Enchytraeus irregularis Nielsen & Christensen, 1961

Nagy, Hajnalka, Dózsa-Farkas, Klára & Felföldi, Tamás, 2023, New insights into the Enchytraeus albidus complex (Annelida, Enchytraeidae), with the description of three new species from seashores in Italy and Croatia, European Journal of Taxonomy 870, pp. 107-145 : 27-30

Enchytraeus irregularis Nielsen & Christensen, 1961

Figs 1G , 9 , Tables 1–2

Enchytraeus irregularis Nielsen & Christensen, 1961: 13 .

Enchytraeus irregularis – Hong & Dozsa-Farkas 2018: 81–85, figs. 2–4.

Enchytraeus irregularis – Dózsa-Farkas K. 2019: 81–82, fig. 6.39.1

Material examined

KOREA • 5 specs; Jeollabuk-do, Songcheon-dong ; ID: 262, 906 , slide 573 to 575 ; ELTE .

HUNGARY • 5 specs; Érd; ID 946 , slide 3029 to 3031, 3034 • 2 specs; Tiszalök , slide 2110 to 2111 ; ELTE.

Description

The species was described by Nielsen & Christensen (1961) from compost heap in the Botanical Garden of Copenhagen, Denmark. In 1987, Dózsa-Farkas found it in an earthworm-farm in Tiszalök ( Hungary) and in 2016, in a sewage-sludge compost-bed in Érd ( Hungary). In 2007, individuals of E. irregularis were collected from an earthworm breeding box in house ( Korea, Jeollabuk-do) and a culture was made from these specimens. The results of the latter study were published in Hong & Dózsa-Farkas (2018). Schmelz & Collado (2010) proposed its synonymy with E. capitatus von Bülow, 1957 , but Dózsa-Farkas (2019) disagreed with it. Now we were able to study these specimens using DNA sequencing, so all earlier specimens and some new specimens from Korea and Hungary were studied again morphologically. On the basis of the result of this new study, we give an additional description of this species.

MEASUREMENTS. Body length 14–20 mm, width 540–700 μm at clitellum in vivo (length 9–13 mm and 530–880 μm wide, if fixed), segment number 47–66 (segment number 41–49 in Nielsen & Christensen 1961). Length of the first 12 segments 2.3–3.0 mm, after fixation.

CHAETAE. Straight or slightly curved, formula of 3–2,3: 3–2,3,(4).

CLITELLUM. Saddle-shaped, over XII–XIII (XIV), gland cells small, irregularly scattered ( Fig. 9B ).

HEAD PORE. At 0/1.

BRAIN. About 150 μm long, 1.6 × as long as wide in vivo, with one or two pairs of aggregations of refractile globules ( Fig. 9A ).

OESOPHAGEAL APPENDAGES. Short, outline irregular, thin-walled with single central lumen. All three pairs of primary pharyngeal glands with connection dorsally and ventral lobes.

DORSAL VESSEL. From XIV–XVI, blood faintly red, anterior bifurcation in peristomium ( Fig. 9D ).

COELOMOCYTES. One type, only mucocytes, small, oval or elongate, pear-shaped, 20–29 μm long in vivo, filled with light granules ( Fig. 9C ). Shining hyaline corpuscles also occur but in few numbers.

NEPHRIDIA. Four pairs of nephridia preclitellarly.

SPERM SACS. Paired, well developed and lobed, located in IX–XI ( Fig. 9G ).

SPERM FUNNELS ( Fig. 9G ). 415–730 μm long, 4–7 × as long as wide, about as long as the body diameter in vivo, (270–600 μm long, 2–4 × as long as wide, if fixed), collars slightly wider than funnel.

SPERMATOZOA. About 80–100 μm long, heads about 30 μm in vivo, sperm ducts uniform, about 20 μm wide.

MALE COPULATORY ORGANS. Male glands multiple with larger primary bulb (70–100 μm × 70–100 μm) and 6–8 narrower, long, glandular secondary glands (50–90 μm × 12–14 μm) around male pores ( Fig. 9F–G ). After male copulatory organs pair of oval or squarish glandular structure visible with subdivision (‘accessory sexual glands’) (150–250 μm long, 110–225 μm wide, about 100 μm high, fixed), without external orifice ( Fig. 9F, H–I ). Usually in XIII, directly before the ventral chaetal bundles. In one specimen, visible immediately before male copulatory organs, and in another specimen, where clitellum was from XII to XIV, this organ was found in XV and only on one side (slide no. 573). Now revised again under microscope, so Hong & Dózsa-Farkas (2018): 85 is not correct: “clitellum extended over XII–XV and accessory sexual gland found in XIV” (but correct caption of fig. 3g). In Nielsen & Christensen (1961), location of this organ in front of penial bulb and also in XIII ventrally. These organs mostly larger than male copulatory organ.

SPERMATHECAE. Spermathecal ectal ducts (87–110 μm long), with distinct canals (5–8 μm wide) and ring of glands around ectal orifices. Length of glands about 55–75 μm (fixed). Length of duct without glands proximally 13–25 μm. Duct widens into ampulla proximally (diameter of ampullae about 75–130 μm), which again gradually tapers into short ental ducts, communicating separately with oesophagus. From ampullae anteriorly or laterally arises one large diverticulum (170–220 μm long in vivo, 100–200 μm fixed) filled with spermatozoa ( Fig. 9K–L ). 2–8 mature eggs at a time.

Differential diagnosis

The main differences between this species and the other species investigated by us are the pink blood, and the characteristic large extra sexual glands without external orifice.

For similarities and differences of this species compared to other species of the E. albidus complex, see Table 2 .

Distribution and habitat

Songcheon-dong, Jeollabuk-do, Korea, earthworm breeding box in house.Tiszalök, Hungary, earthworm-farm. Érd, Hungary, sewage-sludge compost bed. This species has unknown origin, only appeared in culture, it has not yet been found in the wild.

Figures

Fig. 1. Schematic drawing of spermathecaeof the specimens studied.A. Enchytraeus adrianensissp. nov. B. E. krumbachi (Čejka, 1913). C–D. E. andrasi sp. nov. E. E. andrasiformis sp. nov. F. E. albidus Henle, 1837. G. E. irregularis Nielsen & Christensen, 1961.

Fig. 9. Micrograph of Enchytraeus irregularis Nielsen & Christensen, 1961. A–H, J, K. In vivo. I, L. Fixed, stained. I. Slide 2110 (ELTE). L. Slide 574 (ELTE). A. Brain (refractile globules marked with arrows). B. Clitellar glands, dorsolateral view. C. Coelomocytes. D. Head, anterior bifurcation of blood vessel with red blood (head pore marked with arrow). E. Chloragogen cells. F. Male copulatory organ (lateral view). G. Sperm funnels. H. Segments XII–XIII (male copulatory organ marked with black arrow, extra sexual gland marked with white arrow). I. Multiple copulatory glands (lateral view, primary gland marked with arrow). J. Extra sexual glands in XIII, ventro-lateral view. K–L. Spermathecae (diverticula marked with arrows). Scale bars: A–B, D–L = 50 μm; C = 20 μm. Abbreviation: s = sperm sacs.