Platicrista horribilis Kaczmarek & Michalczyk, 2003

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 : 31-36

Platicrista horribilis Kaczmarek & Michalczyk, 2003

Material examined: 25 individuals in total (for details, see Supporting Information, Table S1).

Amended description: The OCA not visible under PCM; simple pharyngeal annulation composed of tightly arranged single annuli; pharyngeal apophyses absent ( Fig. 27A). Large claws of the Hypsibius type ( Fig. 27B–D). Accessory points divergent from both primary and secondary branches of all claws. Pseudolunulae present, indented only on legs IV. Internal, anterior, and posterior claw bases with delicate indentations ( Fig. 27B–D). Cuticular bars absent.

Remarks: The indentation of claw IV bases is not always as well developed as depicted in the original description ( Kaczmarek and Michalczyk 2003). A more comprehensive morphometric dataset for the species is presented in Table 9.

Platicrista nivea Gąsiorek sp. nov.

ZooBank registration: urn:lsid:zoobank.org:act:3988853F-DDB5-4217-8293-701E05D226BD

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

Type material: Holotype (slide TW.006.07) from Taiwan, Snow Mountain (Xueshan), East Peak (24°23 ʹ 18″N, 121°15 ʹ 39″E; 3200 m a.s.l.), moss from rock in alpine grassland, 10 February 2020, Dreyer coll., and two paratypes (slides TW.008.14 and TW.008.15) from Taiwan, Snow Mountain (Xueshan), North Peak (24°23 ʹ 51″N, 121°14 ʹ 04″E; 3700 m a.s.l.), moss from rock in alpine grassland, 10 February 2020, Dreyer coll., are deposited in the Institute of Zoology and Biomedical Research, Jagiellonian University, Kraków.

Description: Body massive ( Table 10), white and elongated, with blunt cephalic part ( Fig. 28). Cuticle without pores, but with both irregular wrinkling and distinct, minute granulation in the caudal body part ( Fig. 29). Cribriform areas identifiable under PCM ( Fig. 29A). Legs short and plump; legs IV poorly delimited from the trunk ( Fig. 28). Eyes absent in unmounted animals. Buccopharyngeal apparatus of the Platicrista type ( Fig. 30A): OCA not visible under PCM; annulation of the pharyngeal tube simple (single bifurcations visible) and comprising tightly merged annuli; stylet supports embedded at the border between buccal and pharyngeal tube; furcae of the Platicrista type; pharyngeal apophyses absent; pharynx oval, with two bar-like macroplacoids: the first much shorter than the second one (1 <2).

Claws of the Hypsibius type, large and slender ( Figs 28, 30B). Accessory points divergent from all claw branches. Indentation of claw bases absent. Septa between claw parts absent. Pseudolunulae present, but clearly discernible only under anterior claws ( Fig. 28). Cuticular bars absent.

Etymology: From the Latin niveus = snowy, referring to the type locality in Snow Mountain (Taiwan). An adjective in nominative singular.

Differential diagnosis: There are two congeneric species with strong dorsal sculpturing: P. brunsoni and P. cheleusis . Platicrista nivea can be differentiated from them based on differences in the type of sculpturing (minute granules restricted to the caudal part in P. nivea vs. polygonal tubercles covering the entire dorsum in both species) and:

• for P. brunsoni , the presence of internal bars II–III (absent in P. nivea vs. present in P. brunsoni );

• for P. cheleusis , the presence of internal and median bars I–III and posterior bars (absent in P. nivea vs. present in P. cheleusis ).

Platicrista angustata and P. carpathica have a similar-looking dorsocaudal cuticle; see above for differentiation.

Composition of Platicrista

With body lengths exceeding 800–900 μm, several species of Platicrista are among the largest eutardigrades and are the largest hypsibiids. In light of this, the only species described from the tropics, P. borneensis , is evidently the most divergent in terms of adult body size (<< 500 μm) and buccopharyngeal tube, which is in agreement with its sister position with respect to all other Platicrista spp. ( Fig. 2). The two Nearctic species, P. brunsoni and P. cheleusis , evolved a surprisingly similar type of dorsal sculpturing and thus might be closely related. We sequenced an additional, unnamed species from the Peruvian Andes that is a sister taxon of P. angustata ( Fig. 2). It exhibits a weakly developed reticulum on the caudal body portion, not the irregular wrinkling present in P. angustata or P. carpathica .

is assigned a nomen inquirendum status given that the description was shown to contain an error (the presence of a microplacoid was not confirmed; Marley 2006) and, with an example of I. serratulum , we show here that the presence of ‘spurs’ on posterior claw bases is a morphological aberration, not a reliable taxonomic character. Finally, the claw IV bases of both P. itaquasconoide and P. angustata are indented. Consequently, given that the species lacks any morphological characteristics separating it from P. angustata , it is excluded from the key.

1. Cuticular bars on legs present .................................................................................................................................................................... 2 – Cuticular bars on legs absent ...................................................................................................................................................................... 5 2. Cuticle sculptured with polygonal tubercles ........................................................................................................................................... 3 – Cuticle smooth .............................................................................................................................................................................................. 4 3. Internal bars I absent, claw IV bases indented ........................................................................................................ Platicrista brunsoni – Internal bars I present, claw IV bases smooth .......................................................................................................... Platicrista cheleusis 4. Only median and posterior bars present, pt of the stylet insertion point <90% .......................... Platicrista borneensis sp. nov. – Only internal bars I–III present, pt of the stylet insertion point> 95% .............................................................. Platicrista ramsayi 5. Buccal tube striation present ............................................................................................................................................ Platicrista aluna – Buccal tube striation absent ........................................................................................................................................................................ 6 6. Caudal granulation present only on the lateralmost portions of the caudal trunk ........................ Platicrista carpathica sp. nov. – Caudal granulation absent or present on the entire caudal trunk ....................................................................................................... 7 7. Claws IV with smooth bases .............................................................................................................................. Platicrista nivea sp. nov. – Claws IV with indented bases .................................................................................................................................................................... 8 8. Pseudolunulae IV smooth ......................................................................................................................................... Platicrista angustata – Pseudolunulae IV indented ........................................................................................................................................ Platicrista horribilis