Mesenchytraeus calyx Dózsa-Farkas, Felföldi & Hong, 2015, sp. n.

Mesenchytraeus calyx sp. n.

(Figures 6 H–K, 9, 10, 11)

Type material. Holotype. NIBRIV0000320525, slide No. 1173 a+b, adult, stained and whole-mounted specimen, anterior part of the worm opened dorsally, fixed 23.02.2015. Type locality: site 8: Mt. Cheontae, Yeongdong-gun, Cheungcheongnam-do, Korea, 36º09'29.8"N 127º36'49.8"E, 248 m asl, soil and litter layers of broad-leaved forest, leg. Y. Hong, 15.05.2014.

Paratypes. NIBRIV0000320526, slide No. 2005, adult, stained whole mounted, anterior part of the worm opened. NIBRIV0000320527, one adult specimen in 70 % ethanol, both from site 11: Sulchon-myeon, Muju-gun, Jeollabuk-do, Korea, 35º59'28.7"N 127º50'46.8"E, 544 m asl, soil and litter layers of forest, leg. Y. Hong, 16.05.2014. Fixed 15.04.2015. P.107.1–107.2, slides No. 1156a+b; 2002a+b two adult, stained, whole mounted specimens, site 11: Sulchon-myeon, Muju-gun, Jeollabuk-do, Korea, 35º59'28.7"N 127º50'46.8"E, 544 m asl, soil and litter layers of forest, leg. Y. Hong, 16.05.2014. Fixed 18.02.2015 and 26.03.2015. P.107.3–107.8, slides No. 1149a+b, 1155a+b, 1157a+b, 1162a+b, 1163a+b, 2003a+b, six adult, stained specimens, anterior part of the worms opened dorsally, fixed 17.02– 26.03.2015, from site 1: College of Agriculture & Life Science, Chonbuk National University, Jeonju-si, Jeollabuk-do, Korea, 35º50'59.0"N 127º07'56.4"E, 55 m asl, soil and litter layers of woodland, leg. Y. Hong, 19.05.2014. P.107.9–107.10, slide No. 1181, 2004a+b, two adult, stained specimens, anterior part of the worm opened dorsally, fixed 15.04.2015, from type locality. P.107.11, slide No. 2006, one juvenile specimen, fixed 26.03.2015, from type locality.

Further material examined. 1 specimen in 70 % ethanol from site 8 and 5 juveniles from sites 1, 11 and 8.

Etymology. Named after the cup-shaped spermathecal ampulla (calyx = cup, Latin).

Diagnosis. The new species can be recognized by the following combination of characters: (1) large wide worms (27–42 mm long and about 0.9–1 mm wide, in vivo), segments 60–84; head and the body dorsally brown pigmented; (2) chaetae sigmoid, with nodulus, maximum 6–7 per bundle, in VII–X ventrally only 2–3 enlarged chaetae; (3) clitellum girdle-shaped: gland cells small, in reticulate pattern; (4) five preclitellar pairs of nephridia; (5) dorsal blood vessel from XXIII–XXV, blood light pink; (6) two pairs primary and 3 pairs secondary pharyngeal glands, not connected dorsally; (7) small lemon-shaped coelomocytes, light yellow in aggregations in vivo; (8) sperm sacks and egg sack may extend into XXX and XLI; (9), atrium long with 5–6 very large atrial glands, numerous accessory copulatory glands of different size extending around male pores; (10) spermathecae with long ectal ducts, projecting deeply into the cup-shaped ampullae, which have 7–9 diverticula; ental ducts connected with oesophagus in V–VII.

Description. Large enchytraeid worm. Colour light pink, dorsal side is light-brown preclitellarly, while the prostomium is dark brown by pigmentation (Fig. 9 A–C). Holotype 20.7 mm long, 900 µm wide at VIII and 960 µm at the clitellum, fixed, 83 segments. Body length of paratypes 27–42 mm, width 850–1000 µm at VIII and 1005– 1050 µm at clitellum, in vivo. Length of fixed specimens 20–39 mm, width 900–1050 µm at VIII and 960–1250 µm at clitellum. Segments 60–84. Strong external segmentation at body end (Fig. 10 C). Chaetae sigmoid with nodulus. Chaetal formula: 2,3,4 – 3,2,4,5,(6): 4,5,6,2,3 – 4,5,6,(7,3,2). Chaetae mostly unequal in size within the bundle: in ventral bundles a gradual increase in length towards the ventral midline and in lateral bundles increase to the dorsal direction. The length of the longest chaetae gradually increasing from II to VI (from 100 or 125 x 8–10 µm to 150–170 x 9–10 µm). From VII to XI only 3 or 2 chaetae in ventral bundles (rarely 4 in XI), they are larger and stronger (200–240 x 15–18 µm). Chaetae of lateral bundles smaller and thinner than ventrals (about 103–150 x 10–12 µm). Postclitellarly longest chaetae measuring 150–190 x 9–10 µm. Chaetae in XII absent. Head pore at 0/I, a large transverse slit (Figs. 9 C, 10A). Clitellum girdle-shaped in 1/ 2XI –XIV, extending over 2.5–3 segments (up to four segments, slide No. 1149), gland cells small in reticulate pattern, also between bursal slits (Figs. 10 B, 11B). In one case gonadal region shifted forwards by 4 segments: clitellum in 1/ 2VII –1/ 2X, bursal slits in VIII (paratype P.107.7 slide No. 1163a). Thickness of body wall about 80–150 µm, depending on state of sexual maturity, cuticle about 1–2 µm, fixed.

Brain incised anteriorly and slightly convex posteriorly, slightly longer than wide (about 150 x 180 µm, fixed) (Figs. 6 H, 10A). Two pairs of primary pharyngeal glands (in 4/5–5/6), not united dorsally, and two or three (four in the holotype) pairs of secondary pharyngeal glands in V–VI or V–VII (VIII); the secondary glands lobed (Fig. 10 E). Yellow-brownish chloragocytes (Fig. 9 A,D) from IV, about 20–25 µm long, fixed. Dorsal blood vessel from XXIII–XXV, anterior bifurcation in I, blood pale reddish. Five pairs of preclitellar nephridia (Fig. 10 D) from 6/7 to 10/11, anteseptale funnel only, postseptale lobed with folded canal, no interstitial tissue, efferent duct arising between the lobes. Oesophageal and intestinal appendages or diverticula absent. Coelomocytes only mucocytes, lemon-shaped, with granula, in cell aggregations light yellowish in vivo, small, size of cells 16–21 µm.

Sperm sac (Fig. 9 A,B) extending backwards to XXII–XXX, egg sack to XXV–XLI. In sperm sack many sperm bundles (Fig. 10 F), about 88–110 µm long, with spermatozoal heads at one end, 26–30 µm long and 23–28 µm wide (Fig. 6 I). Sperm funnel thick-walled, about 500–600 µm long and 2 times as long as wide, fixed, the collar widely opened and bending outwards (Fig. 11 C), often longer on side. Sperm duct very long, reaching as far as XV–XVII, loosely coiled, diameter 35–40 µm, fixed; diamaeter gradually increasing towards atrium. Maximum width of atrium 90–120 µm, here joined by 5–6 very large atrial glands (prostate glands), usually 250–350 µm long, up to 600–700 µm (Figs. 6 K, 10H, 11A). The atrium connects through a duct (120–210 µm long and 40–45 µm wide, fixed) with the male copulatory organ, which is surrounded by many accessory copulatory glands of different size (Figs. 6 K, 10G, 11A). The everted bursa may be remarkable (Fig. 11 A). Bursal slits large, irregular, transversal, in XII (Fig. 11 B). Subneural glands absent. Spermathecae (Figs. 6 J, 9D, 11D,E): ectal ducts long (400– 820 µm long and 40–65 µm wide), devoid of glands. Spermathecal pores in 4/ 5 in lateral position as wavy transverse gaps (Fig. 11 F). Ampullae mostly in VI but sometimes in V or VII. Lengths of ectal ducts often unequal, e.g. when one ampulla lies in V and the other one in VI or VII. Ducts projecting deeply into the cup-shaped ampullae (their length inside ampulla 150–200 µm, width at the end about 50 µm) (Figs. 6 J, 11E). Ampullae 250– 350 µm long, 200–260 µm wide. Ectal end of ampullae with an ectally oriented collar of about 7–9 pointed diverticula of various length (100–200 µm) (Figs. 6 J, 11D,E). In one case (slide No. 1155) we can see these diverticula from above and count the number of diverticula (Fig 9 E). Spermatozoa appear to be hanging out from the wall of diverticula (Fig. 9 F). Ampullae continuing entally into a flexible elongate bag which ends in VI or VII, here apparently connected to the oesophagus. Eggsack with submature eggs only.

Distribution and habitat. In Korea site 1: College of Agriculture & Life Science, Chonbuk National University, Jeonju-si, Jeollabuk-do, 35º50'59.0"N 127º07'56.4"E, 55 m asl, woodland; site 8: Mt. Cheontae, Yeongdong-gun, Cheungcheongnam-do 36º09'29.8"N 127º36'49.8"E, 248 m asl, forest; site 11: Sulchon-myeon, Muju-gun, Jeollabuk-do, 35º59'28.7"N 127º50'46.8"E, 544 m asl, mixed forest.

Differential diagnosis. Up to now, seven valid species of Mesenchytraeus have been reported with enlarged ventral chaetae: M. tetrapodus Timm & Popchenko, 1978, M. crenobius Timm, 1994, M. kontrimavichusi Piper et al., 1982, M. gigachaetus Xie, 2012 (a replacement name for M. megachaetus Shen et al., 2011), M. longiductus Christensen & Dózsa-Farkas, 2012, M. anisodiverticulatus Shen et al., 2012, and M. monodiverticulatus Shen et al., 2012. The main differences between these species and the new species are as follows: M. kontrimavichusi is smaller (12 mm long, 53 segments), spermathecae have one diverticulum each, and there is no atrium; M. crenobius has two spermathecal diverticula and the dorsal blood vessel origin in the clitellar region. M. tetrapodus has only one enlarged chaeta per ventral bundle, six pairs of preclitellar nephridia and the spermathecae attached to the oesophagus in IX–X; M. gigachaetus is smaller (10–13 mm long, 31–50 segments) and without atrial glands; the spermathecae of M. anisodiverticulatus have two asymmetrical diverticula with short ental ducts attached to the oesophagus in V, and atrial glands are absent; M. monodiverticulatus is smaller (6–10 mm, 39–58 segments), has more (4–5) enlarged chaetae in V–VI, one spermathecal diverticulum, and no atrial glands. M. longiductus is smaller (7.5–15 mm long, 48-55 segments), spermathecae are onion-shaped devoid of diverticula, and there are only two large atrial glands (Timm 1994; Timm & Popchenko 1978; Piper et al. 1982; Christensen & Dózsa-Farkas 2012; Shen et al. 2011, 2012a, b; Xie 2012). The spermathecae of M. mirabilis Eisen, 1878 are slightly similar to the spermathecae of the new species, but the ectal ducts are very short and the diverticula are roundish, moreover enlarged chaetae are absent (Eisen 1879; Christensen & Dózsa-Farkas 1999).