The genus Wieseria was established by Gerlach (1956). It is characterized by having setiform inner and outer labial sensilla; four cephalic setae; buccal cavity minute or absent; amphidial fovea in various shapes mainly with double contour, situated at the same level of or posterior to cephalic setae; a precloacal supplementary seta present; and conico-cylindrical tail with a swollen, pointed or bifurcate tip (Smol et al., 2014; Yu and Xu, 2017). To date, ten nominal species have been described under Wieseria (Yu and Xu, 2017; Campinas Bezerra et al., 2017). However, four species which described from females only were deemed to invalid species (Campinas Bezerra et al., 2017), and they are: Wieseria inaequalis Gerlach, 1956; W. longicaudata Timm, 1961; W. longiseta (Allgén, 1947) and W. pica Gerlach, 1956. Six species may be accepted as valid for the genus.

During an investigation of the biodiversity of free-living nematodes in the Jiaozhou Bay in 2016, two unrecorded species of Wieseria Gerlach, 1956 were found from subtidal sediment and are described as Wieseria sinica sp. nov. and Wieseria tenuisa sp. nov., respectively.

In July 2016, undisturbed sediments were obtained using a 0.1 m² Gray-O’Hara box from a grid of sampling stations in the Jiaozhou Bay. The separate sampling was performed using a sawn-off syringe with a 2.6 cm inner diameter. In a Gray-O’Hara box, the syringe was pushed into the sediment down to 8 cm depth and samples were divided into 0–2 cm and 2–8 cm fractions, and then fixed with equivalent 10% formalin in seawater for long term preservation. In the laboratory, samples were stained with 0.1% rose Bengal for 24 h (Higgins and Thiel, 1988). The stained samples were washed with tap water to remove residual formalin and then sieved over two mesh sizes (500 and 42 µm) to separate macrofauna (500 µm) from meiofauna (42 µm). Heavier sediment particles were removed using centrifugation in Ludox^TM (50% colloidal silica, suspension in water; product of Sigma Aldrich Co., USA) with a specific gravity adjusted to 1.15 g/mL (Jonge and Bouwman, 1977). Nematodes were transferred into 10 mL of a 9׃1 (v/v) solution of 50% ethanol ׃ pure glycerin in a cavity block. After ethanol and water were slowly evaporated, the specimens were mounted in glycerin on permanent slides (McIntyre and Warwick, 1984). The descriptions were made from glycerin mounts using a differential interference contrast microscope (Olympus BX53). Line drawings were made with the aid of a camera lucida. All measurements are given using Olympus software of cellSens Standard 1.12, and all curved structures were measured along the arc. Type specimens have been deposited in the Marine Biological Museum of Chinese Academy of Sciences, Qingdao, China.

Class Adenophorea Chitwood, 1950

Order Enoplida Filipjev, 1929

Family Oxystominidae Chitwood, 1935

Genus Wieseria Gerlach, 1956

Recently, Yu and Xu (2017) reviewed the genus Wieseria and separated ten species into three main groups, based mainly on the shape of tail tip. Group I is characterized by tail with a swollen tip; Group II is characterized by tail with a pointed tip; and Group III is characterized by tail with a bifurcate tip. Both Wieseria sinica sp. nov. and Wieseria tenuisa sp. nov. belong to Group I with a swollen tail tip. Wieseria sinica sp. nov. is characterized by having short labial and cephalic setae in a backward direction; oblong amphidial fovea with double contour; arcuate spicules with alea; ring-like guberculum; and clavated tail 7.3 a.b.d. long. It differs from the most similar species W. minor Yu and Xu, 2017 by its much longer body (2 398 µm vs. 1 045 µm) and the presence of spicules alae (vs. absent). Moreover, it differs from W. glandulosa (Kreis, 1929) Gerlach, 1956 by the presence of four cephalic setae (vs. absent); and from W. clavata Gerlach, 1956 by the position of cephalic setae (anterior to amphids vs. at the central level of the amphidial fovea) and the length of amphidial fovea (6 µm vs. 14 µm). Wieseria sinica sp. nov. differs from W. tenuisa sp. nov. by its larger body size (2 398 µm vs. 1 870 µm long); shorter outer labial setae (4 µm, in a backward direction vs. 7 µm, in a forward direction); arcuate spicules without hooked proximal end (vs. with hooked proximal end); and ring-like gubernaculum (vs. rodlike gubernaculum).

Wieseria tenuisa sp. nov. can be identified by its relatively long labial setae; oblong amphidial fovea with double contour; and spicules with hooked proximal end and alae. It differs from the similar species W. minor Yu and Xu, 2017 by its longer labial setae (7 µm vs. 3 µm), the presence of spicules alea (vs. absence), rodlike gubernaculums (vs. cuneate), much thinner body (a=133.6 vs. a=80.4), and longer tail (7.9 a.b.d. vs. 5.7 a.b.d.).

Amended dichotomous key to males of species of Wieseria (based on Smol et al. (2014); Yu and Xu (2017)):

1. Tail tip swollen or clavate……………………………....………………2

– Tail tip pointed or bifurcate…………………………………..6

2. Cephalic setae absent………………………………...……………… ………..…….......………W. glandulosa (Kreis, 1929) Gerlach, 1956

– Cephalic setae present…………………......……………………3

3. Cephalic setae at the central level of amphids………......……… …………………………………………….…W. clavata Gerlach, 1956

– Cephalic setae anterior to amphids…………….......…………………4

4. Spicules without ventral alae………W. minor Yu and Xu, 2017

– Spicules with ventral alae……………………………………………5

5. Labial setae longer than 2 h.d., spicule with hooked proximal end………………………..………..………………W. tenuisa sp. nov.

– Labial setae shorter than 2 h.d., spicule proximal end not hooked………...…...……………..…………………W. sinica sp. nov.

6. Tail tip pointed, body length < 1 mm…W. Leptura Vitiello, 1972

– Tail tip bifurcate…………..……………………………………………7

7. Gubernaculum present………W. scotlandica Zhang, 1983

– Gubernaculum absent………..…………W. hispida Vitiello, 1972

The authors are very grateful to Wang Chunming for his kind help in collecting samples and to Gao Qun for her slide making.