Pilatobius oculatus (Murray, 1906)

Diphascon oculatum; terra typica: Forth Valley, Scotland; Murray (1906b).

D. oculatum; Loch Ness, Scotland; Murray (1907).

Hypsibius oculatus; Warwickshire, England; Le Gros (1957).

H. (D.) oculatus; Brecon Beacons, England; Morgan and King (1976).

Material examined: 158 individuals in total (for details, see Supporting Information, Table S1).

Neotype material: Neotype and 15 specimens (slides GB.022.01– 04) from Scotland, Aberdeenshire, Bennachie, Oxen Craig (57°17 ʹ 36″N, 2°33 ʹ 37″W; 520 m a.s.l.), mixed soil and leaf litter from bedrock, 20 September 2015, Blagden coll., are deposited in the Institute of Zoology and Biomedical Research, Jagiellonian University, Kraków; 11 specimens (slide GB.022.05; NHMD Catalogue number 1651666) are deposited in the Natural History Museum, University of Copenhagen, Denmark.

Redescription: Body small to medium in size (Table 12), elongate and tapering anteriorly (Fig. 35A), white. Cuticle intensively wrinkled starting from the level of the first leg pair to the caudal zone, with the most intense transverse wrinkles at the level of the third leg pair (Fig. 35B). Cribriform areas (3–6) identifiable under PCM as large light ovals, particularly clearly visible in the wrinkled areas and in the sculptured caudal dorsum (Fig. 35C). Dorsum strongly sculptured in its posterior part (Fig. 35C); only rarely is this sculpture faint. Isolated sculptured areas are present on the dorsolateral cuticle up to the level of the second leg pair (Fig. 35B). Sculpture composed of numerous irregular polygons. Legs long, devoid of sculpturing or pedal gibbosities (Fig. 35A). Eyes always present in living animals, consisting of a few large granules merged into one eyespot (Fig. 36A). Long buccopharyngeal apparatus of the Pilatobius type (Fig. 36A, B). The OCA not visible under PCM (Fig. 36A). Furcae of the Hypsibius type. The DABT large and round, lying directly above the transition zone between the buccal and very thin pharyngeal tubes, the latter with annulation of the Pilatobius type (Fig. 36C). Annuli vanish ~2 μm before the pharyngeal apophyses (Fig. 36D), which are large (Fig. 36A, E). Pharynx circular (Fig. 36A). Macroplacoid length sequence 2 <1, both with constrictions detectable under PCM (Fig. 36A). The constriction in the first macroplacoid divides it into two roughly equal, oblique subparts. The constriction in the second macroplacoid is positioned more posteriorly, such that the second macroplacoid consists of a long part (two-thirds of the whole length) and a short, round terminal part (one-third of the whole length; Figs 36E, 43A). Septulum large, almost as long as the second macroplacoid.

Claws of the Hypsibius type, rather stout, with characteristic light-refracting units at the basal portions of the primary branches (Fig. 37). Accessory points on claws I–III barely protruding, in contrast to those on claws IV (compare Fig. 37A with 37B). Primary branches of the posterior claws much longer in comparison to those of external claws (Fig. 37). Lacking pseudolunulae and cuticular bars.

Etymology: The name refers to the presence of granular eyes. Eyes are often large and do not dissolve in Hoyer’s medium. Murray (1906b) decided to highlight this character, which still seems to be the correct decision, because in Pilatobiu s and its ‘maternal’ genus, Diphascon, eyed species are not frequently found. An adjective in nominative singular.

Differential diagnosis: Unfortunately, descriptions of the vast majority of Pilatobius spp. are extremely laconic and do not allow for delineation between similar species. Pilatobius oculatus is most similar to Pilatobius rugocaudatus (Rodríguez Roda, 1952) nom. inq. within the oculatus group (with caudal sculpturing but lacking gibbosities), but they are currently indistinguishable owing to the lack of reliable morphometric or qualitative data (P. rugocaudatus is potentially a younger synonym of P. oculatus, and the vicinity of its type locality in the Pyrenees must be sampled to confirm this). Pilatobius oculatus is easily separated from other species because either they have the entire body sculptured or they have additional dorsal gibbosities (see the key below), and by the presence of light-refracting units at the basal parts of primary branches of external claws (the main difference with regard to P. opisthoglyptus and P.nuominensis Sun et al., 2021, which lack those structures).

Remarks: Dastych (1988) underlined the importance of the primary branch light-refracting units in identifying this taxon. The subspecies Pilatobius oculatus alpius (Mihelčič, 1964) was designated as nomen dubium by Dastych (2015). We agree with this assessment, because the presence of pedal gibbosities on legs IV is unseen in pilatobiins. The second subspecies, Pilatobius oculatus canadensis (Murray, 1910) is insufficiently described, and the most important obscurity regarding this taxon is the absence of eyes, a feature always present in P. oculatus. This inconsistency led us to designating it as nomen dubium. We supress all subspecies of P. oculatus as taxonomically contentious.