Pilatobius bullatus (Murray, 1905)

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 : 40-42

Pilatobius bullatus (Murray, 1905) in Murray (1905a)

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

Amended description: Eyes absent in live individuals. Body cylindrical ( Fig. 33A, B ), with eight rows of poorly elevated, hemispherical gibbosities (VIII:2-2-2-2-2-2-2-2) that are not covered with sculpturing ( Fig. 33A, C ). The first row of gibbosities is at the level of legs I, whereas the last row is slightly divergent from the remainder and located at the base of leg IV ( Fig. 33A ). Dorsal sculpturing in the form of irregular polygons ( Fig. 33C ), extending to the lateralmost body portions including legs IV, but absent on legs I–III and venter ( Fig. 33B ). Legs IV with sculpturing. Buccopharyngeal apparatus of the Pilatobius type ( Fig. 33B ): OCA not visible under PCM; a large DABT at the border between the rigid buccal tube and annulated pharyngeal tube; furcae of the Hypsibius type; pharyngeal apophyses large and prominent; pharynx semicircular, with two bar-like macroplacoids: the first longer than the second (2 <1), and a septulum. The first macroplacoid with a slight anterior constriction, whereas the second macroplacoid with a subterminal constriction ( Fig. 43B ).

Claws of the Hypsibius type ( Fig. 34 ). Primary branches of the external, anterior, and posterior claws with a swollen proximal part; light-refracting units absent. Accessory points divergent only on the primary branches of the posterior claws ( Fig. 34B ). Pseudolunulae present. Internal cuticular bars I–III long and terminating at the pseudolunulae of the internal claws ( Fig. 34A ). Claws IV with three types of short bars: (i) posterior; (ii) anterior, partly overlapping with pseudolunulae; and (iii) orthogonal (reported in specimens representing this or closely related species for the first time by Tumanov et al. 2022; Fig. 34B ).

Remarks: We did not find a sufficient number of specimens to provide a modern redescription with DNA barcodes and morphometric data, but the factual qualitative characteristics provided above for animals collected in terra typica can serve as a starting point for the correct identification of this species. Specimens from Ireland ( Blagden et al. 2020) and Russia ( Tumanov et al. 2022) do not conform fully with the morphotype described herein because they exhibit sculpturing of the gibbosities, not detectable under LCM in specimens from Scotland and, consequently, are most likely to represent a closely related species. All three types of cuticular bars were first described by Dastych (1988) for Polish representatives of P. bullatus . He drew a reticulum on the gibbosities of these specimens, which is, however, absent in the Scottish population analysed here. There is a possibility that this character is variable and prone to observation errors; this could be clarified with a SEM examination. Dastych (1988) also hypothesized that Pilatobius patanei ( Binda & Pilato, 1971) is synonymous with P. bullatus . Although the main criterion used to discriminate between the species (polygonal vs. supposedly granular sculpturing) was demonstrated to be invalid, the original description of P. patanei contains a vital diagnostic criterion: large granular eyes. Dastych (1988) questioned the utility of eyes in separating hypsibiid species, because he reported that they may be either absent or present in the same species, but our data indicate otherwise, i.e. that individuals belonging to one species either have or do not have eyes. Additionally, Tumanov et al. (2022) argued for the validity of P. patanei based on genetic differences between specimens identified as P. patanei ( Bertolani et al. 2014) and P. bullatus (therein). We, therefore, keep P. bullatus and P. patanei as distinct taxa; nevertheless, this issue requires further analyses to dispel doubts that arose around P. patanei . In contrast, P. trachydorsatus is indistinguishable from P. bullatus and designated here as synonym novum.

Figures

Figure 33. General morphology of Pilatobius bullatus (Murray, 1905) in Murray (1905a) (PCM, topotypes): A, dorsal view; B, ventral view; C, close up of dorsal gibbosities and sculpturing.Scale bars are in micrometres.

Figure 34. Claws of Pilatobius bullatus (PCM, topotypes):A, claws II; B, claws IV. Black arrowheads indicate internal and posterior bars, white arrowhead indicates anterior bar, and empty white arrowhead points out a pseudolunule.Scale bars: 10 μm.

Figure 43. Various Pilatobiinae, morphology of pharyngeal structures (SEM): A, P.oculatus; B, P.bullatus; C, P.ramazzottii; D, P.recamieri (Richters, 1911); E, P.patanei (Binda & Pilato, 1971), lateral view; F, P.patanei, dorsal view. Scale bars: 5 μm.