Rhyacodrilus tanggulaensis Jiang & Cui, 2023

Jiang, Wei, Zhou, Tingting, Wang, Hongzhu, Erséus, Christer & Cui, Yongde, 2023, Integrative taxonomy of a new species of Rhyacodrilus (Annelida: Clitellata: Rhyacodrilinae) from Tibet Plateau rivers, with a preliminary assessment of its phylogenetic position, Zootaxa 5256 (2), pp. 125-138 : 130-131

publication ID	https://doi.org/ 10.11646/zootaxa.5256.2.2
DOI	https://doi.org/10.5281/zenodo.7746359
persistent identifier	https://treatment.plazi.org/id/03BB87C1-FFE7-451E-FF3C-FAC768CCFC31
treatment provided by	Plazi
scientific name	Rhyacodrilus tanggulaensis Jiang & Cui
status	sp. nov.

Treatment

Rhyacodrilus tanggulaensis Jiang & Cui , sp. nov.

Holotype. IHB TTH20170720 a, mature specimen, stained and whole-mounted in Canada balsam.

Type locality. Tongtian River (34.1084 N, 95.7199 E), Yushu City , Qinghai province, China. Elevation 4077 m a.s.l, water temperature 15.3 °C, pH 8.3, dissolved oxygen 7.1 mg. l-1, conductivity 801 μS/cm. Collected by Yongde Cui and Tingting Zhou on 20 July 2017 GoogleMaps .

Paratypes. IHB XZ20200903 About IHB b, 1 mature specimen whole-mounted in Canada balsam, Nagqu river in Tibet (31.6574 N, 92.0219 E). Elevation 4586 m a.s.l., water temperature 12.3 °C, pH 8.7, dissolved oxygen 6.1 mg. l-1, and conductivity 485 μS/cm. Collected by Yongde Cui , Tingting Zhou and Wei Jiang on 09 September 2020 GoogleMaps .

Other material. 3 specimens from the Nagqu River for scanning electron microscopy. The species was also observed, but not studied in detail, in Za’gya Zangbo River.

Etymology. Named tanggulaensis after the Tanggula Mountains. The rivers where the specimens were collected are all related to the Tanggula Mountains.

Description. Length about 8–9 mm, width at genital segments X–XI about 0.5–0.6 mm. Segments 35–45. Prostomium round. Coelomocytes large, abundant, granulated, diameter 8–16μm. Clitellum extending over 1/2X–XI.

Dorsal and ventral bundles with 4–5 bifid chaetae, 75–90 μm long, 2–3 μm wide, distal tooth 2–3 times longer than proximal ( Figs. 1A View FIGURE 1 , 2A, B View FIGURE 2 ). Hair chaetae absent. Modified spermathecal chaetae in segment X ( Figs. 1B View FIGURE 1 , 2D View FIGURE 2 ), 1–2 per bundle, 75–100 μm long, 4–5 μm wide, bifid with very long, sharply-pointed distal tooth and rounded proximal end. The same kind of chaetae present in IX and XII. Penial chaetae in XI, 4 per bundle, 75–100 μm long, 4–5 μm wide, single-pointed with slightly curved tips ( Fig. 2C View FIGURE 2 ). Male pores paired, close to the mid-ventral line of the body, immediately anterior to penial chaetae in XI. Spermathecal pores paired, in line with ventral chaetae, immediately anterior to spermathecal chaetae in X.

Male genitalia paired in X–XI ( Fig. 1C View FIGURE 1 ). Sperm funnel cup-shaped. Vas deferens 1–1.5 mm long, 13–15 μm wide, joining the atrial ampulla subapically. Atrium elongated, 0.7–1 mm long, 70–82 μm wide, roughly tubular, covered by a continuous thick layer of prostatic cells. Atrial duct 300–400 μm long, 25–30 μm wide, with a tortuous lumen. Spermathecae 250–300 μm long, 100–110 μm wide, with short ducts; large masses of randomly arranged sperm in lumina.

Distribution and habitat. Known only from Qinghai-Tibet Plateau, in rivers> 4000m above sea level. Some rivers are at the foot of snow mountain ( Fig. 3 View FIGURE 3 ). The sampling area is surrounded by natural plateau grassland. The collection site is a shallow permanent stream with gravel and cobbles sediment.

Remarks. Genus level. Morphologically, the new species belongs to the genus Rhyacodrilus based on the presence of spermathecal and penial chaetae, the rich occurrence of coelomocytes, the vas deferens being longer than the atrium and joining it subapically, and the continuous coverage of the atrium with a layer of prostate cells (Brinkhurst & Jamison 1971).

Species level. In Rhyacodrilus there are currently 11 species which possess both spermathecal and penial chaetae; they are listed in Rodríguez & Fend (2013, Table 1 View TABLE 1 ). Among them, three species are devoid of hair chaetae, R. carsticus Košel, 1980 , R. gernikensis Giani & Rodriguez, 1988 , and R. ardierae Lafont & Juget, 1993 . A comparison of these species with Rhyacodrilus tanggulaensis sp. nov. is given in Table 3 View TABLE 3 . Some obvious differences are as follows: R. carsticus and R. ardierae have globular to oval atria (elongate-tubular in the new species), and R. gernikensis has unmodified genital chaetae and a pear-shaped atrium (see Giani & Rodríguez 1988; Rodríguez & Fend 2013, Achurra & Rodríguez 2016).

Geographical distribution. R. ardierae , R. carsticus and R. gernikensis are only known from groundwater habitats at a few sites in western to central Europe ( Achurra & Rodriguez 2016). The new species described here is only distributed in rivers above 4000 m elevation on the Qinghai-Tibet Plateau. In this area the river sediments are mainly composed of clean sand and gravel. It is worth noting that the highest distribution is 5263 m above sea level, a locality near Tanggula Mountain, the source of Za’gya Zangbo, Tibet's largest inland river.