Potamothrix praeprostatus, Cui, Yongde & Wang, Hongzhu, 2012

Cui, Yongde & Wang, Hongzhu, 2012, Three new species of Potamothrix (Oligochaeta, Naididae, Tubificinae) from Fuxian Lake, the deepest lake of Yunnan Province, Southwest China, ZooKeys 175, pp. 1-17 : 3-4

Potamothrix praeprostatus sp. n.

Holotype.

IHB YAN 20021205b, mature specimen mounted in Canada balsam, and stained with borax carmine.

Type locality.

East of Lichang (24°32'04"N, 102°51'43"E) in Fuxian Lake, eastern Yunnan, China; depth 113 m, bottom temperature 13.5°C, dissolved oxygen at bottom 5.2 mg/L, total nitrogen in water 0.164 mg/L, total phosphorus in water 0.037 mg/L, fine clay; Dec 11, 2002, coll. Y. Cui and X. Liu.

Etymology.

“prae” and “prostatus” are Latin for “proximal” and “prostate”, respectively. The specific name refers to the prostate glands proximally attached to atria.

Description.

One complete specimen 7.6 mm long, diameter at XI about 0.8 mm, 27 segments. Prostomium conical. Clitellum inconspicuous.

Dorsal chaetae (Fig. 1 C–D) of II–IV bifid only, 7-10 per bundle, 135-148 µm long, 3.0-3.5 µm thick, upper tooth longer and thinner than lower, lower tooth occasionally bifurcated. Dorsal bundles of V–X with 5-8 hair chaetae and 5-7 bifid chaetae; plumose hair chaetae (Fig. 1A), 240-420 µm long, 2.6-3.2 µm thick basally; pectinate bifid chaetae (Fig. 1B), 120-140 µm long, 2.8-3.2 µm thick, with 1-2 intermediate teeth, upper tooth slightly longer and thinner than lower tooth (usually bifurcated), or equally long. Dorsal bundles in posterior segments with 1-4 hair chaetae and 2-6 bifid chaetae, shorter and thinner than those of anterior segments, hair chaetae 280-320 µm long, bifid chaetae 90-110 µm long, 2.6-2.8 µm thick. Ventral chaetae (Fig. 1 D–E) bifid, 6-8 per bundle anteriorly, 140-150 µm long, 3.0-3.5 µm thick; 2-4 (5) per bundle in postclitellar segments, 80-110 µm long, 2.4-3.2 µm thick, all with teeth similar to the ones in dorsal chaetae in II-IV. Spermathecal chaetae (Fig. 1F, H, sc) one per bundle in middle to posterior of X, entally embedded in glandular sacs, about 145-160 µm long, 4.0 µm thick, with ectal part grooved. Penial chaetae absent. Male pores paired in line with ventral chaetae, anterior to middle of XI. Spermathecal pores paired in line with ventral chaetae, posterior to middle of X, immediately anterior to spermathecal chaetae.

Pharyngeal glands in II–III. Chloragogen cells from VI onwards. No coelomocytes. Male genitalia (Fig. 1G) paired. Vasa deferentia (Fig. 1G, vd) 38-65 µm long, 16-22 µm wide, entering atria apically. Atria (Fig. 1G, at) 690 µm long, 28-80 µm wide, tubular and rather homogenous throughout, with thin outer muscular layer and thick inner epithelium. Prostate glands (Fig. 1G, pr) small, proximally attached to atria, and far from vasa deferentia. Soft part of penis (Fig. 1G, pe) small, 38-54 µm long, 22-44 µm wide, cylindrical, enclosed in penial sacs. Penial sacs (Fig. 1G, ps) 65-80 µm long, 54-80 µm wide, with muscular layer 3-4 µm thick.

Spermathecae (Fig. 1H) in X–XII, ducts (Fig. 1H, sd) 470-490 µm long, 38-65 µm wide, ampullae (Fig. 1H, sa) elongated, 520-540 µm long, maximally 300-315 µm wide. Spermatozeugmata (Fig. 1H, sz) 5-8 in each ampulla, about 300-460 µm long.

Distribution and habitat.

Known only from its type locality, Yunnan Province, China; freshwater lake, 113 m depth, water temperature less than 14 °C, fine clay.

Remarks.

According to short vasa deferentia, long tubular atria, each with a small prostate gland, and lack of ejaculatory ducts, the new species fits more closely the definition of Potamothrix Vejdovský & Mrázek, 1902 than that of any other described tubificine genus ( Brinkhurst and Jamieson 1971; Finogenova and Poddubnaja 1990).

Potamothrix praeprostatus sp. n. differs from its allies by its prostate glands joining atria in their proximal to middle portion. With regard homogenous atria with prostate glands, the new species is similar to Potamothrix postojnae Karaman, 1974, Potamothrix scleropenis Cui & Wang, 2005, Potamothrix aductus Cui & Wang, 2012, and Potamothrix paramoldaviensis sp. n. However, these species differ from Potamothrix praeprostatus sp. n. in that Potamothrix postojnae has no spermathecal chaeta ( Brinkhurst and Wetzel 1984); Potamothrix scleropenis has penial sheath ( Cui and Wang 2005); Potamothrix paramoldaviensis sp. n. has no hairs and no penis (Fig. 2); Potamothrix aductus Cui & Wang, 2012 has no spermathecal duct and its spermathecal chaeta has contorted ectal part.