Mesenchytraeus globiferus, Dózsa-Farkas & Nagy & Felföldi & Hong, 2022

Dózsa-Farkas, Klára, Nagy, Hajnalka, Felföldi, Tamás & Hong, Yong, 2022, Four new enchytraeid species (Enchytraeidae, Annelida) from a Korean mountain (Jeoksangsan), Zootaxa 5094 (2), pp. 234-260 : 247-250

Mesenchytraeus globiferus sp. n.

( Figures 2E , 10–12 )

Type material. Holotype: NIBRIV0000886170, slide No. 3111a+b+c, adult, stained specimen. Type locality: Jeoksangsan , Jeoksang-myeon, Muju-gun, Jeollabuk-do, Korea, soil and litter layers of Quercus serrata and mixed forests, N 35˚56′55.02″, E 127˚40′41.99″, 476 m asl, 06.11.2019 . Paratypes: NIBRIV0000886171, slide No. 2910a+b (last 38 segments, 5.9 mm, for DNA analysis No. 1423) and NIBRIV0000886172, slide No. 2967, adult, stained, mounted specimens, from type locality. P.138.1–P.138.12., slide No. 2879, 2901a,b, 2945a,b, 2968a,b, 3105a-d, 3107a,b, 3109a,b, 3110a,b, 3112a,b, 3113a.b, 3114a-c, adult, stained specimen, whole mounted. P.138.13., 5 adult and 2 juvenile specimens in 70% ethanol.

Further material examined. 3 specimens, ruined after preservation

Etymology. The species is named after the characteristic globular everted bursae [globiferus = globe-bearing (Latin)].

Diagnosis. The new species can be recognized by the following combination of characters: (1) large worms (27.5–37 mm long and about 1 mm at clitellum in vivo, 13–21.6 mm long when fixed), 70–94 segments, colour yellowish, dark brown pigment in head region; (2) chaetae sigmoid with nodulus, maximum 4–5 per bundle, in V– VII ventrally only 2–3 slightly enlarged chaetae, the size from V–XI ventrally about the same. Postclitellarly more chaetae in one bundle, maximum number may be 6 (7–8) ventrally and 4–5 (6) laterally; (3) clitellum girdle-shaped; (4) five preclitellar pairs of nephridia; (5) dorsal blood vessel from XXII–XXVIII, blood light pink; (6) two pairs of primary and 4 pairs of secondary pharyngeal glands, lobed, not connected dorsally; (7) sperm funnel 670–880 µm long and 4–8 times longer than wide in vivo, sperm ductus loosely coiled in XII–XIII, diameter 30–40 µm, fixed. Atrium 300–550 µm long, maximum width 120–160 µm (fixed) with 6–7 large atrial glands; (8) the bursa mostly everted as a large ball (diameter 500–950 µm, fixed). The atrium lies in the bursa and some large multicellular penial glands fill the cavity of the bursa; (9) the part of the sperm duct after the atrium is very long and protrudes far from the bursa (true penis); (10) sperm sacs and egg sac may extend into XXIII–XXIV; (11) spermathecal ampullae proximally fused and attached to the oesophagus in V. The ectal ducts different lengths (320–550 µm long and 60 µm wide, fixed). Ectally with a large ectal gland, surrounded by a large cavity, the aperture is large.

Description. Large enchytraeid worm. Colour yellowish, prostomium dark-brown by pigmentation ( Fig. 10A ); dorsal side of first few segments light brown mottled ( Fig. 10B ). Holotype 17.6 mm long, 920 µm wide at VIII and 1600 µm at clitellum (fixed), segment number 90. Body lengths of paratypes 27.5–37 mm, width 780–1000 µm at VIII and 825–1300 µm at clitellum in vivo; lengths of fixed specimens 13–21.6 mm, width 640–930 µm at VIII and 700–1050 µm at clitellum. Segments (62)–70–94. Strong external segmentation at body end. Chaetae sigmoid with nodulus. Chaetal formula: 2,3–3, (2),4,5,(6): 4,5,3,2– 3,4,5,6, (7,8),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. In II–IV mostly 3–5 chaetae per bundle ventrally ( Fig. 10B ) (about 90–145 × 8 µm). In V–XI only 2–3 larger and stronger chaetae (140–190 × 12 µm), in X–XI the length of the chaetae slightly smaller (150–170 × 12 µm) ( Fig. 10C ). Behind clitellum, chaetae slightly smaller and thinner (135–150 × 10 µm). Chaetae of lateral bundles slightly smaller and thinner than ventrals. At the body end, longest chaetae measuring 120–160 × 8-9 µm ( Fig. 10D ). Chaetae in XII absent. Head pore at 0/I, a large transverse slit ( Fig. 10A ). Clitellum girdle–shaped in XII–XIII, gland cells small, in reticulate pattern. Thickness of body wall about 120–140 µm, cuticle <1 µm.

Brain ( Fig. 10H ) incised anteriorly and slightly convex posteriorly, wider than long (e.g. 125 µm long and 165 µm wide, fixed). Two pairs of primary pharyngeal glands (in 4/5–5/6), not united dorsally, and four (in one case five pairs) of secondary pharyngeal glands in V –VIII ( IX); the glands lobed ( Fig. 10I ). Yellow-brownish chloragocytes from IV, about 30–45 µm long, fixed. Dorsal blood vessel from XXII–XXVIII, anterior bifurcation in I, blood light pink. 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 ( Fig. 10J ). Oesophageal and intestinal appendages or diverticula absent. Coelomocytes were not observable. Sperm sac extending backwards to XXIII–XXIV, egg sac to XIV –XXV. In one specimen the sperm bundles were measurable, 230 µm long, the heads clumped only at one end and 50 µm long ( Fig. 10M ). Sperm funnel ( Figs 10K–L ) about 670–880 µm long and 4–8 times longer than wide in vivo (425–970 µm long, and 3–5.5 times longer than wide, when fixed). Sperm duct long, loosely coiled in XII–XIII, diameter 30–40 µm, fixed. Atrium ( Fig. 8D ) 300–550 µm long, maximum width 120–160 µm, here joined by 6-7 large atrial glands (prostate glands), usually 230 – 300 µm long ( Figs 11A, C ) .

Among enchytraeids, the male copulatory organ shows the most complex structure in the genus Mesenchytraeus ( Eisen 1904) . In this species the eversible pouch (= bursa after Schmelz 2003) mostly appears as a huge projected ball ( Figs 11A–D ), diameter about 500–950 µm, in fixed specimens. Atrium and atrial glands lie inside this projection (i.e., the everted bursa), the atrial glands only partially. Near the atrium there are large multicellular ‘penial’ glands (perhaps 3–4, number difficult to determine) which fill the cavity of the bursa ( Fig. 11D ). A special feature is that the most distal part of the sperm duct after the atrium is very long and protrudes far outside the bursa (400–620 µm long and 50–110 µm wide, fixed) ( Fig. 11C,E ). The everted bursa was formerly called penis, but according to its usual structure it is not able to deliver sperm directly to the spermatheca, so it is not a penetratory organ but serves as clasper, and most of the secretions of the adjoining glands are probably adhesive slimes ( Schmelz 2003), as we can see, e.g., in Mesenchytraeus calyx (Dózsa-Farkas et al. 2015, p.188, Fig. 11A ). However we believe that in this species the male copulatory organ actually functions as a penis, because the diameter of the spermathecal opening (about 220 µm long) ( Figs 12C–D ) is approximately equal to the diameter of the protruding long sperm duct, named here as penis (width 70–90 µm on average, maximum width 110 µm, narrower at apex). Subneural glands absent.

The spermathecae ( Figs 2 , 12E–I ) were difficult to see due to highly stained pharyngeal glands, and were therefore partially removed from dissected individuals. Ectal ducts of different length in the same animal, one side mostly shorter, 320–450 µm; length 436–550 µm on the other side, width 40–60 µm, fixed. Ectally it opens into a spacious “capsule” containing a large gland ( Fig. 11F,G ). This, as mentioned above, opens with a wide aperture to the outside ( Fig. 12C,D ). The ectal duct projects deeply into the ampulla, which has two elongate diverticula projecting backwards and lining ectal duct on opposite sides. The proximal parts of the two ampullae are fused and attached to the oesophagus in V, and probably also connected with it (the connection was not observable) .

Distribution and habitat. Only known from type locality (Site 1): Jeoksangsan, Jeoksang-myeon, Muju-gun, Jeollabuk-do, Korea, soil and litter layers of Quercus serrata and mixed forests, N 35˚56′55.02″, E 127˚40′41.99″, 476 m asl.

Differential diagnosis. The Mesenchytraeus globiferus sp. n. differs from all known Mesenchytraeus species in the form of the spermatheca (large ectal gland, surrounded by a large cavity, and the fusion of the two ampullae) and by the large spherical eversible bursa with elongate, from the bursa protruding sperm duct, the bursa. The morphological separation was supported also with the molecular results.

Figures

FIGURE 2. A. Decimodrilus bulbosus sp. n. Spermathecae. B–C. Fridericia sphaericoides sp. n. B. Spermatheca. C. Coelomocytes. D–E. Fridericia jeoksangsaniensis sp. n. D. Spermathecae. E. Coelomocytes. F. Mesenchytraeus globiferus sp. n. Spermathecae.

FIGURE 8. Micrographs of Fridericia jeoksangsaniensis sp. n. A–B. Clitellar glands, dorsal view. C–D. Clitellar glands, ventro-lateral view (m=male copulatory organs, in ventral midline between bursal slits almost exclusively granular gland cells, marked with arrow). E–F. Coelomocytes. G. Forepart of oesophageal appendage with many branches. H. End part of oesophageal appendage with many branches. I. Sperm funnel. J. Male copulatory organs. K. Field of epidermal glands (arrows) surrounding orifice of spermathecae (not seen here), ventral view. L, M. Spermathecae. A, C–E, G–I, K–L in vivo, B, F, J, M fixed, stained. Scale bars 50 μm, L 200 μm.

FIGURE 10. Micrographs of Mesenchytraeus globiferus sp. n. A. Head with brown pigmentation and head pore. B. Brown pigmentation in epidermis, four chaetae in the ventral bundle of segment II. C. Two larger chaetae in ventral bundles in segments VIII–IX. D. Chaetae in bundles near posterior body end, latero-ventral view. E. Body from head to segment XIV with two everted bursae, lateral view. F. Two everted bursae, ventral view. G. Dorsally dissected and stained specimens, fixed with minutia-needle. H. Brain. I. Pharyngeal glands (V–VIII, spermathecal ectal glands marked with arrow). J. Nephridia. K,L. Sperm funnel. M. Sperm bundles. A–C, E, K in vivo, D, G–J, L–M fixed, stained, F fixed, not stained. Holotype F. Scale bars 50 μm, E–G 500 μm.

FIGURE 11. Micrographs of Mesenchytraeus globiferus sp. n. A. Everted bursa, atrial glands everted as well. B. Two atrial glands. C. cut-off and opened everted bursa and atrial glands (marked with black arrows) and penial glands (marked with white arrows). D. Cut-off everted bursa (a=atrium, penial glands marked with arrows). E. Long end part of sperm duct „penis”. F–G. Spermathecal ectal capsula with glands (g=gland, d=ectal duct). A–B, F–G in vivo, C–E fixed, stained. Holotype C, E. Scale bars 50 μm, A 500 μm, B 200 μm.

FIGURE 12. Micrographs of Mesenchytraeus globiferus sp. n. A. Spermatheca (eg=ectal glands, a=ampulla, ectal duct marked with arrow). B. Spermathecal ampulla (marked with black arrow) with two diverticula (marked with white arrows). C,D. Spermathecal ectal opening from outside. E,F. Spermathecae (eg=ectal glands, ampullae with diverticula marked with black arrows). G. Two spermathecae (eg=ectal glands, fused distal part of ampullae marked with white arrow, the ampullae marked with black arrows). H,I. Spermathecal ampullae with diverticula. A–C in vivo, D–I fixed, stained. Scale bars 50 μm.