Bryodrilus hallasanensis Dózsa-Farkas & Felföldi & Nagy & Hong 2018, sp. n.

Bryodrilus hallasanensis sp. n.

(Figures 5F, 6, 7)

Type material. Holotype: NIBRIV0000810590, slide No. 2199, adult, stained whole mounted specimen. Type locality: Mt. Hallasan in Gwaneumsa trail, Jeju Island, Korea, soil and litter layers of Sorbus commixta tree, N 33˚22'06.8", E 126˚32'02.2", 1694 m asl, 0 9.06.2016, leg. Y. Hong. Paratypes (in total 18 stained, adult specimens on slides and 47 specimens in 70% ethanol): NIBRIV0000810591, slide No. 2177, from type locality, NIBRIV0000811382, slide No. 2377, site 4, P.115.1.1-115.1.6, slides No. 2174-2175, 2178, 2200-2202, from type locality, P.115.2.1-115.2.8 slides No. 2181-2183, 2258, 2373-2376, site 4, P.115.3, slide No. 2327, site 2, P.115.4, slide No. 2328, site 8. In 70% ethanol: P115.5, from type locality, three species P.115.6, site 2 one specimen; P.115.7, site 4 35 specimens; P.115.8, site 6 one specimen; P.115.9, site 11 six specimens; P.115.10, site 12 one specimen.

Further material examined. 16 specimens investigated in vivo, 4 of them processed for DNA analysis.

Etymology. Named after the mountain where it was found.

Diagnosis. The new species can be recognized by the following combination of characters: (1) small size (5–8 mm in vivo), segments 30–40; (2) chaetae maximum 4–5 per bundle, slightly sigmoid without nodulus; (3) conspicuous epidermal gland in 5–6 rows; (4) four pairs of preclitellar nephridia; (5) coelomocytes oval or discoid with fine granules; (6) pharyngeal glands free dorsally and with ventral lobes; (7) two pairs of irregularly lobed oesophageal appendages in VI, with small canals; (8) sperm funnels pear-shaped, 70–120 µm long and 2–3 times longer than wide; (9) seminal vesicle small; (10) male copulatory organs spherical, diameter about 60–80 µm; (11) spermathecae communicating with oesophagus, ectal ducts 60–90 µm long and 13–18 µm wide, the ampullae lemon-shaped, diameter 20–30 µm, ectal gland absent.

Description. Small lively worm. Holotype 5.2 mm long, 240 µm wide at VIII and 250 µm at clitellum (fixed), 35 segments. Length of paratypes 5–8 mm, width 200–260 µm at VIII and 2 40–330 µm at clitellum in vivo, length of fixed specimens 2.9–5.2 mm, width 170–220 µm at VIII and 210–250 µm at clitellum, segments (24) 30–40. Chaetae slightly sigmoid, without nodulus. Chaetae in a bundle arranged in asymmetric fan of unequal size, those towards dorsal and ventral midlines of body gradually smaller; largest ventral chaetae in a bundle preclitellarly 33– 37 µm, the next in line 34–30 µm, 29–25, and 28–23 µm long and 1.8–2 µm wide. In terminal segments the largest chaetae slightly longer, 40–45 µm. Chaetal formula 2,3,4 – 3: 3,4,(5) – 4,3 (2). Chaetae absent at XII. In ventral preclitellar bundles usually 4 chaetae, 5 in some bundles in some specimens from site 4. Epidermal gland cells conspicuous preclitellarly, 5–6 rows per segments (Fig. 6A). Head pore at 0/I, a longitudinal slit. Body wall 20–30 µm thick, cuticle thin about 1 µm, longitudinal muscle layer well-developed. Clitellum from XII–1 /2 XIII, hyalocytes and granulocytes in rows dorsally, hyalocytes larger than granulocytes, the latter often triangle-shaped (Fig. 6B), absent ventrally (about 70 µm distance) (Fig. 7G).

Brain 95–110 µm long and 1.7–2.2 times longer than wide (fixed and in vivo), anteriorly slightly convex, posteriorly rounded (Fig. 6C–D). Pharyngeal glands 3 pairs in IV–VI, mostly all free dorsally with ventral lobes (Fig. 6H), sometimes first pair connected dorsally. Oesophageal appendages (Figs. 6H, 7A–B) in VI, two pairs of irregularly lobed bodies (about 30–50 µm long) attached to oesophagus ventro-laterally with small canals (these canals collapse under longer examination in vivo and give a homogeneous aspect of the structure). Intestine widening abruptly in VII and VIII (Fig. 6E). Four pairs of preclitellar nephridia from 6/7 to 9/10; anteseptale consisting of funnel only, medial rise of efferent duct (Figs. 6F,G). Coelomocytes nucleate, oval or discoid, about 15–26 µm long in vivo (13–17 µm, fixed), finely granulated (Fig. 7C,D). Dorsal blood vessel from XIII, blood colourless. Anterior bifurcation in peristomium (Fig. 6C). Pars tumida of midgut XX–XXVI, occupying 2–3 segments. Chloragocytes from VI, about 12–18 µm large. Seminal vesicle small in XI. Sperm funnels (Fig. 7E,F) pear-shaped, 70–120 µm long and 2–3 times longer than wide in vivo (60–95 µm long and 1.5–2 times longer than wide in fixed specimens). The collars well developed, as wide as funnel body or narrower. Diameter of sperm ducts 6–8 µm. Spermatozoa 70–85 µm long, heads 22–30 µm in vivo. Male glandular bulb spherical, diameter about 60– 80 µm in vivo (40–70 µm, fixed) (Fig. 7G,I). Bursal slits longitudinal, bent laterally. Subneural glands absent. Spermathecal ectal ducts about 60–90 µm long and 13–18 µm wide in vivo (50–80 µm long and 12–14 µm wide, fixed), no ectal glands, the ampullae lemon-shaped, diameter 20–30 µm in vivo and 22–25 µm, fixed. The ental ducts merging entally and with joint opening into oesophagus in VI (Figs. 5F, 7J). 1–3 mature egg at a time.

Distribution and habitat. In Korea, Mt. Hallasan, sites 2, 4–6, 8, 11, 12. Dominant at sites 4, 5.

Differential diagnosis. Among the previously described Bryodrilus species, four species have fewer than 40 segments and 7 mm length in vivo: B. librus (Nielsen & Christensen, 1959), B. diverticulatus Černosvitov, 1929, B. tunicatus Dózsa-Farkas & Christensen, 2002, B. archipelagicus Christensen & Dózsa-Farkas, 2006, but clearly separate from this species in the following main characters: B. librus has 5 pairs of preclitellar nephridia, the oesophageal appendages are rounded, well visible and the midgut pars tumida can be found more forward (in XVII–XX), while the new species has only 4 pairs of preclitellar nephridia, the oesophageal appendages are lobed, not easily seen and the midgut pars tumida occupies 2–3 segments (in segments XX–XXVI). B. diverticulatus differs by 5 pairs preclitellar nephridia and hollow and pulsating oesophageal appendages. B. tunicatus has larger sperm funnels (200–300 µm long 4–5 times longer than wide vs. 70–120 µm and 2–3 times longer than wide, in the new species) and spermathecae with sessile diverticula in which the spermatozoa are arranged in smaller bundles. The spermathecae of B. archipelagicus are more conspicuous: the ectal duct is 220 µm long and approximately 30 µm wide and the diameter of ampullae is 90–95 µm (the ducts has a size of 60–90 to 13–18 µm and the ampullae 20–30 µm in B. hallasanensis sp. n.).