Pseudechiniscus xiai Wang & Xue & Li 2018, sp. nov.

Pseudechiniscus xiai sp. nov.

(Table 1, Figs. 1–5)

Material examined: Specimens extracted from mosses growing on rocks. Holotype: Female, slide wqc01023. Paratypes: 7 females (slides wqc01022, wqc01024, wqc01025, wqc01026, wqc01030, wqc01034, wqc03010) and a male (slide wqc01027).

Type locality: wqc01022–wqc01027, wqc01030–wqc01034, 34.75076N, 106. 22221E, 1426m asl, moss growing on rocks; wqc03010, 34.75048N, 106.22158E, 1483m asl, moss growing on rocks. Miss Jing Xue and Panpan Xian collected the moss samples in early summer of 2016.

Type repository: Xiaochen Li’s tardigrade collection, Molecular Ecology Laboratory, Department of Biology, College of Life Sciences of Shaanxi Normal University, China.

Description of holotype: Small body size, body length 198µm (Table 1). Body colour orange. Eyespots black, granular, solid. Cuticular sculpture consists of dots, striae between dots not visible under Light Microscopy. Dots in central part of the plates larger than those near margin (Fig. 1c, e). The diameter of the largest dot is about 1µm. Stylet supports present, pharyngeal tube present, pharyngeal bulb roundish, placoid present. Rostral end of head plate facetted (Fig. 1a). Cephalic papillae (secondary clavae) dome-shaped, primary clavae water drop-shaped (Fig. 2b, d). Cuticular plates with very marked margins. Three undivided median plates present, paired segmental plates without smooth band, pseudosegmental plate unpaired with a smooth caudal margin. Terminal plate without notches, not facetted. Lateral intersegmental platelets present on lateral side of all median plates, two on each side of each median plate, 12 in total. Ventral cuticular granulation present with a dense patch between legs I, II and III. Ventral dots arranged in a reticular patched design (Fig. 1).

Dots present on basal part of legs, dots on legs much smaller than dots on dorsal plates. Spine on all legs absent, papillae present on leg 4 (Fig. 1d). Dentate collar absent on leg 4, small spur present on internal claws of all legs, spurs located near the base of claws, and pointed downward (Fig. 1f).

Eggs. unknown.

For detailed measurements of the holotype and ranges of the paratypes see Table 1 and Supplementary Materials.

Etymology: This species is dedicated to Prof. Haibin Xia, Dean of College of Life Sciences of Shaanxi Normal University, for his contributions to the development of our college.

Differential diagnosis: The genus Pseudechiniscus was divided into two groups: the victor group with trunk cirri or spines B, C, D and E, the suillus / conifer group without trunk cirri or spines B, C, D and E (Kristensen 1987). This genus has since been revised and the victor group was moved into a new genus, Acanthechiniscus (Vecchi et al. 2016). The revised Pseudechiniscus genus contains 39 species/subspecies (Degma et al. 2007, 2017). Lateral appendices (filaments, spines or papillae) except cirri A and projections (lobes, spines, teeth or triangular projections) on posterior margin of pseudosegmental plate are important characters for distinguishing species of the Pseudechiniscus. Lateral appendices and projections on posterior margin of pseudosegmental plate are absent in the following 10 species: Pseudechiniscus beasleyi Li et al., 2007, Pseudechiniscus chengi Xue et al., 2017, Pseudechiniscus clavatus Mihelčič, 1955, Pseudechiniscus dicrani Mihelčič, 1938, Pseudechiniscus facettalis Petersen, 1951, Pseudechiniscus jiroveci Bartoš, 1963, Pseudechiniscus juanitae de Barros, 1939, Pseudechiniscus megacephalus Mihelčič, 1951, Pseudechiniscus suillus (Ehrenberg, 1853) and Pseudechiniscus xiai sp. nov..

Pseudechiniscus xiai sp. nov. differs from:

Pseudechiniscus beasleyi by unpaired pseudosegmental plate and lacking notches on terminal plate (Li et al. 2007).

Pseudechiniscus chengi by unpaired pseudosegmental plate, lacking notches on the terminal plate, and median plate 3 always present (Xue et al. 2017).

Pseudechiniscus clavatus mainly by smaller and conical clava (Mihelčič 1955).

Pseudechiniscus dicrani mainly by curved posterior margin of pseudosegmental plate (Mihelčič 1938, Ramazzotti & Maucci 1983).

Pseudechiniscus facettalis by always having an unpaired pseudosegmental plate, and terminal plate unfacetted and without notches (Petersen 1951).

Pseudechiniscus jiroveci by unpaired pseudosegmental plate, lacking notches on the terminal plate and median plates 2 and 3 always present (Bartoš 1963).

Pseudechiniscus juanitae by lacking notches on terminal plate and by having spurs on the internal claws (de Barros 1939).

Pseudechiniscus megacephalus mainly by dome-shaped cephalic papilla instead of a mushroom-shaped papilla (Mihelčič 1951).

Pseudechiniscus suillus by lacking notches on terminal plate, having lateral intersegmental plates on the side of the median plates, unpaired pseudosegmental plate, and cuticular sculpture on ventral side of body in a reticular patched design (Ehrenberg 1853).