Enchytraeus albellus Klinth, Erseus and Rota 2019
Creators: name: Erséus, Christer
name: Klinth, Mårten J.
name: Rota, Emilia
name: De Wit, Pierre
name: Gustafsson, Daniel R.
name: Martinsson, Svante
Publisher: name: Zenodo
Year: 2019
Subjects: Biodiversity
Taxonomy
Animalia
Annelida
Clitellata
Enchytraeida
Enchytraeidae
Enchytraeus
Enchytraeus albellus

description: Etymology Latin albellus, diminutive of albus, i.e., whitish.   
 Diagnosis Several chaetal bundles with more than three chaetae; sperm funnels 2–4 times longer than wide; vasa deferentia tripartite: ental and ectal sections thin-walled, middle section thick-walled, all parts ciliated; penial bulbs larger than accessory glands; spermathecae sometimes with one diverticulum.   
 External characters Color white. Length of first 21–54 segments> 3–10 mm (fixed, amputated specimens); first 12   
segments (anterior end to clitellum) 1.6–2.7 mm long; width at clitellum 0.51–0.72 mm. Chaetae straight or slightly curved. Lateral bundles with 3–4 chaetae anterior to clitellum, 0–2 in XII, 2–3(4) chaetae in postclitellar segments. Ventral bundles with 3–5 chaetae anterior to clitellum, missing in XII, 2–3(4) chaetae in postclitellar segments. Chaetae longest in ventral preclitellar bundles (IV–XI) and some lateral bundles close to XII, measuring 65–115 by 5–8 μm. Clitellum extending over XII–½XIII or –¾XIII. Head pore between prostomium and peristomium. Epidermis with transverse rows of gland cells.  
 Internal characters Coelomocytes numerous, 10–25 μm long, round, oval, or spindle-shaped, granulated and with distinct nucleus. Paired pharyngeal glands present in IV, V, and VI. All pairs with secondary lobes, dorsal connections between the pairs uncertain. Esophageal appendages (peptonephridia) extending from dorsal wall of esophagus in III. Dorsal vessel originating in XIVor XV. Nephridia in 6/7–9/10 and from 13/ 14 to 14/15 at least, about 75–80 μm long, anteseptale with funnel only, postseptale oval tapering into posteroventral efferent duct, in one specimen nephridia observed also from 30/ 31 to 49/50. Brain truncate posteriorly.   
Male genitalia paired. Testes in XI, each surrounded by masses of cells at different stages of spermatogenesis within peritoneal sac; testis sacs bulging into IX. Sperm funnels in XI, 400–530 μm long, 135–235 μm widest, making them about 2–4 times longer than wide, funnels tapering towards vasa deferentia (Fig. 11a). Vasa irregularly coiled in XII– XXVIII, tripartite, ental and ectal parts thinner and thin-walled, 25–35(45) μm wide with 2.5–5 μm thick wall, middle part wider (30–45(65) μm) with thicker wall (10–20 μm) (Figs. 11b–c). All parts ciliated, without conspicuous musculature. No abrupt transition between thin- and thick-walled parts and the different parts seem indistinguishable in some specimens, possibly becoming clearer with maturation. Vasa seemingly not penetrating penial bulbs. Ventral surface of XII with invaginations creating two recesses with overhanging lips. Penial bulbs compact, round, 70–120 μm in diameter, surrounded by accessory glands much smaller in size (Fig. 11d). Ovaries in XII. About one to four mature eggs present at a time.  
Spermathecae in V. Pore at lateral line. Ectal duct short, abruptly widening into sac-like ampulla (Fig. 11e) entally connected with lateral side of esophagus. Ampulla usually with irregular outline, sometimes with one, usually dorsal diverticulum. Sperm in lumen of ampulla, heads of spermatozoa embedded in wall of ental part of ampulla, forming aggregates. Spermathecae 125–335 μm long, (40)100–215 μm wide at widest part of ampulla. Gland cells surrounding ectal duct, forming compact mass 65–120 μm in diameter at its widest part; in some (possibly all) specimens, a short, ental part of duct not covered by these cells. No obvious midventral subneural glands observed.  
 Remarks Despite a thorough literature search, we have been unable to locate any previous reference to, or description of, the E. albellus morphotype. E. albellus is genetically well separated from our specimens of E. albidus s. str. in both the COI (Fig. 3a) and ITS2 (Fig. 3c) regions. In addition, there are several morphological characters that distinguish E. albellus from all other species in the E. albidus species complex.   
 As noted above, E. albellus is morphologically similar to E. albidus s. str. and to our E. cf. krumbachi in having long, tripartite, and partly very wide and thick-walled vasa deferentia, which occupy several segments beyond the clitellum; E. moebii also has long vasa, but in this species the vasa are uniformly narrow.   
 E. albellus differs from E. albidus s. str. in the following characters: (1) the separation of the vasa into thick- and thin-walled sections is not as clear-cut in E. albidus as in E. albellus; (2) the penial bulbs are not much larger than the accessory glands in E. albidus, but the penial bulbs are distinctly larger than the accessory glands in E. albellus (compare Figs. 6 and 11d); and (3) the sperm funnels are 5–7 times longer than wide in E. albidus, compared to 2–4 times for E. albellus.   
 E. albellus can be separated from E. cf. krumbachi in having a dorsal diverticulum on the spermatheca, cilia in all parts of the vasa, and more than two chaetae per bundle in postclitellar segments (Table 3).   
 Geographical distribution Sweden, Norway, and Greenland. This species is represented in BOLD by BINs: AAT8961 and ACV8067.   
 Habitat In seashores, both above and below the high-water line, and with a clear tendency to go lower into the intertidal zone than E. albidus and E. moebii; occurs in decaying organic material on beaches, but is common also in rather clean intertidal sand and gravel.
description: Published as part of Erséus, Christer, Klinth, Mårten J., Rota, Emilia, De Wit, Pierre, Gustafsson, Daniel R. & Martinsson, Svante, 2019, The popular model annelid Enchytraeus albidus is only one species in a complex of seashore white worms (Clitellata, Enchytraeidae), pp. 105-133 in Organisms Diversity & Evolution (New York, N. Y.) (New York, N. Y.) 19 (2) on pages 124-126, DOI: 10.1007/s13127-019-00402-6, http://zenodo.org/record/13344959