Enchytraeus ohtakai Torii, 2023

Torii, Takaaki, Akagi, Tomohiro, Uchino, Toru & Kobayashi, Tohru, 2023, A new species of Enchytraeus (Enchytraeidae, Clitellata) from sewage sludge of a plum processing plant in Japan, Zootaxa 5254 (2), pp. 245-256 : 250-252

Enchytraeus ohtakai Torii sp. nov.

(Japanese name: Kishu-shiro-himemimizu, new)

( Figures 2 , 3 )

Type material. Holotype: Whole-mounted mature specimen, anterior end, Plum Processing Plant , Minabe-cho, Hidaka-gun, Wakayama Prefecture, Japan, N33.771419, E135.312501, 19 May 2021, T. Akagi (NSMT-An-1881) . Paratypes: 9 whole-mounted mature specimens, anterior end (NSMT-An-1882, 1884, 1885, 1886) and entire (NSMT- An-1883, 1887, 1888, 1889, 1890), same collection data as holotype.

Further material. 20 whole-mounted mature specimens, same collection data as holotype, in the author’s collection.

Etymology. The new species is named in honor of Dr. Akifumi Ohtaka.

Description. Color whitish or pare yellow. Live length 15–17 mm, fixed length 13–15 mm (N=10); first 12 segments (anterior end to clitellum) 3.2–4.0 mm long; width at clitellum 0.75–0.81 mm (N=10). Segments 42–49 (N=10). Chaetal formula 2,3–2,3: 3,(4)–2,3. Lateral preclitellar bundles mostly 3 chaetae, rarely 2 and present in XII. Ventral preclitellar bundles mostly 3 chaetae, rarely 4 and absent in XII. Lateral and ventral postclitellar bundles: 2 to 3 in segments following clitellum. Chaetae straight with ental hook, ectally pointed: 65–110 μm long, 5–10 μm wide, smallest at II, XII and XIII (length 65–77 μm, diameter 5–8 μm) ( Fig. 2E ).

Clitellum in XII–XIII, hyalocytes and granulocytes from level of septum 11/12 to level behind chaetae XIII. Anteriorly and posteriorly a variously extending sleeve of hyaline border cells. Clitellum saddle-shaped, well developed dorsally and laterally, height c. 30 μm, cell diameter c. 15 μm, hyalocytes and granulocytes arranged in reticulate fashion, interrupted mid-ventrally; area without clitellum widest at level of male pores, including the exterior lips ( Fig. 3B ); exclusively granulocytes dorsally of the male exterior lips.

Prostomium rounded ( Fig. 2B ). Head pore present as a longitudinal slit, located at tip of prostomium. Epidermal gland cells inconspicuous. Brain ( Fig. 2A,C ) in I–II, dorsoventrally compressed and narrow, concave posteriorly in living and fixed specimens, postero-lateral region usually with one or two pairs of aggregations of refractile globules; brain approximately 1.5 times as long as wide, length 185–195 μm, posterior width 108–110 μm. Oesophageal appendages a pair of blind-ending tubes in III/IV, c. 180 μm long and 40 μm wide, with common root inserting dorsally in III behind pharyngeal pad, tubes curved, not meandering, not branched, not tapering towards blind end. Pharyngeal pad thickened. Pharyngeal glands in IV–VI, of equal size, with dorsal and ventral lobes, connected dorsally in IV, connected or separate dorsally in V, VI ( Figs. 2A , 3A ). Nephridial anteseptale with funnel only, postseptale bulged, efferent duct short, no terminal vesicle; present at 6/7–9/10 (4 preclitellar pairs, occasionally unpaired) and in postclitellar segments ( Figs. 2A , 3A ). Blood pale reddish. Dorsal blood vessel from XII or XIII, often conspicuous. Anterior bifurcation near prostomium. Coelomocytes flattened, 1.5–4.0 x as long as wide, c. 20–30 μm long, oval or narrowed at one end, filled with pale, conspicuous vesicles ( Fig. 2D ). Transition of oesophagus to intestine gradual, no oesophageal or intestinal diverticula ( Fig. 2B ). Chloragogen cells (chloragocytes) light-brown granulated, beginning from V to backwards, slightly smaller than coelomocytes.

Testes and sperm funnels in XI, ovaries, vasa deferentia, male pores and glands in XII. Seminal vesicle unpaired, in VIII–XI. Mature spermatozoa aligned on top of sperm funnel. Sperm funnel 5–6x as long as wide, variable in shape due to soft tissue of glandular funnel body ( Fig. 3B ). Collar slightly wider or about as wide as funnel body ( Fig. 3B ). Vasa deferentia not extending into segments posterior from XII, in a dense irregular coil that fills almost entire segment of XII, wider entally near sperm funnel than ectally near male pore, ectally passing ventrad between inner face of body wall and primary male glandular ("penial") bulb en route to male pore ( Fig.3B ). Vasa ciliated throughout, without conspicuous musculature.

Male glands multiple and of three distinguishable types, primary "penial" bulb enclosing the male pore, accessory glands arranged roughly in a semicircle around male pore, and further sexual accessory sexual glands ( Fig. 3B ). Penial bulbs not larger than accessory glands. Male pores opening each into a bursa, a lateral invagination of the body wall that is covered by a lip-like fold (bursal fold). Accessory sexual glands present, usually a pair of oval bodies in anterior of XII (9 out of 10 specimens investigated, Fig. 3B ). In one specimen, a single accessory sexual gland present midventrally in XII, near male pores. These organs mostly larger than penial bulbs.

Spermathecae with spherical or sac-like ampulla, ectal duct short, covered with gland cells and abruptly widening into sac-like ampulla; ampulla usually with irregular outline, with one large, dorsal asymmetrical diverticulum; ampullae with separate openings into oesophagus ( Figs. 2A,B , 3A ). Ectal pores at 4/5, in lateral lines, not widened. Ectal duct 95–128 μm long, 11–13 μm wide, covered completely with glands. Ampulla spherical, diameter c. 90–110 μm, wider than ectal duct, with distinct, smooth walls, lumen filled with masses of spermatozoa; ental duct short, connecting laterally with oesophagus ( Fig. 2A,B , 3A ). In subadult specimens, ampulla oval or marginally lobed. No midventral subneural glands observed.

Habitat. The specimens were present in the organic matter at the wastewater treatment facility in Umeta, in organic matter submerged in water with high COD (c. 1,300 mg /L), neutral pH (7.5) and low salt concentration (0.64%). Its natural habitat is still unknown.

Remarks. This new species belongs to the E. albidus group as circumscribed in Schmelz & Collado (2010). Species of this mainly holarctic group live in the marine upper littoral, in brackish water, and in organically enriched habitats such as compost heaps. As Arslan et al. (2018) have pointed out, this group of species is distinguished within the genus by comparatively large body size (length> 10mm, up to 30 mm), high segment number (>40, usually>50), short and tube-like oesophageal appendages, and a large and well-developed male reproductive system that, apart from a male glandular bulb, often includes some smaller accessory glands around the male pores. Furthermore, some species, including the type species Enchytraeus albidus sensu stricto ( Erséus et al. 2019) are distinguished by having more than 3 chaetae per bundle, elongate longitudinal body folds ventrally in the clitellar region that enclose the male pores, and vasa deferentia that extend beyond the clitellar region into posterior segments. Among the E. albidus group, four species, Enchytraeus capitatus von Bülow, 1957 , E. irregularis , Enchytraeus polatdemiri Arslan & Timm (2018) and E. ohtakai sp. nov. share a notable common feature in that their vasa deferentia are restricted within XII, i.e. they do not extend posteriorly beyond the clitellum. Within this subgroup of four species, the following combination of characters is useful to identify the new species: (1) comparatively large body size, (2) each specimen with dorsal and ventral preclitellar bundles of mostly three chaetae, postclitellar bundles of two to three, (3) dorsal blood vessel from XII or XIII, (4) spermathecal ectal duct completely glandular, (5) spermathecal ampulla usually spherical or sac-like, wider than ectal duct, usually with a large diverticulum, (6) always accessory sexual glands in XII, (7) clitellum saddle-shaped( Fig. 3B,C ) and (8) genital field absent. Table 2 gives a comparison of characters among the above-mentioned four species. E. capitatus von Bülow, 1957 and E. irregularis Nielsen & Christensen, 1961 differ from the new species in a more posterior origin of the dorsal blood vessel and in the spermathecal ectal glands, which are located only around the ectal orifice, leaving most of the ectal duct uncovered. E. polatdemiri Arslan & Timm, 2018 differs from the new species in the absence of accessory sexual glands. A further difference, not shown in Table 2 , is the mid-ventral continuity of the clitellum (girdle-shape) at its posterior border ( Arslan et al. 2018). The ventral side of the clitellum is insufficiently known in the other two species, as in most species of the E. albidus group. Further differences of these three species, as listed in Table 2 , may prove to be distinguishing, but they do not apply to all specimens or cannot be evaluated with certainty, mostly due to some intra-specific variablity. For example, the length of the extremely soft-bodied sperm funnel is variable. The taxonomic value of presence or absence of a pair of refractile bodies in the posterior brain region has not yet been assessed sufficiently. Enlarged posterior chaetae in E. capitatus were reported only in the original description but not in the redescriptions of that species ( Nielsen & Christensen 1959, 1961). Schmelz and Collado (2010) suspect that the redescriptions of E. capitatus are based on different species. It is further worth noting that the accessory sexual glands in E. irregularis are distributed differently in the original description ( Nielsen & Christensen 1961) and in the only redescription ( Hong & Dózsa-Farkas 2018; Dózsa-Farkas 2019) that is so far available: originally, these glands are said to be in XII or in XII and XIII, while in the material underlying the redescription these glands are only found in XIII. Evidently, E. capitatus and E. irregularis need further investigations; their synonymy, however, as proposed in Schmelz & Collado (2010), was correctly rejected in Hong & Dózsa-Farkas (2018), based on the chaetal distribution and presence/absence of accessory sexual glands.

Figures

FIGURE 2. Enchytraeus ohtakai sp. nov. A. Anterior body region (12 segments) of a mature specimen, lateral view, coelomocytes omitted, fragment of holotype (NSMT-An-1881). B. Spermatheca. C. Brain, white arrows indicate refractile granules. D. Coelomocytes. E. Lateral chaetae. A–D from living specimen, E from fixed specimen.

FIGURE 3. Enchytraeus ohtakai sp. nov. A. Segments V–VII, dorsal view. B. Segments XI–XIII, ventral view. Drawing from living paratype specimen (NSMT-AN-1882).