Potamothrix paramoldaviensis, 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 : 4-6

Potamothrix paramoldaviensis sp. n.

Holotype.

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

Type locality.

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.

Etymology.

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

Description.

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

Chaetae (Fig. 2 A–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.

Distribution and habitat.

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

Remarks.

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).