Raribius minutissimus Gąsiorek & Michalczyk, 2024

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 : 36-38

Raribius minutissimus Gąsiorek & Michalczyk sp. nov.

Raribius sp. nov.; Scotland; Gąsiorek and Michalczyk (2020).

ZooBank registration: urn:lsid:zoobank.org:act:EB412AD2-2AD0-4F57-BA97-07D3D287D33B

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

Type material: Holotype (slide GB.043.10 ) and five paratypes (slides GB.043.08–9 , 11, and GB.059.01–2 ) from Scotland, Drumoak, Drum Castle (57°5 ʹ 42″N, 2°20 ʹ 16″W, 114 m a.s.l.), leaf litter (mixed Quercus robur + Rhododendron ) collected from soil, April and September 2016, Blagden coll., are deposited in the Institute of Zoology and Biomedical Research, Jagiellonian University, Kraków. Hologenophores were retrieved in a good condition and included in the type material owing to an overall paucity of individuals.

Comparative material: Raribius pawlowskii ; Poland, Polana pod Wołoszynem , Tatra Mountains, lower forest zone, mosses from rocks, February 1971, a paratype in the collection of the Zoological Museum, Jagiellonian University ; Italy, vicinity of Rugolo, Treviso province , detailed data unspecified, collection of the Department of Life Sciences, University of Modena and Reggio Emilia .

Description: Body small ( Table 11 ), elongate and slightly narrowed in its anterior part ( Fig. 31A ). Head blunt. Body whitish to almost translucent. Cuticle smooth, without pores, wrinkling, or granulation. Cribriform areas not visible under PCM. Legs very short and weakly delimited from the trunk. Eyes absent in live animals. Buccopharyngeal apparatus of the Raribius type ( Fig. 31B ). The OCA not visible under PCM. Furcae of the Itaquascon type, with triangular, large apices. Stylet supports S-shaped. Pharyngeal apophyses absent; instead, the pharyngeal tube is slightly enlarged at its posterior end. Pharynx almost perfectly round, with a single rectangular macroplacoid with smooth margins.

Claws of the Hypsibius type, minute and slender, with accessory points not visible under PCM ( Fig. 31A, C ). Pseudolunulae, cuticular bars, and septa absent.

Etymology: From the Latin minutissimus = the smallest. The species is one of the smallest eutardigrades. An adjective in nominative singular.

Differential diagnosis: Raribius minutissimus has short rectangular macroplacoids, whereas the pharynx is devoid of placoids in R. pawlowskii . No difference was detected in claw morphology ( Fig. 32 ). Raribius globuliferus ( Abe & Ito, 1994) has internal cuticular bars at the claw I–III bases and posterior bars ( Guidetti et al. 1999), whereas both types of bars are absent in R. minutissimus .

Figures

Figure 31. Detailed morphology of Raribius minutissimus sp. nov. (PCM): A, holotype in ventral view; B, buccopharyngeal apparatus in toto; C, claws IV.Scale bars are in micrometres.

Figure 32. Raribius pawlowskii (Węglarska, 1973) (PCM): A, claws II (an individual from Rugalo, Italy); B, claws III (an individual from Rugalo, Italy); C, claws IV (paratype). Scale bars: 10 μm.