Hypsibius oculatus (Murray, 1906)

Gąsiorek, Piotr, Blagden, Brian, Morek, Witold & Michalczyk, Łukasz, 2024, What is a ‘ strong’ synapomorphy? Redescriptions of Murray’s type species and descriptions of new taxa challenge the systematics of Hypsibiidae (Eutardigrada: Parachela), Zoological Journal of the Linnean Society 202 (1), pp. 1-63 : 45-47

publication ID	https://doi.org/ 10.1093/zoolinnean/zlad151
publication LSID	lsid:zoobank.org:pub:044A402-2A0F-4135-9410-7DE081CB11C4Corresponding
persistent identifier	https://treatment.plazi.org/id/03AF87C4-A615-FF9C-ADD4-6A53FAFD8C41
treatment provided by	Plazi
scientific name	Hypsibius oculatus
status

Treatment

Hypsibius oculatus View in CoL ; 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 GoogleMaps .

Redescription: Body small to medium in size ( Table 12), elongate and tapering anteriorly ( Fig. 35A View Figure 35 ), 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 View Figure 35 ). 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 View Figure 35 ). Dorsum strongly sculptured in its posterior part ( Fig. 35C View Figure 35 ); 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 View Figure 35 ). Sculpture composed of numerous irregular polygons. Legs long, devoid of sculpturing or pedal gibbosities ( Fig. 35A View Figure 35 ). Eyes always present in living animals, consisting of a few large granules merged into one eyespot ( Fig. 36A View Figure 36 ). Long buccopharyngeal apparatus of the Pilatobius type ( Fig. 36A, B View Figure 36 ). The OCA not visible under PCM ( Fig. 36A View Figure 36 ). 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 View Figure 36 ). Annuli vanish ~2 μm before the pharyngeal apophyses ( Fig. 36D View Figure 36 ), which are large ( Fig. 36A, E View Figure 36 ). Pharynx circular ( Fig. 36A View Figure 36 ). Macroplacoid length sequence 2 <1, both with constrictions detectable under PCM ( Fig. 36A View Figure 36 ). 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 View Figure 36 , 43A View Figure 43 ). 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 View Figure 37 ). Accessory points on claws I–III barely protruding, in contrast to those on claws IV (compare Fig. 37A View Figure 37 with 37B). Primary branches of the posterior claws much longer in comparison to those of external claws ( Fig. 37 View Figure 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.