Mesenchytraeus longidiverticulatus, Felföldi & Dózsa-Farkas & Nagy & Hong, 2020

Felföldi, Tamás, Dózsa-Farkas, Klára, Nagy, Hajnalka & Hong, Yong, 2020, Three new enchytraeid species (Enchytraeidae, Annelida) from mountain soils of Korea and ten species new for the country, Zootaxa 4896 (1), pp. 1-45 : 20-24

Mesenchytraeus longidiverticulatus sp. n.

( Figures 2D – F , 9 , 10 )

Type material. Holotype: NIBRIV0000860935, slide No. 2593, adult, stained specimen. Type locality: Mt. Gyebangsan , Nodong-ri , Yongpyeong-myeon , Pyeongchang-gun, Gangwon-do, Korea, Q. mongolica forest, N 37°42’27.92”, E 128°29’02.34”, 848 m asl, 31.10.2017 . Paratypes (in total, 11 stained, adult specimens on slides): NIBRIV0000860936, slide No. 2608, one adult, stained specimen, locality: Mt. Chiaksan , Hakgok-ri , Socho-myeon , Wonju-si, Gangwon-do, Korea, soil and litter layers of mixed forests, N 37°22’58.07”, E 128°03’30.83”, 484 m asl, 02.11.2017 . NIBRIV0000860944, slide No. 2791, Mt. Gyebangsan , Nodong-ri , Yongpyeong-myeon , 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 . P.133.1–P.133.4, slide No. 2594–2596, 2620, from type locality. P.134.1–P.134.2, slide No. 2591, 2614, locality: Mt. Chiaksan , Hakgok-ri , Socho-myeon , Wonju-si, Gangwon-do, Korea, soil and litter layers of mixed forests, N 37°22’58.07”, E 128°03’30.83”, 484 m asl, 02.11.2017 . P. 134.3, slide No. 2613, locality: Mt. Chiaksan , Hakgok-ri , Socho-myeon , Wonju-si, Gangwon-do, Korea, soil of mixed forests and Quercus serrata forest, N 37°23’36.50”, E 128°03’15.30”, 395 m asl, 02.11.2017 . P. 135, slide No. 2530, locality: Mt. Odaesan , Sangwonsa , Dongsan-ri , Jinbu-myeon , Pyeongchang-gun, Gangwon-do, Korea, soil and litter layers of mixed forest, N 37°47’03.63”, E 128°33’44.06”, 906 m asl, 01.11.2017 . P. 136, slide No. 2894 (last 14 segments, 1.4 mm, for DNA analysis: ID 1416), locality: Mt. Gongjaksan , Gurun-ri , Hwachon-myeon , Hongcheon-gun, Gangwon-do, Korea, soil and litter layers of Q. mongolica and mixed forests, N 37°42’15.71”, E 128°00’43.41”, 403 m asl, 25.10.2019 .

Further material examined. Five subadults from type localiy, from Mt. Chiaksan and Mt. Gwaebangsan , Gangdong-myeon , Gangneung-si , Gangwon-do , Korea, soil and litter layers of Q. mongolica forests, near to Deungmyeongnakgasa temple of Mt. Gwaebangsan, N 37°42’31.76”, E 129°00’17.54”, 144 m asl, 10.11.2018 .

Etymology. The species is named after the shape of the spermathecal diverticula.

Diagnosis. The new species can be recognized by the following combination of characters: (1) middle sized worms (6–13 mm long and about 330–510 µm at clitellum in vivo), segments 40–55, colour whitish; (2) chaetae sigmoid with nodulus, maximum 4–5 per bundle, in V–VII ventrally only 2–3 slightly enlarged chaetae, but the size from VII–XI ventrally about the same or slightly smaller; (3) clitellum girdle-shaped: gland cells in reticulate pattern; (4) five preclitellar pairs of nephridia; (5) dorsal blood vessel from XV–XIX, blood colourless; (6) two pairs of primary and 3–4 pairs of secondary pharyngeal glands, not connected dorsally; (7) small lemon-shaped coelomocytes, light yellow in aggregations in vivo; (8) sperm funnels thick-walled, about 400–580 µm long and 3–7 times longer than wide in vivo, sperm ducts long, reaching as far as XV–XVI; (9) sperm sacs may extend into XV–XVIII, egg sac to XVI–XX; numerous penial glands and some slightly larger accessory copulatory glands extending around male pores; (10) spermatheca attached to the oesophagus in VI–VII, ectal ducts of varying length (150–300 µm long and 30–53 µm wide in vivo), globular ampulla with a very long diverticulum (up to 500 µm long and 30–45 µm wide).

Description. Middle-sized enchytraeid worm. Colour whitish. Holotype 7.8 mm long, 360 µm wide at VIII and 390 µm at clitellum (fixed), segment number 49. Body length of paratypes 6–13 mm, width 300–480 µm at VIII and 330–510 µm at clitellum in vivo; length of fixed specimens 3.9–7 mm, width 260–390 µm at VIII and 260–450 µm at clitellum. Segments 40–55. Chaetae sigmoid with nodulus. Chaetal formula: 2,3–2,3: 3,4,3,2,5,(6)–3,4,(5),3,2. Chaetae mostly unequal in size within a bundle: in ventral bundles a gradual increase in length towards the ventral midline and in lateral bundles an increase in length in dorsal direction, as usual in most Mesenchytraeus species ( Dózsa-Farkas et al. 2018). In II–IV mostly 3–4 (5) chaetae per bundle ventrally, in V–VI 2–3, in VII–VIII 2–4 (5) chaetae, in IX–XI 3–4, rarely 2 or 5 chaetae. The size of the longest chaetae ventrally gradually increasing from

II to VII from 45–50 × 3.5–4 µm to 60–80 µm (maximum 100 µm) × 5–7 µm, the larger and stronger chaetae occur in V and VI. From VII to XI slightly smaller again (50–75 µm by 5 µm) ( Fig. 9F ). Chaetae of lateral bundles slightly smaller and thinner than ventrals and gradually increasing from II to XI (from 36–47 µm to 50–55 µm by 3–4 µm). At the posterior body end, longest chaetae measuring 60–65 by 5–6 µm. Chaetae in XII absent. Head pore on prostomium, a large transverse slit ( Fig. 9E ). Clitellum girdle-shaped in XI–XIII or XI–1/2XIV, gland cells in reticulate pattern ( Figs 9B, C ), between bursal slits less developed ( Fig. 9D ). Thickness of body wall about 30–45 µm, depending on state of sexual maturity, cuticle about 1 µm. Epidermal gland cells sometimes densely aggregated in segments I-III dorsally ( Fig. 9G ).

Brain ( Fig. 9A ) incised anteriorly and slightly concave posteriorly, slightly wider than long (80–105 µm long, in vivo). Two pairs of primary pharyngeal glands (in 4/5, 5/6), not united dorsally, and three or four pairs of secondary pharyngeal glands in V–VII (VIII); the secondary glands lobed. Yellow-brownish chloragocytes from IV, about 21–26 µm long in vivo. Dorsal blood vessel from XV–XIX, anterior bifurcation in I ( Fig. 9A ), blood colourless. Five pairs of preclitellar nephridia 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 22–30 µm ( Fig. 9H ). Sperm sac extending backwards to XV–XVIII, egg sac to XVI–XX. In sperm sac sperm bundles in rolls ( Fig. 10E ). Sperm funnel ( Figs 9 I–L) thick-walled, about 400–580 µm long and 3–7 times longer than wide in vivo (200–300 µm long, and 3–3.5 times longer than wide, when fixed), mostly reclinate. Sperm duct long, reaching as far as XV–XVI, loosely coiled, diameter 15–21 µm (in vivo); diameter gradually increasing towards atrium. Atrium ( Figs 2F , 10 A–D) 250–400 µm long, maximum width 50–65 µm ( Fig. 10D ), here joined by 4 very large atrial glands (prostate glands), usually 120 – 280 µm long ( Figs 10B, D ). The atrium connects through an ectal duct (50–120 µm long, in vivo) to the penial bulb, which is surrounded by small penial glands and some accessory glands (about 50 – 100 µm long) ( Fig. 10C ). Bursal slits large, irregularly transversal, in XII. Subneural glands absent. Spermathecae connected with the oesophagus ( Figs 2D , 10 F–J): ectal ducts with variable length, 150–300 µm long and 30–53 µm wide in vivo (60 – 128 µm long and 32–50 µm wide, fixed), devoid of glands. Spermathecal pores in 4/ 5 in lateral position, canal 4–6 µm wide at opening with strong cuticular lining ( Fig. 10K ). Ampulla globular, diameter about 70–110 µm, with one long diverticulum, whose length reaches 500 µm and width 30–45 µm when filled with sperm, in vivo (130–190 µm long, when fixed). The diverticula can extend posteriorly into VI and/or VII. Sometimes they take a forward direction. Ampulla continuing entally into a flexible elongate ental duct, which ends in VI connected to the oesophagus ( Figs 10 F–J).

Distribution and habitat. In Korea: Mt. Gyebangsan, Nodong-ri, Yongpyeong-myeon, Pyeongchang-gun, Gangwon-do, Korea, Q. mongolica forest, N 37°42’27.92”, E 128°29’02.34”, 848 m asl; Mt. Gyebangsan, Nodongri, Yongpyeong-myeon, Pyeongchang-gun, Gangwon-do, soil and litter layers, N 37°42’24.78”, E 128°29’09.95”, 804 m asl; Mt. Chiaksan, Hakgok-ri, Socho-myeon, Wonju-si, Gangwon-do, soil of mixed forests and Q. serrata forest, N 37°23’36.50”, E 128°03’15.30”, 395 m asl; Mt. Chiaksan, Hakgok-ri, Socho-myeon, Wonju-si, Gangwondo, soil and litter layers of mixed forests, N 37°22’58.07”, E 128°03’30.83”, 484 m asl; Mt. Gwaebangsan, near to Deungmyeongnakgasa temple of Mt. Gwaebangsan, Gangdong-myeon, Gangneung-si, Gangwon-do, soil and litter layers of Q. mongolica forests, N 37°42’31.76”, E 129°00’17.54”, 144 m asl; Mt. Gongjaksan, Gurun-ri, Hwachonmyeon, Hongcheon-gun, Gangwon-do, soil and litter layers of Q. mongolica and mixed forests, N 37°42’15.71”, E 128°00’43.41”, 403 m asl.

Differential diagnosis. Up to now, twelve valid species of Mesenchytraeus have been reported with one spermathecal diverticulum. Among these, M. kontrimavichusi Piper, MacLean & Christensen, 1982 , M. kuril Healy & Timm, 2000 , M. svetae Piper, MacLean & Christensen, 1982 and M. asiaticus Eisen, 1904 have free spermathaecae, not connected to the oesophagus. Among the species with spermathecae attached to the oesophagus and having a single diverticulum, M. armatus ( Levinsen, 1884) and M. monodiverticulatus Shen, Chen & Xie, 2012 share with M. longidiverticulatus the enlarged chaetae in some preclitellar bundles ventrally or laterally, but here these chaetae are 1.5–2 times longer and thicker than the others, whereas in the new species their size mostly does not reach 1.5 times the size of the other chaetae. Other differences: M. armatus has more chaetae (maximum of 10–12 vs. 6–7), the diverticulum is elongate but not as long as in the new species, the sperm funnel is pear-shaped (vs. 3–7 times longer then wide) and the enlarged chaetae occur in V–VII segments laterally. In M. monodiverticulatus , the spermathecal diverticulum is ear-shaped and the atrial glands are absent. The remaining six species with one spermathecal diverticulum and entally attached spermathecae are M. celticus Southern, 1909 , M. ogloblini Černosvitov, 1928 , M. flavus ( Levinsen, 1884) , M. vivii Timm, 1978 , M. torbeni Christensen & Dózsa-Farkas, 1999 and M. laojunensis Chen, Jiang & Xie, 2016 . In these species, the spermathecal diverticulum is never as long as the one in the new species and there are no enlarged chaetae.

Further observations. An interesting phenomenon should be mentioned: one specimen (paratype slide No.

2620) has three spermathecae ( Fig. 2E ).

Figures

FIGURE 2. Cognettia koreana sp. n. (A, B), Henlea bidiverticulata sp. n. (C) and Mesenchytraeus longidiverticulatus sp. n. (D–F). C. koreana sp. n.: A. Sperm funnel. B. Spermatheca. H. bidiverticulata sp. n.: C. Segments IV–IX (p=pharyngeal glands, s=spermatheca, id=intestinal diverticula, dv=dorsal blood vessel). M. longidiverticulatus sp. n.: D. Spermatheca. E. Segments III–VIII (specimen with three spermatheca 1.s=first spermatheca, 2.s=second spermatheca, 3.s=third spermatheca, pharyngeal glands marked with grey colour). F. Atrium with atrial glands and penial bulb with small penial glands and some accessory copulatory glands. Scale bars 50 μm, C and E 100 μm.

FIGURE 9. Micrographs of Mesenchytraeus longidiverticulatus sp. n. A. Brain. B. Clitellar glands, lateral view. C. Clitellar glands, dorsal view. D. Clitellar glands, ventral view (penial bulbs marked with arrows). E. Head pore (marked with white arrow, brain marked with black arrow). F. Ventral chaetae in V–VII. G. Densely aggregated epidermal glands. H. Coelomocytes. I. Segments X–XII (sperm funnels marked with black arrows, atrial glands marked with white arrows). J–L. Sperm funnel. A–B, G–L in vivo, E fixed, stained, C–D, F fixed, not stained. Scale bars 50 μm. (C–D, paratype slide 2595; F, paratype slide 2596)

FIGURE 10. Micrographs of Mesenchytraeus longidiverticulatus sp. n. A. Segments XI–XIII (sf=sperm funnels, a=atrium, b=bursa, ag=atrial gland). B–D. Penial bulbs (a=atrium, b=bursa, here atrial glands marked with black arrows, *=origin of atrial glands, accessory glands marked with white arrows). E. Sperm rolls in sperm sac. F–J. Spermathecae (a=ampulla, ed=ental duct, ectal duct marked with white arrows, diverticula marked with black arrows). K. Spermathecal ectal duct at orifice with strong cuticular covering. A–E, G–K in vivo, F fixed, not stained. Scale bars 50 μm. (F, holotype).