Diphascon prorsirostre, Thulin, 1928

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 : 13-22

D. cf. prorsirostre ; Tranemåla, Sweden; Jönsson (2003).

Adropion prorsirostre ; Battle Hill, Huntly, Aberdeenshire; Invermoriston, Loch Ness, Highland; Slug Road, Stonehaven, Aberdeenshire, Scotland; Blagden et al. (2020). Guidettion prorsirostre ; Scotland; Gąsiorek and Michalczyk (2020).

Material examined: 48 individuals in total (for details, see Supporting Information, Table S1).

Neotype material: Neotype and 30 specimens (slides GB.062.01– 06) from Scotland, Little Oxen Craig, Bennachie (57°17 ʹ 35″N, 2°33 ʹ 40″W; 507 m a.s.l.), moss from rowan tree bark ( Sorbus aucuparia L.), 5 October 2015, Blagden coll., are deposited in the Institute of Zoology and Biomedical Research, Jagiellonian University, Kraków. Seven specimens (slide GB.062.07; NHMD Catalogue number 1651665) are deposited in the Natural History Museum, University of Copenhagen, Denmark .

Comparative material: Scotland, Insch (57°20 ʹ 32″N, 2°38 ʹ 44″W; 268 m a.s.l.), rural vicinity, lichen ( Cladonia ) from rock, 19 December 2014, Blagden coll. (three specimens) ; Hill of Foudland (57°23 ʹ 15″N, 2°39 ʹ 39″W; 350 m a.s.l.), old slate quarry, moss from tree, 26 September 2015, Blagden coll. (10 specimens) ; Cabrach , Foot of The Buck (57°18 ʹ 31″N, 2°57 ʹ 18″W; 427 m a.s.l.), pine needles from soil, 26 September 2015, Blagden coll. (one specimen) ; Drum Castle , Drumoak (57°05 ʹ 42″N, 2°20 ʹ 16″W; 114 m a.s.l.), rural vicinity, leaf litter ( Quercus robur ) from soil, 5 September 2016, Blagden coll. (two specimens) ; Creag Meagaidh (56°57 ʹ 03″N, 4°36 ʹ 09″ W; 1100 m a.s.l.), mountain grassland, lichen ( Peltigera Willd. ) from rock, 1 September 2016, Blagden coll. (seven specimens) ; Norway, RingsvassØya , Hansnes (69°57 ʹ 37″N, 19°36 ʹ 23″E; 3 m a.s.l.), forest, moss from soil, 3 Septmeber 2015, Hlebowicz coll. (six specimens) ; Poland, Kamienna Góra (50°46 ʹ 39″N, 16°03 ʹ 22″E; 490 m a.s.l.), urban park, moss from tree trunk, 5 September 2015, Przybycień coll. (six specimens) .

Redescription: Body small to medium-sized ( Table 4), elongate and white; cuticle smooth, without pores, wrinkling or granulation ( Fig. 12A). Cribriform areas not visible under PCM. Legs short and plump. Eyes absent in live animals. Buccopharyngeal apparatus of the Adropion type ( Figs 12A, 13A, B). The OCA invisible under PCM ( Fig. 13A), but visible in SEM as one row of conical teeth ( Fig. 13C). The AISMs flat, but rather narrow ( Fig. 13A, D). Furcae of the Hypsibius type ( Fig. 13E). Buccal tube transitions smoothly into the annulated pharyngeal tube ( Fig. 13A, B, F), with single, widely separated annuli ( Fig. 13F, G). In its posterior part, the pharyngeal tube is devoid of annulation ( Fig. 13H). Small pharyngeal apophyses present ( Fig. 13A, B, H). Pharynx oval ( Fig. 13A; non-deformed pharynx length-to-width ratio: 1.7–2.5). Macroplacoid length sequence 1 = 2 <3, all elongate and thin, with smooth margins. The third macroplacoid two times longer than the second ( Fig. 13H). Lacking microplacoid and septulum.

Claws of the Hypsibius type, small, with slightly widened bases and slightly protruding accessory points on the primary branches ( Fig. 14). The primary branches are much longer than the secondary branches. Secondary branches markedly curved. Pseudolunulae and cuticular bars at the claw bases absent ( Fig. 14).

Etymology: From Latin prorsus = having a forward projection, and rostrum = snout. The mouth opening is placed at the end of the snout, as a continuation of the main body axis in this species. An adjective in nominative singular.

Differential diagnosis: Depending on the position of a specimen (i.e. dorsoventral or lateral projection), the mouth opening may be described as terminally or more ventrally positioned in G. prorsirostre . In agreement with the observations and opinions of other tardigradologists ( Cuénot 1932, Marcus 1936, Ramazzotti and Maucci 1983), we do not recognize the distinction between Guidettion arduifrons ( Thulin, 1928) , described based on animals collected in Lapland and Siberia, and G. prorsirostre ( Fig. 12B, C), thus we designate the former as nomen inquirendum. It is possible that G. arduifrons is a valid species, but the current morphological data prevent its identification. Guidettion carolae ( Binda & Pilato,1969) is morphologically identical to G. prorsirostre , as redescribed above, thus it is designated as synonym novum. Of the remaining species with only macroplacoids in the pharynx, the most similar to G. prorsirostre are Guidettion clavatum ( Bartoš, 1935) and Guidettion modestum ( Binda et al., 1984) (see the key to Guidettion spp. ). However, G. clavatum exhibits granulated caudal cuticle and G. modestum lacks pharyngeal apophyses, characteristics sufficient to separate both taxa from G. prorsirostre . The recently described Guidettion vexatum ( Pilato et al., 2017) does not appear to be sufficiently differentiated from G. prorsirostre . Its description was based on a small number of individuals, and several of the morphometric characters, in addition to the ‘small dots on legs’ (as reported in the original description, i.e. a potential form of granulation), are not identifiable in any of the photomicrographs. These features, which were used to delimit G. vexatum from G. prorsirostre , can be questioned easily, owing to the increased accuracy of measurements provided in the present redescription of G. prorsirostre . Thus, we designate G. vexatum as nomen inquirendum, pending the verification of its validity.

Taxonomic key to the genus Guidettion Remark: Guidettion arduifrons nom. inq. is not included in the key, owing to the unavailability of traits differentiating it from G. prorsirostre .

1. Macroplacoids granular ........................................................................................................................................ Guidettion montigenum

– Macroplacoid bar-like .................................................................................................................................................................................. 2

2. Caudal cuticular granulation present ....................................................................................................................... Guidettion clavatum

– Caudal cuticular granulation absent ......................................................................................................................................................... 3

3. Pharyngeal apophyses absent .................................................................................................................................. Guidettion modestum

– Pharyngeal apophyses present ................................................................................................................................................................... 4

4. pt of SSIP> 66% ...................................................................................................................................................... Guidettion prorsirostre

– pt of SSIP <66% ......................................................................................................................................... Guidettion vexatum nom. inq.