Pilatobius cf. rugosus (Bartoš, 1935)

Hypsibius (Diphascon) rugosus; locus typicus: Karlik near Mošovce, Slovakia; Bartoš (1935).

D. rugosus; Tatra Mountains, Poland; Dastych (1980).

D. rugosum; various locales, Poland; Dastych (1988).

Material examined: 40 individuals in total (for details, see Supporting Information, Table S1).

Description: Body small to medium in size (Table 13), corpulent (Fig. 38A) and white. Cuticle uniformly sculptured on the entire dorsal surface by polygons of various sizes placed tightly adjacent to each other (Fig. 38B, C); legs smooth. Cribriform areas not visible under PCM. Legs short, plump, and barely delimited from the trunk (Fig. 38A). Eyes present in living animals, but usually quickly dissolving in Hoyer’s medium. Buccopharyngeal apparatus of the Pilatobius type, with a short pharyngeal tube (Fig. 38D). The OCA not visible under PCM (Fig. 38D). Furcae of the Hypsibius type. The DABT large and slightly elongate. Pharynx circular, with large pharyngeal apophyses. Macroplacoid length sequence 2 <1, the first with a delicate central constriction (Fig. 38D). Septulum large, but clearly shorter than the second macroplacoid.

Claws of the Hypsibius type, with external and internal claws of similar size (Fig. 39). Accessory points slightly divergent. All claw bases distinctly narrowed, but especially the anterior claws, which have calyx-like bases (Fig. 39B, D). Pseudolunulae absent. Cuticular bars present and of three types: (i) internal, long thickenings terminating at the claw I–III bases (Fig. 39A); (ii) anterior and (iii) posterior short rods (Fig. 39B). All cuticular bars are undetectable in SEM (Fig. 39C, D).

Remarks: Currently, there are two discriminative traits separating P. rugosus and P. iltisi (Schuster & Grigarick, 1965): the presence of deep transverse cuticular folds in P. iltisi and, according to Bartoš (1935) and Schuster and Grigarick (1965), the diameter of the polygonal granules that constitute the sculpturing increasing posteriorly in P. rugosus but not in P. iltisi . These cuticular folds could be a result of the preparation technique [see ‘Remarks’ on P. sexbullatus (Ito, 1995)]. The dorsal sculpturing in our examined population does not agree with the original description but conforms to specimens identified as P. rugosus by Dastych (1988), thus indicating that resampling in the Turiec Basin is needed to verify the true morphotype of P. rugosus . General claw morphology is similar in P. rugosus, P. recamieri (Richters, 1911) (see Gąsiorek et al. 2017), and P. secchii (Bertolani & Rebecchi, 1996) nom. inq. (Fig. 42E). Sculpture of P. ramazzottii (Robotti, 1970) is similar to that of P. rugosus; however, the polygons are larger and closer to each other (Fig. 42F). Within the rugosus group (species with the entire dorsum covered by sculpturing and lacking dorsal gibbosities), four other species are gathered: P. granifer (Greven, 1972), P. latipes (Mihelčič, 1955) sp. dub., P. procerus (Pilato et al., 2014), and P. ziliense (Lisi et al., 2014) . Of these, Dastych (2015) has already expressed doubts regarding the validity of P. latipes, with which we concur. P. granifer differs from P. rugosus by a completely dissimilar type of sculpturing [irregular small polygons in P. rugosus vs. large polygons resembling the caudal sculpturing of some species of the Ramazzottius oberhaeuseri (Doyère, 1840) complex, but clearly larger and with a conspicuous light centre in P. granifer; see Fig. 42G]. Unfortunately, other differences cannot be given, because the description of P. granifer is insufficient, and the type material lost (H. Greven, pers. comm.). In our opinion, both P. procerus and P. ziliense are poorly differentiated from P. rugosus and require further investigation. P. nodulosus is distinguished from P. rugosus by its dissimilar type of sculpturing: very large polygons in the caudal zone (Fig. 42D), with the size of the polygons subsequently decreasing anteriorly. The internal and anterior claws of the former species are also more massive (Fig. 42C, D), rectangular bars are present below claws (Fig. 42C, D), and claws IV have evident pseudolunulae (Fig. 42D).