Potamothrix moldaviensis Vejdovský and Mrázek, 1902

Hair chaetae present or absent, dorsal chaetae bifid and always pectinated, or only bifids. Ventral chaetae bifids. No coelomocytes. Vas deferens very short, entering atrium apically; atrium tubular, long. Prostate gland small, attached to proximal part of atrium by a short stalk, or no prostate gland. No ejaculatory duct. Penis with or without cuticular sheath. Spermatozeugmata present. Modified spermathecal chaetae present or absent.

The genus Potamothrix, established by Vejdovský and Mrázek (1902) for Potamothrix moldaviensis Vejdovský & Mrázek, 1902, was revised by Holmquist (1985) and Finogenova and Poddubnaja (1990). Altogether, 20 species were previously known and mainly distributed in the Holarctic region (Table 1) (Brinkhurst and Jamieson 1971; Hrabě 1981; Brinkhurst and Wetzel 1984; Finogenova and Poddubnaja 1990; Šporka 1994; Milbrink 1999; Milbrink and Timm 2001). Through recent investigation of the plateau lakes, three species of Potamothrix (Oligochaeta: Tubificinae), Potamothrix rhytipeniatus Cui & Wang, 2012, Potamothrix aductus Cui & Wang, 2012 and Potamothrix scleropenis, have been found in the Fuxian Lake and Xingyun Lake of Yunnan Province, Southwest China (Cui and Wang 2005). They are the lowest-latitude members of the genus hitherto known. Moreover, studies show that Potamothrix is unexpectedly species-rich in plateau lakes of Yunnan Province, especially in Fuxian Lake where five species were recorded (Cui 2008; Cui and Wang 2005; Cui et al. 2008). In this paper, we will give the description of three new species, Potamothrix praeprostatus sp. n., Potamothrix paramoldaviensis sp. n. and Potamothrix parabedoti sp. n., from Fuxian Lake.

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

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.

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

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

Dorsal chaetae (Fig. 1C–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. 1D–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.

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

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 thatPotamothrix 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.

IHB YAN 20020812i, mature specimen mounted in Canada balsam, and stained with borax carmine.

East of Gushan Island (24°24'05"N, 102°52'45"E) in Fuxian Lake, eastern Yunnan, China; depth 78 m, bottom temperature 15.9 °C, dissolved oxygen at bottom 9.6 mg/L, total nitrogen in water 0.155 mg/L, total phosphorus in water 0.0234 mg/L, fine clay; Aug 8, 2002, coll. Y. Cui and X. Liu.

Named “paramoldaviensis” for its resemblance with Potamothrix moldaviensis Vejdovský & Mrázek, 1902 in terms of its male genitalia.

Specimen incomplete, length > 4.4 mm, diameter at XI about 0.7 mm, segments > 13. Clitellum inconspicuous.

Chaetae (Fig. 2A–B) all bifid, 4–6 per bundle dorsally, 3–6 per bundle ventrally, 80–120 µm long, 2.0–2.6 µm thick, upper tooth longer and thinner than lower. Spermathecal chaetae (Fig. 2D) one per bundle in posterior to middle of X, entally embedded in glandular sacs, 145–160 µm long, 4.0–4.5 µm thick, with curved ental part, and grooved ectal part. Penial chaetae (Fig. 2C, F, pc) slightly different to other ventral chaetae, 1–2 per bundle in postero-XI, 70–74 µm long, 2.0–2.4 µm thick, upper tooth as long as, but thicker than lower tooth. Male pores paired in line with ventral chaetae in postero-XI, immediately anterior to penial chaetae. Spermathecal pores paired in line with ventral chaetae in 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. 2F) paired. Vasa deferentia (Fig. 2F, vd) very short, 27–38 µm long, 16–20 µm wide, entering atria apically. Atria (Fig. 2F, at) 1050–1130 µm long, 38–90 µm wide, tubular and rather homogenous throughout, with thin outer muscular layer and thick inner epithelium. Prostate gland small, attached proximally to atrium. Penis absent.

Spermathecae ducts (Fig. 2E, sd) 345–360 µm long, 38–70 µm wide, ampullae (Fig. 2H, sa) pear-shaped, 420–430 µm long, maximally 230–250 µm wide. Spermatozeugmata (Fig. 2H, sz) 6–9 in each ampulla, about 300–640 µm long.

Known only from its type locality, Yunnan Province, China; freshwater lake, 78 m depth, water temperature less than 16 °C, fine clay.

According to very 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).

This new speciesresembles Potamothrix moldaviensisin some aspects of the male organs (Vejdovský and Mrázek 1902), e.g. the very short vasa deferentia, tubular atria, and the length ration of the vasa diferentia to the atria, and their differences are obvious. Potamothrix paramoldaviensis sp. n. has homogenous atria with prostate glands and no penes, while Potamothrix moldaviensis has tripartite atria without prostate glands, with short penes.

The new species is distinguishable from other species from the Yunnan lakes in the characteristics of some somatic chaetae. For instance, hair chaetae and pectinate bifid chaetae are present in Potamothrix scleropenis Cui & Wang, 2005, Potamothrix rhytipeniatus Cui & Wang, 2012, Potamothrix aductus Cui & Wang, 2012, Potamothrix praeprostatus sp. n. and Potamothrix parabedoti sp. n., but hair chaetae are absent in Potamothrix paramoldaviensis; the spermathecal chaetae of these six species are dissimilar; slightly modified penial chaetae are present in Potamothrix scleropenis and Potamothrix paramoldaviensis, but are absent in the other three species (Table 2).

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

IHB YAN20021205c, 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.

IHB YAN20021012b, East of Gushan Island (24°24'05"N, 102°52'45"E) in Fuxian Lake, eastern Yunnan, China; depth 76 m, bottom temperature 14.8 °C, dissolved oxygen at bottom 8.7 mg/L, total nitrogen in water 0.163 mg/L, total phosphorus in water 0.0203 mg/L, fine clay; Oct 8, 2002, coll. Y. Cui and X. Liu. IHB YAN20021009c, North of Dasazui (24°22'58"N, 102°49'49"E) in Fuxian lake, eastern Yunnan, China; depth 87 m, bottom temperature 14.7 °C, dissolved oxygen at bottom 8.7 mg/L, total nitrogen in water 0.165 mg/L, total phosphorus in water 0.022 mg/L, fine clay; Oct 8, 2002, coll. Y. Cui and X. Liu.

Named “parabedoti” for its resemblance with Potamothrix bedoti (Piguet, 1913) in terms of male genitalia.

Two complete specimen 8.9–19.8 mm long (Holotype: 8.9 mm), with 36–131 segments (Holotype: 36), diameter at XI about 0.8 mm. Prostomium conical. Clitellum inconspicuous.

Dorsal chaetae (Fig. 3B) of II (II–IV) bifid only, 7–8 per bundle, 100–145 µm long, 2.8–3.0 µm thick, upper tooth longer and thicker than lower. Dorsal bundle of III (V)-IX 4–8 hair chaetae and 5–8 bifid chaetae per bundle; plumose hair chaetae (Fig. 3A), 250–300 µm long, 2.8–3.2 µm thick basally; pectinate bifid chaetae (Fig. 3C–D), 140–150 µm long, 2.8–3.2 µm thick, with 1–3 intermediate teeth, upper tooth slightly longer and thinner than lower (usually bifurcated), or equally long. Dorsal bundles of posterior segments 2–4 hair chaetae and 3–4 bifid chaetae per bundle, shorter and thinner than those of anterior segments, hair chaetae 200–240 µm long, bifid chaetae 100–120 µm long, 2.6–2.8 µm thick. Ventral chaetae (Fig. 3E–F) bifid, 6–10 per bundle anteriorly, 100–150 µm long, 2.8–3.0 µm thick; 3–5 per bundle in postclitellar segments, 100–125 µm long, 2.4–2.6 µm thick, all with tooth similar to dorsal chaetae in II–IV. Spermathecal chaetae (Fig. 3I) one per bundle in middle to posterior of VIII or IX, entally embedded in glandular sacs, about 125–140 µm long, 4.0 µm thick, ental end strongly curved, with ectal part grooved. Penial chaetae absent. Male pores paired in line with ventral chaetae, middle to posterior of IX or X. Spermathecal pores paired in line with ventral chaetae, middle of X, immediately anterior to spermathecal chaetae.

Pharyngeal glands in II. Chloragogen cells from IV or V onwards. No coelomocytes. Male genitalia (Fig. 3G) paired. Vasa deferentia (Fig. 3G, vd) 45–70 µm long, 18–24 µm wide, entering atria apically. Atria (Fig. 3G, at) 880 µm long, 44–80 µm wide, tubular and rather homogenous throughout, with thin outer muscular layer and thick inner epithelium. Prostate gland absent. Soft part of penis (Fig. 3G, pe) cylindrical and tapering ectally, 80–100 µm long, basally 45–60 wide, ectally 25–36 wide, enclosed in penial sacs. Penial sac (Fig. 3G, ps) 80–130 µm long, 72–92 µm wide, with muscular layer 2–4 µm thick.

Spermathecae (Fig. 3H) in VIII–XIII or VIII, ducts (Fig. 3H, sd) 500–568 µm long, 74–95 µm wide, ampullae (Fig. 3H, sa) elongated, 470–1280 µm long, maximally 320–442 µm wide. Spermatozeugmata (Fig. 3H, sz) 10–25 in each ampulla, about 400–860 µm long.

Known only from its type locality, Yunnan Province, China; freshwater lake, 70–110 m depth, water temperature less than 15 °C, fine clay.

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

The new speciesresembles Potamothrix bedoti (Piguet, 1913)in some aspects of reproductive organ (Vejdovský and Mrázek 1902), e.g. has a very short vasa deferentia, tubular atria without prostate gland, the length ration of vasa diferentia to atria, and the reproductive organs move to VIII–X. However, their differences are obvious. Potamothrix parabedoti sp. n., has homogenous atria with prostate glands, while Potamothrix bedoti has tripartite atria without prostate glands. In additional, the shapes of spermathecal chaetae are dissimilar in two of the species, the form is scalpel-like, and the ental part straight in Potamothrix bedoti (Timm 1970, 1999), but the ental end part is strongly curved in Potamothrix parabedoti sp. n (Fig. 3I).

The new species are distinguishable from other species from Yunnan Lakes in that of the position of their reproductive organs and the characteristic of some somatic chaetae. For instance, the reproductive organs are move to VIII–X in Potamothrix parabedoti sp. n. but that were in X–XIII in other species; the hair and pectinate bifids are absent in Potamothrix rhytipeniatus and Potamothrix paramoldaviensis sp. n., but present in other four species.