Potamothrix parabedoti, 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 : 7-8

Potamothrix parabedoti sp. n.

Holotype.

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

Type locality:

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.

Paratypes:

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.

Etymology:

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

Description:

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. 3 C–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. 3 E–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.

Distribution and habitat:

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

Remarks:

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 Cui & Wang, 2012 and Potamothrix paramoldaviensis sp. n., but present in other four species.