Two species of Naididae (Annelida, Clitellata) from southern Tibet, China

Abstract One new species of Naidinae (Oligochaeta, Naididae), Nais badia sp. n. and one new record species from China, Tubifex montanus Kowalewski, 1919 (Tubificinae) are found in southern Tibet. The new species is distinguished from congeners by its large area of reddish brown pigment in the anterior segments I–VIII, serrate hairs, pectinate needles with 1–2 intermediate teeth, ventral chaetae partly with 1–2 fine intermediate teeth and wave-like movements. The new material of the species Tubifex montanus differs slightly from the previous descriptions by its vas deferens entering atrium subapically, wide ental end of penial sheath and smooth hair chaetae.


Introduction
The Tibetan Plateau is one of the biodiversity hotspots around the globe for its unique natural environment (Li and Fang 1999), which accounts for the rich occurrence of endemic species of various taxa in this region, such as Triplophysa cakaensis (Cobitidae) (Cao and Zhu 1988), Schizothorax waltoni (Cyprinidae) (Chen and Chen 2010), and Alona aliensis (Chydoridae) (Chiang et al. 1983). What about oligochaetes? In the 20th century, there were only seven species of oligochaetes recorded in Tibet (Stephenson 1909;Černosvitov 1942;Liang 1963Liang , 1979Liang et al. 1998). Recently, He recorded 26 species in Tibet (He 2011;He et al. 2012), though focusing mainly on large rivers (Yarlung Zangbo River) and brackish lakes (Lake Nam Co and Lake Yamzho Yumco). Some freshwater wetlands among mountains in Tibet had been neglected, which we thought may be the ideal habitats for aquatic oligochaetes. In this paper, we describe one new species, Nais badia sp. n., and one new record of Tubifex montanus Kowalewski, 1919 found in a freshwater wetland of Cuomujiri Mountain, southern Tibet.
The samples were collected with a D-frame dip net, and cleaned through a 250 µm sieve. Large worms were sorted in a white porcelain dish manually and small individuals were sorted with a dissecting microscope. Specimens were all preserved in 10% formalin. Some specimens were investigated with a Scanning Election Microscopy (SEM) to reveal more details of the chaetae. Some were stained with borax carmine, dehydrated in a series of alcohol, cleared in xylene and mounted whole in Canada balsam for careful observation. Parameters of external morphology were established under glycerine mounts. Other parameters were studied on permanent mounts. Drawings were made with a camera lucida. All microscopic observations, including live observations, were documented photographically. The types and other specimens were all deposited in the Institute of Hydrobiology (IHB), Chinese Academy of Sciences (CAS), Wuhan, China.
Other material. 40 specimens are preserved in 10% formalin. 30 June 2013, collected from the type locality.
Etymology. The specific name "badia" is Latin for "badius", and refers to this worm's large area of reddish brown pigment in anterior segments I-VIII.
Remarks. The presence of eyes, dorsal chaetae beginning in VI consisting of hairs and double-pronged needles, pharynx in II-III, stomach beginning in VII, coelomocytes present, spermathecae with distinct ducts, male ducts paired in V-VI, vas deferens with prostate glands joining atrium subapically, atrium without prostate, penial chaetae present with a simple hook, indicate that this new species fits the definition of Nais Müller, 1773 (Sperber 1948;Brinkhurst and Jamieson 1971).
Nais badia sp. n. is distinguished from congeners for having a large area of reddish brown pigment in anterior segments I-VIII, hairs all serrate, needles pectinate with 1-2 intermediate teeth, ventral chaetae with (0)1-2 fine intermediate teeth (Only visible under SEM) and wave-like movements (Table 1). We are hence of the opinion that it can be described as new to science.
This new species is similar to Nais africana Brinkhurst, 1966 for having pectinate needles, but differs from it by its ventral chaetae in II-V differing from the rest, although the position of Nais africana in the genus is regarded as uncertain due to a lack of detailed examination of live worms and sectioned materials (Brinkhurst 1966). Nais elinguis resembles the new species on the needles and simple pointed penial chaetae, but its long and wide atrial duct, slow stomach dilatations and the vas deferens which is completely surrounded by abundant prostate gland cells are significantly different from the new species. With regard to the vas deferens completely surrounded by prostate gland cells on their posterior part, this new species is similar to Nais communis, Nais variabilis and Nais pardalis. However, some characteristic features of these species distinguish them from the new species. Nais communis eyes are generally absent, stomach dilatations are slow and the atrium is as long as the duct. Nais variabilis, Nais pardalis  1966Sperber 1948Brinkhurst and Jamieson 1971;Semernoy 2004 and Nais bretscheri all have the ventral chaetae in II-V that differ from the remaining segments. Nais pardalis the stomach has obvious elongated cells. Nais bretscheri the ventral chaetae have typical giant chaetae.
Remarks. According to the characteristics of a long vas deferens entering pearshaped atrium subapically, large compact prostate gland with stalk-like attachments   Hrabě 1939Hrabě , 1981Brinkhurst and Jamieson 1971 to atrium and penis with funnel-like penial sheath, the species fits the definition of Tubifex Lamarck, 1816 (Brinkhurst and Jamieson 1971).
The new material resembles Tubifex montanus Kowalewski, 1919 in absence of spermathecae, vas deferens nearly of a similar length with cilia throughout, pear-shaped atrium with quite long ejaculatory duct gradually becoming narrower toward the ectal end, large compact prostate gland empting into the atrial ampullae near the sperm duct outlet, cylindrical penis, surrounded by cuticularized and funnel-like penial sheath, and nearly the same type of dorsal ventral chaetae (Table 2).
However, the new material differs slightly from the description by Hrabě (1939Hrabě ( , 1981 by having the vas deferens entering the atrium subapically, straight penis sheath with ental end wider and smooth hair chaetae.