Enchytraeus polatdemiri Arslan & Timm, 2018

Arslan, Naime, Timm, Tarmo, Rojo, Verónica, Vizcaíno, Antón & Schmelz, Rüdiger M., 2018, A new species of Enchytraeus (Enchytraeidae, Oligochaeta) from the profundal of Lake Van, the world's largest soda Lake (Turkey, East Anatolia), Zootaxa 4382 (2), pp. 367-380 : 372-375

publication ID	https://doi.org/ 10.11646/zootaxa.4382.2.8
publication LSID	lsid:zoobank.org:pub:A1023C65-5905-405B-99E2-57A849AB8C8F
DOI	https://doi.org/10.5281/zenodo.5961021
persistent identifier	https://treatment.plazi.org/id/03C68788-8571-FFCA-FF19-007AC12F9C2D
treatment provided by	Plazi
scientific name	Enchytraeus polatdemiri Arslan & Timm
status	sp. nov.

Treatment

Enchytraeus polatdemiri Arslan & Timm , sp. nov.

( Figures 2 View FIGURE 2 , 3 View FIGURE 3 )

Holotype. ESOGU-Epolatdemiri-01, adult specimen, unstained whole mount, anterior end (14 segments), mounted between two coverslips, posterior end processed for DNA sequencing (specimen ID EP2, see Table 2, Fig. 4 View FIGURE 4 ), Turkey, Lake Van, N38º21.466' E043º04.345', profundal sediment at 50 m depth, station 3 ( Table 1), 16.06.2012, N. Arslan. GoogleMaps

Paratypes. ESOGU-Epolatdemiri-02–04, 3 adult and subadult specimens, same data as holotype GoogleMaps . ESOGU- Epolatdemiri-05–08, 4 adult and subadult specimens, processed as holotype, N38º36.502' E043º07.343', profundal sediment at 36 m depth, station 14 ( Table 1), 16.6.2012, N. Arslan. ESOGU-Epolatdemiri-09, 9 specimens, 4 adult, 3 subadult, 2 juvenile, unstained whole mounts on one slide, Station 24, 14.10.2011, N. Arslan ( Table 1). ESOGU- Epolatdemiri-10, 9 specimens, 5 adult, 2 subadult, 2 juvenile, unstained whole mounts on one slide, Station 2 ( Table 1), 16.6.2012, N. Arslan. ESOGU-Epolatdemiri-11, 4 specimens, 3 adult, 1 subadult, slightly stained, partly fragmented, Station 32, 16.06.2012, N. Arslan ( Table 1). VLS-S4258, 3 specimens, 1 adult, 2 subadult, stained whole mounts on one slide, Station 20 ( Table 1), 19.8.2011, N. Arslan. VLS-S4 259, 8 specimens, 3 adult, 5 subadult, stained whole mounts on one slide, Station 21, 14.10.2011, N. Arslan ( Table 1).

Further material. ESOGU-Epolatdemiri-12, Station 18, ca. 8 specimens in 96% ethanol, partly fragmented, subadult and juvenile, 14.10.2011, N. Arslan. ESOGU-Epolatdemiri-13, Station 20, 10 specimens in 96% ethanol, subadult and juvenile, 14.10.2011, N. Arslan. ESOGU-Epolatdemiri-14, Station 21, 6 specimens in 96% ethanol, subadult and juvenile, 14.10.2011, N. Arslan. ESOGU-Epolatdemiri-15, Station 3, ca. 7 specimens in 96% ethanol, partly fragmented, subadult and juvenile, 16.06.2012, N. Arslan. ESOGU-Epolatdemiri-16, Station 14, ca. 3 specimens in 96% ethanol, partly fragmented, subadult and juvenile, 16.06.2012, N. Arslan. ESOGU-Epolatdemiri- 17, Station 24, multiple fragments in 96% ethanol, not counted, 16.06.2012, N. Arslan. VLS-S4263, 1 specimen, sagittal sections on 2 slides, Station 24, 14.10.2011, N. Arslan. VLS-S4264, 1 specimen, sagittal sections on 2 slides, Station 24, 14.10.2011, N. Arslan. VLS-S4260, 1 specimen, horizontal sections on 2 slides, Station 23, 14.10.2011, N. Arslan. VLS-S4261, 1 specimen, horizontal sections on 3 slides, Station 23, 14.10.2011, N. Arslan.

Etymology. The species is named in memory of Şevket Polatdemir (1940-1997), Prof. Dr. Naime Arslan's father, an outstanding person.

Description. Body length 7.5–11 mm, diameter c. 0.4 mm, in clitellar region c. 0.5 mm (0.32–0.38 mm at V, 0.41–0.58 mm at XII, 0.42–0.49 mm at XX, N=10). Segment number 40–55 (N=10). Chaetae 2 or 3 per bundle, rarely more (6 in 1 bundle of 1 specimen, Fig. 2A View FIGURE 2 , segment VIL), occasionally 1 or 0; at XII absent ventrally, present laterally, 2 per bundle. Chaetal formula 2,3 – 2,3: 2,3 – 2,3. Lateral preclitellar bundles: 2 and 3 irregularly alternating, some specimens with mostly 2, others with mostly 3 chaetae, or intermediate states. Ventral preclitellar bundles: mostly 3 chaetae, 2 chaetae near clitellum (X, XI). Lateral and ventral postclitellar bundles: 2 in segments following clitellum, caudad increasingly 3. Chaetae straight with ental hook, ectally pointed: 80–110 µm long, 6–7 µm wide, smallest at II, XII and XIII (length 70–90 µm, diameter 3.5–5 µm). Caudal chaetae not or only slightly enlarged. Epidermal gland cells not seen.

Brain c. 1.5x as long as wide, rounded posteriorly, sides slightly merging anteriad. Oesophageal appendages a pair of blind-ending tubes in III/IV, c. 140 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 glands in IV–VI, of equal size, with dorsal and ventral lobes, connected dorsally in IV, connected or separate dorsally in V, VI. Nephridial anteseptale with funnel only, postseptale bulged, efferent duct short, no terminal vesicle; present at 6/7–9/10 (4 preclitellar pairs) and in postclitellar segments. Dorsal blood vessel from XIII, XIV, (XV), often conspicuous ( Fig. 3B View FIGURE 3 ). Anterior bifurcation near prostomium. Coelomocytes flattened, 3x as long as wide, c. 20–30 µm long, oval or narrowed at one end, texture not ascertained.

Clitellum in XII–XIII, hyalocytes and granulocytes from level of septum 11/12 to level of chaetae XIII. Anteriorly and posteriorly a variously extending sleeve of hyaline border cells ( Fig. 2A,E View FIGURE 2 : cb). Clitellum welldeveloped dorsally and laterally, height c. 30 µm, cell diameter c. 15 µm, hyalocytes and granulocytes arranged in reticulate fashion, mostly interrupted mid-ventrally, continuous at posterior border; area without clitellum widest at level of male pores, including the exterior lips ( Fig. 2E View FIGURE 2 : ml); exclusively granulocytes at ventro-lateral borders and dorsally of the male exterior lips.

Testes and sperm funnels in XI, ovaries, vasa deferentia, male pores and glands in XII. Seminal vesicle unpaired, in X–XI. Mature spermatozoa aligned on top of sperm funnel; length of sperm heads not measured. Sperm funnel c. 5x as long as wide, variable in shape due to soft tissue of glandular funnel body. Collar about as wide as funnel body. Vasa deferentia occasionally extending into posterior segments (XIII: 2 specimens; XIV: 1 specimen; XV: 1 specimen; N=38), but mostly confined to XII in a dense irregular coil that fills almost the entire segment; wider entally near sperm funnel ( Fig. 3C View FIGURE 3 : en) than ectally near male pore ( Fig. 3C View FIGURE 3 : ec), ciliated throughout, ectally passing ventrad between inner face of body wall and primary male glandular bulb en route to male pore. Male glands multiple: one large rounded primary bulb near male pore, and ca. 9 smaller secondary papillae medially, arranged roughly in a semicircle around male pore and primary bulb ( Figs 2D View FIGURE 2 , 3C,D View FIGURE 3 ). Male pores opening each into a bursa, a lateral invagination of the body wall that is covered by a lip-like fold (bursal fold) directed mediad ( Fig. 2E View FIGURE 2 : ml). Spermathecae with ectal duct, ampulla, no diverticula, separate openings into esophagus. Ectal pores at 4/5, slightly below lateral lines, not widened. Ectal duct slightly longer than wide (80–85 µm by 55–80 µm), covered completely with glands, canal widening entad, lined with cuticle; ampulla spherical, diameter c. 120–150 µm, wider than ectal duct, with distinct, smooth walls, lumen completely filled with masses of spermatozoa; ental duct short, connecting laterally with esophagus.

Remarks. Enchytraeus polatdemiri sp. nov. belongs to the Enchytraeus albidus group as circumscribed in Schmelz & Collado (2010). 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 ("penial") bulb, often includes a number of smaller accessory glands around the male pores. Furthermore, several species, among them the common and widespread Enchytraeus albidus Henle, 1837 , have 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. Species of this mainly holarctic group live in the marine upper littoral, in brackish water, and in organically enriched habitats such as compost heaps. Apart from E. albidus it currently includes E. capitatus von Bülow, 1957 , E. kincaidi Eisen, 1904 , E. mediterraneus Michaelsen, 1926 , E. multiannulatus Altman, 1936 , and E. multiannulatoides Altman, 1936 , together with a number of junior synonyms.

Within this group, E. polatdemiri sp. nov. is distinguished by the following combination of characters: (1) Comparatively small body size, (2) each specimen with bundles of two and three chaetae in varying arrangement, (3) vasa deferentia usually not extending beyond clitellum, and if so, only 1–2 segments, (4) spermathecal ectal duct completely glandular, (5) spermathecal ampulla spherical, wider than ectal duct, without diverticula. Further possibly distinguishing characters refer presently to E. albidus only, because they are still unkown in the other species: (6) clitellum ventrally almost absent, with a peculiar distribution of granular cells ( Fig. 2E View FIGURE 2 ), (7) absence of a genital field, and (8) bursal folds not elongate.

Among the six above-mentioned species of the E. albidus -group, only E. albidus has spermathecae that, at least in some specimens, are similar to those in E. polatdemiri sp. nov.: ectal duct completely glandular, ampulla spherical, no diverticulum (comp. Nielsen & Christensen 1959, Fig. 97). In the remaining five species, spermathecal ectal glands are absent or reduced to a crown around the ectal pore, and/or one or two diverticula are present. E. albidus differs in several characters from E. polatdemiri sp. nov.: more than 3 chaetae per bundle (up to 6 ventrally), bursal folds elongate, genital field present, vasa deferentia extending beyond clitellum ( Schmelz & Collado 2010). Furthermore, specimens are usually much larger and up to 3 cm long.

However, the species is highly variable and the evaluation of taxonomic characters is not straightforward. To give examples: Spermathecae are reported that include forms that are common for the other species ( Nielsen & Christensen 1959). For example, all specimens of E. albidus sequenced in this study had a spermatheca with a large, asymmetrical dorsal diverticulum and an incomplete glandular coverage of the ectal duct (comp. Nielsen & Christensen 1959: 96). It is also unknown whether the posterior extension of the vas deferens applies to all specimens without exception; in addition, some specimens of the new species share this character state. Furthermore, E. sabulosus Southern, 1906 , tentatively included in E. albidus by Nielsen and Christensen (1959), has also a maximum of 3 chaetae per bundle and a body size (10–15 mm when alive) comparable to that of the new species. Finally, there is molecular evidence that E. albidus consists of more than one species ( Erséus & Gustafsson 2009).

On this background of taxonomic uncertainty is was advantageous to have a second dataset, i.e. molecular evidence, to evaluate the taxonomic status of the Lake Van population.

Molecular analysis. The individual gene trees of COI and H3, as well as the combined phylogenetic analysis of both tree, recovered Enchytraeus polatdemiri as a monophyletic group within the genus Enchytraeus , with the highest support (pp = 1) ( Fig. 4 View FIGURE 4 ). In the concatenated tree, E. polatdemiri forms a well-supported sister group to the clade comprising all E. albidus specimens ( Fig. 4C View FIGURE 4 ), whereas in the individual gene trees, relationships between E. polatdemiri sp. nov., E. albidus , E. japonensis (only COI), and E. bulbosus are poorly resolved ( Fig. 4A,B View FIGURE 4 ).

The maximum uncorrected p-distance between the specimens of Enchytraeus polatdemiri sp. nov. was 1.0 % for the COI gene, while H3 sequences were identical in this group ( Tables 3 and 4). Average p-distances for COI between Enchytraeus polatdemiri sp. nov. and the other congeneric species included in the analysis ranged from 14.5 % with E. albidus (excluding the specimen from Denmark) to 19.5 % with E. japonensis ( Table 3). Average H3 distances were substantially lower, ranging from 5.4 % with E. albidus to 10.5 % with E. bulbosus ( Table 4). A potential barcode gap was found for COI pairwise genetic distances between 5 % and 11 % ( Fig. 5 View FIGURE 5 ). ABGD’s initial partition delineated seven MOTUs, which are those indicated in Table 3. H3 pairwise distances did not show a clear barcode gap.