segment (Fig. 5D). Many glands also on the prostomium dorsally (Fig. 5C). Clitellum girdle-shaped in XII–1/2XIII, larger hyaline and smaller granular gland cells in indefinite rows dorsally (Fig. 5E, F); between the bursal slits only granulocytes (Figs 5 G–I). Thickness of body wall about 20–34 μm, cuticle <1 μm in vivo.

Brain incised posteriorly, about 100–150 μm long, in vivo (90–125 μm, fixed) and 1.2–1.9 times longer than wide (Figs 5 A–B). Two pairs (?) of inconspicuous oesophageal appendages in VI, canal in V–IV absent. Mostly all pharyngeal glands free dorsally but close to each other. Sometimes first and third pairs united dorsally, the second pair free (Fig. 6J) or only the third pair united (Fig. 6I), second and third pair with ventral lobes. Chloragocytes from IV about 17–23 μm long (fixed). Dorsal vessel from IX, with heart-like expansions in IX–VII (Figs 2C, 5P), blood colourless, anterior bifurcation in peristomium. Intestinal diverticula a pair of lateral bodies in VIII, rounded or apparently tapering towards free end (Figs 2C, 5 L–M), but laterally visible as flat rounded lobes (Fig. 5N). Inside the diverticula exists a small cavity and some canals (Figs 5L, P). Pars tumida of midgut exhibits a mixture of hyaline and granular epithelium cell-types around the gut wall circumfence, similar to H. glandulifera (type 1, after Rota et al. 1998), in XXII–XXIX, occupying 5–6 segments length (Fig. 6B). Five pairs of preclitellar nephridia, from 6/7 to 10/11, anteseptale small, efferent duct originates anteroventrally (Fig. 5K). Coelomocytes only mucocytes, ellipsoid (Fig. 5J), with fine granula, not brown in transmitted light (length 22–32 μm in vivo, 22–28 μm when fixed). Seminal vesicle absent. Sperm funnel small, cylindrical (Figs 6C, D), about 70–100 μm long and 1.2–2.2 times as long as wide in vivo. Funnel length in fixed specimens 53–76 μm, 1–1.5 times longer than wide. Collar about as wide as funnel body. Spermatozoa about 77–80 μm long, heads 21–26 μm in vivo (30–50 μm and 12–13 μm, fixed), diameter of sperm ducts 6–8 μm in vivo. Penial bulbs (Figs 6E, F) large, compact, about 97–120 μm long, 55–95 μm wide and 50–70 μm high in vivo (65–90 μm long, 55–75 μm wide and 50–70 μm high when fixed). Subneural glands absent. Spermathecae (Figs 2C, 6H, J) simple, without diverticula, ampullae may not be distinctly set off from ectal ducts (diameter of ectal duct about 15–19 μm), ental ducts merging entally and with joint opening into oesophagus in VI dorsally. At the ectal orifice of spermathecal ducts 2–3 variably large glands (20–50 μm long, in vivo) (Figs 6 G–H). 1–3 mature eggs at a time.

Distribution and habitat. In Korea: Mt. Gyebangsan, Nodong-ri, Yongpyeong-myeon, Pyeongchang-gun, Gangwon-do, Q. mongolica forest, N 37°42’27.92”, E 128°29’02.34”, 848 m asl; Mt. Gyebangsan, Nodong-ri, Yongpyeong-myeon, Pyeongchang-gun, Gangwon-do, soil and litter layers, N 37°42’24.78”, E 128°29’09.95”, 804 m asl.

Differential diagnosis. Henlea bidiverticulata sp. n. and six other Henlea species are characterized by one pair of free-projecting lateral intestinal diverticula in VIII. Among them, three species found in North America (H. glabra Altman, 1936, H. urbanensis Welch, 1914, H. eiseni Bell, 1942) are much larger (66–71, 65–66 and 50–53 segments, respectively, vs. 34–46 segments in the new species). H. nasuta (Eisen, 1878) is also much larger (15–25 mm long in vivo, vs. 5.5–10 mm in H. bidiverticulata), moreover it has larger intestinal diverticula, the origin of the dorsal vessel lies between the diverticula in VIII (Fig. 8A), and the coelomocytes are rounded, dark brown (Figs 8B, C). The ampulla of spermatheca is conspicuous in H. nasuta, but narrower in H. bidiverticulata sp. n. (Fig. 8C, vs. Fig. 6H). In H. similis Nielsen & Christensen, 1959, the ampulla of the spermatheca is more similar to the new species (Fig. 8D) but the intestinal diverticula occupy also posteriorly parts of IX (Fig. 8E), whereas in the new species this organ originates at 8/9 and is confined to VIII (Figs 5 L–P). In many traits H. bidiverticulata sp. n. is most similar to H. glandulifera Nurminen, 1970, e.g., size and the number of segments [8–12 mm, 36–50 segments in vivo in H. glandulifera (vs. 7–10 mm, 34–46 segments)], the arrangement of the clitellar glands (Figs 7A, B vs. Figs 5 E–I), epidermal glands (Fig. 7C vs. Fig. 5D), the form and size of intestinal diverticula (Fig. 7 D–F vs. Figs 5 L–P, 6A)], but differs from it and from the other two species mentioned above by the origin of dorsal vessel in IX (Figs 5M, P.

Moreover, the new species has only 5 pairs of preclitellar nephridia [vs. six pairs in H. glandulifera (Rota et al. 1998)]. The sperm funnel is also smaller: 70–100 μm long in vivo (53–76 μm, fixed), but in H. glandulifera 95–140 μm in vivo (<90 μm, fixed), based on the obervations of K. Dózsa-Farkas [unpublished; Fig. 7G vs. Figs 6C, D; according to Rota et al. (1998) <140 μm in vivo and 136–177 μm when fixed]. Spermatozoa are also smaller: length 72–80 μm, heads 21–26 μm in the new species, while 95–150 μm and 35–60 μm in H. glandulifera after own observations, and 105 μm and 27 μm after Rota et al. (1998) in vivo. Besides, in H. glandulifera there are two conspicuous winding channels above the oesophagus in V from the oesophageal appendages (Fig. 7J), which are absent in the new species. The molecular taxonomic results also support the description of the new Henlea species (see below).