Varichaetadrilus vestibulatus Cui & Wang, 2009, n. sp.
Creators: name: Cui, Yongde
name: Wang, Hongzhu
Publisher: name: Zenodo
Year: 2009
Subjects: Biodiversity
Taxonomy
Animalia
Annelida
Clitellata
Enchytraeida
Randiellidae
Varichaetadrilus
Varichaetadrilus vestibulatus

description: Varichaetadrilus vestibulatus n. sp.
Holotype: IHB YAN 20030201a, whole-mounted specimen.
Type locality: Northeast of Jianshan (24º36΄0 3΄ N, 102º51΄14΄ E) in Fuxian Lake, eastern Yunnan Province, China; depth 97 m, bottom temperature 13.5°C, dissolved oxygen at bottom 5.6 mg /L, total nitrogen in water 0.193 mg /L, total phosphorus in water 0.018 mg /L, fine clay; 14 Feb 2003, coll. Y. Cui.
Paratypes: IHB YAN 20030205a (Paratype-a) ─ 20030205b (Paratype-b), whole-mounted, two mature specimens from east of Lichang (24º32΄0 4΄ N, 102º51΄43΄ E) in Fuxian Lake; depth 113 m, bottom temperature 13.5°C, dissolved oxygen at bottom 5.2 mg /L, total nitrogen in water 0.195 mg /L, total phosphorus in water 0.024 mg /L, fine clay; 14 Feb 2003, coll. Y. Cui.
Etymology: The specific name “ vestibulatus ” is Latin for “vestibule”, and refers to the pear-shaped vestibule in spermathecal duct.
Description: Length 11.3–30.0 mm (Holotype: 30.0 mm), width at XII about 0.6 mm, with 58–140 segments (Holotype: 140). Clitellum inconspicuous.
Dorsal chaetae (Fig. 1 A) of II–VII (II–III in paratype-a) bifid only, 3–8 per bundle, 115–140 µm long, 2.5–3.0 µm thick, with upper prong twice as long as and thicker than lower, nodulus distal. Dorsals of VIII–X (IV–IX in paratype-a) 3–5 hairs and 5–8 bifids per bundle; hairs slender and smooth, 250–300 µm long, 2.0 µm thick basally; bifids (Fig. 1 C) 110–135 µm long, 2.0–2.5 µm thick, prongs almost parallel, upper one slightly longer than, or as long as lower. Dorsals (Fig. 1 D) of XI–XII (X–XI in paratype-a) bifid only, 5–6 per bundle, shorter and thicker than those in II–VII, with upper prong usually curved, and slightly longer than, lower. From XIII (XII in paratype-a) onwards, dorsals 2–5 hairs and 3–6 bifids per bundle, shorter and thinner than those of VIII–X, hairs 200–240 µm long, bifids (Fig. 1 A) 100–115 µm long, with prongs similar to those of VIII–X, simple-pointed chaetae (Fig. 1 B) sometimes present. Ventral chaetae (Fig. 1 E, F) bifid, 6–8 per bundle anteriorly, 100–140 µm long, 2.0–3.0 µm thick, with prongs similar to those of dorsals in II–VII; 3–5 per bundle posteriorly, 90–110 µm long, 1.8–2.0 µm thick, with upper prong longer and thinner than lower. Ventral chaetae absent in IX. Spermathecal chaetae (Fig. 2 A, sc; Fig. 2 B) one per bundle in mid-X (mid-IX in paratype-a), entally embedded in glandular sacs, about 130 µm long, 4.0 µm thick, ental part curved and ectal part grooved. Penial chaetae (Fig. 1 G) 1–2 per bundle in postero-XI (postero-X in paratype-a), 75–82 µm long, 2.8 µm thick, with upper prong slightly longer and thinner than lower, without nodulus. Male pores paired in line with ventral chaetae, posterior to middle of XI (mid-X in paratype-a). Spermathecal pores paired in line with ventral chaetae in mid-X (mid-IX in paratype-a), immediately anterior to spermathecal chaeta.
Pharyngeal glands in II–III. Chloragogen cells from VI (V in paratype-a) onwards. No coelomocytes. Male genitalia (Fig. 1 H) paired in X–XII (IX–XI in paratype-a). Vas deferens (Fig. 1 H, vd) up to 35 µm wide, shorter than atrium, although posterior part unclear; entering apical end of atrium. Atrium (Fig. 1 H, st) extending to XII (XI in paratype-a), about 1220 µm long, 40–85 µm wide, tubular and rather homogeneous throughout, with thin outer muscular layer. Prostate glands (Fig. 1 D, pr) small, attached to ental portion of atrium by short stalk. Soft part of penis (Fig. 1 D, pe) cylindrical, about 75 µm long, 65 µm in diameter, enclosed in copulatory sac; penis surrounded by thin cuticularized, somewhat thimble-shaped sheath (Fig. 1 H, ps; Fig. 1 I), 80 µm long, 68 µm wide, with 5 µm thick walls. Copulatory sac (Fig. 1 H, cs) 95 µm long, 80–100 µm wide, with outer muscular layer 10–20 µm thick.
Spermathecae (Fig. 2 A) paired in X–XIII (IX–XI in paratype-a). Ampulla (Fig. 2 A, sa) up to 600 µm long, maximally 390 µm wide. Duct (Fig. 2 A, sd) totally about 950 µm long, tripartite, consisting of: (1) ectalmost part, about 475 µm long, 50–75 µm wide, (2) pear-shaped vestibule (Fig. 2 A, sv), about 250 µm long, maximally 120 µm wide, (3) entalmost part, 200 µm long, 63–112 µm wide. Spermatozeugmata (Fig. 2 A, sz) about 500–900 µm long, 5–10 of them in ampulla, 1–2 in vestibule.
Distribution and habitat: Known only from Fuxian Lake, Yunnan Province, China. Freshwater lake, 97–113 m depth, water temperature lower than 14 ºC, fine clay.
Remarks: Judging from the long vasa deferentia, long tubular atria each with a small prostate gland, penes with distinct cuticular sheaths, and the atria longer than vasa deferentia, the new species fits the definition of Varichaetadrilus Brinkhurst, 1981. Nine species were previously known in the genus, all distributed in the Holarctic region (Timm, 2006).
Among the known members of Varichaetadrilus, there are two species with spermathecal vestibules: V. pacificus (Brinkhurst, 1981), originally known from Washington, USA (Brinkhurst, 1981), and V. fulleri Brinkhurst & Kathman, 1983 recorded only from Kentucky, USA (Brinkhurst & Kathman, 1983). However, V. vestibulatus n. sp. is easily separated from those two species by the modified spermathecal chaetae and the shape of penial sheaths (Table 2). In addition, the spermathecal duct of the new species has pear-shaped middle vestibule, but V. p a c i f i c u s has cervix-like ental vestibule, and V. f u l l e r i has ectal vestibule.
This is the first species of Varichaetadrilus recorded from China, and it is the lowest-latitude distributed member hitherto known in the genus.
TABLE 2. Comparison of Varichaetadrilus vestibulatus n. sp. and allied species.
description: Published as part of Cui, Yongde & Wang, Hongzhu, 2009, Three new species of Tubificinae, Oligochaeta, from two plateau lakes in Southwest China, pp. 45-54 in Zootaxa 2143 on pages 47-49, DOI: 10.5281/zenodo.188610