Claxtonia wendti
Creators: name: Gąsiorek, Piotr
name: Degma, Peter
name: Michalczyk, Łukasz
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Tardigrada
Heterotardigrada
Echiniscoidea
Echiniscidae
Claxtonia
Claxtonia wendti

description: Re-description of Claxtonia wendti
(Figs 16–20; Table 3; Supporting Information, S1, S2)
Type locality: c. 79°43ʹ54ʹʹN, 10°59ʹ42ʹʹE, 0–10 m a.s.l.: Norway, Svalbard, AmsterdamØya, Smeerenburg. A long-abandoned whaling seưlement.
Neotype locality: c. 77°00ʹN, 15°32ʹE, 350 m a.s.l.: Norway, Svalbard, Spitsbergen, Ariekammen. Neotype (adult female) and two females on the slide NO.448.42.3/4. Four hologenophores preserved on slides NO.448.01–4. All deposited in the Department of Invertebrate Evolution of the Jagiellonian University.
Additional localities (see Table 1 for details): (i) 57°23ʹ15ʹʹN, 2°39ʹ39ʹʹW, 390 m a.s.l.: Scotland, Hill of Foudland, an abandoned slate quarry (sample GB.097). (ii) 60°35ʹ52ʹʹN, 45°22ʹ19ʹʹW, 8 m a.s.l.: Greenland, Ammassivik, tundra (sample GL.044). (iii) 64°04ʹ18ʹʹN, 21°57ʹ30ʹʹW, 15 m a.s.l.: Iceland, Hafnarḩörður, Hellisgerði Park, urban park (sample IS.013). (iv) 69°23ʹ41ʹʹN, 19°55ʹ38ʹʹE, 542 m a.s.l.: Norway, Troms og Finnmark, Lyngen Alps, moraine of Steindalsbreen (sample NO.246). (v) 49°11ʹ51ʹʹN, 20°02ʹ26ʹʹE, 2117 m a.s.l.: Poland, Tatra Mts., Szpiglasowy Wierch, alpine zone (sample PL.376).
Etymology: A patronym honouring A.H. Wendt, the collector of the moss samples containing first examined representatives of the species brought from the Arctic to F. Richters.
Adult females (i.e. þom the third instar onwards; measurements and statistics in Table 3): Body medium-sized and plump (Fig. 16); body colour variable, from light, pale yellow to dark orange. Small red granulate eye spots present in living individuals dissolving rapidly during mounting. Buccal apparatus short, rigid, without stylet supports. Peribuccal cirri with weakly marked cirrophores, flagellum long and thin; cephalic papilla (secondary clava) elongated and conical, of the Echiniscus - type (Figs 17B, 19–20C). Primary clava smaller and thinner than secondary clava; cirrus A of a variable length, but most ossen above 50% of the body length (Figs 18, 19). Its basal part is c. 1.5 times thicker than the rest of flagellum, which is fragile and can be easily broken. Double flagellum embedded on a common cirrophore frequent (Fig. 16A).
Dorsal plate sculpturing comprises densely arranged, rather large epicuticular granules interconnected by evident striae, which separate pseudopores surrounding each granule (but some deviating morphotypes can be observed, see e.g. Fig. 17B); typically no pores or micropores (Figs 16–19)—if present, they are irregularly and sparsely distributed and only in some plates. Intracuticular layer of pillars typically not identifiable in PCM, only rarely developed and mostly in the scapular plate (Fig. 2). Granules may rarely merge and form irregular shapes (Fig. 16D). Cephalic plate with a clearly marked anterior chalice-like incision (Figs 18, 20B); cervical plate identifiable as a clear rectangular belt adjacent to the scapular plate (Figs 16B, 17–20B). Scapular plate uniform, without sutures or incisions (Figs 16–20B). Always only two unipartite, trapezoidal median plates m1–2 of roughly identical sizes. Paired segmental plates I– II with dominating posterior portions; an unsculptured (or with weak protuberances) belt separates anterior and posterior plate portions. Caudal (terminal) plate is the largest element of the armour, several (1–3) faint transversal ridges may constitute a weakly visible carination (Figs 16B, C, 19, 20A). Lateral platelets absent. Venter densely and uniformly granulated with minute intra-/endocuticular pillars; a pair of blurred subcephalic plates may be present (observable as slightly darker in PCM = denser areas at the level of buccal apparatus).
Pulvini on legs thin, but well-identifiable (Figs 17B, 20A); pedal plates finely sculptured with minute intra-/endocuticular pillars (Figs 17B – 18, 20A), which are visible in SEM as slightly protruding capituli (Fig. 20A). First leg pair with a minute spine/ papilla/protuberance embedded on a pedal platelet (Figs 6, 20A, D). Fourth leg pair with a small conical papilla and a fringe composed of many tiny irregular teeth, either merged or separated at their bases (Figs 16B, 17, 18). Claws large and massive, internal ones with robust spurs widely divergent from main branches and positioned at c. 1/3 of the branch (Figs 20D, E).
Adult males (i.e. þom the third instar onwards; measurements and statistics in Supporting Information, S2): Gonopore circular. No other identifiable differences with females.
Juveniles (i.e. the second instar): Qualitatively similar to sexually mature females. Gonopore lacking.
Larvae (i.e. the first instar; measurements and statistics in Supporting Information, S2): Qualitatively similar to later life stages, beside of the aforementioned small dissimilarities in the dorsal plate sculpturing. Two claws per leg, each with already massively developed spurs. Gonopore and anus lacking.
Differential diagnosis: The current species composition of Claxtonia (Degma et al. 2021, Degma and Guideưi 2023), in the light of the presented evidence, is almost certainly artificial. We surmise that the three tropical spp., C. barbarae, C. malpighii, and C. molluscorum, represent another phylogenetic lineage, more related to Viridiscus (Nelson et al. 2020). With caution, C. moniliata (Iharos, 1967), a New Guinean endemic, could be added to this group, based on well-elevated epicuticular granules drawn in the description of that species. None of the four species have striae, which are present in C. wendti. Three other tropical spp., C. aliquantilla (Grigarick et al., 1983), C. marginopora (Grigarick et al., 1983), and C. mosaica (Grigarick et al., 1983) from Venezuela (Grigarick et al. 1983), have too scanty descriptions to hypothesize about their phylogenetic affinity. Claxtonia nigripustula (Horning et al., 1978) and C. vincula (Horning et al., 1978) can be easily told apart from C. wendti by the presence of comparatively larger epicuticular granules interconnected by thicker striae and endocuticular elements merged into uniform matrix in dorsal plates, respectively (Pilato et al. 2005). Among the remaining members of the genus, based on all discussed characters, most likely closely related to C. wendti are: C. capillata, C. corrugicaudata, C. goni, C. mauccii, C. pardalis, and C. pseudowendti. They can be distinguished from C. wendti by the combination of the following traits:
• Claxtonia capillata, an extremely rare, cold stenothermic and West Palaearctic (Dastych 1985, 1988, Maucci 1986) species with dubious records from other parts of the globe (McInnes 1994), has secondary spurs directed upwards on external claws (smooth in C. wendti), and cirri A almost always c. 1.5 times longer than the body length (up to 110% in C. wendti).
• Claxtonia corrugicaudata, an Antarctic species (McInnes 2010), with a questionable record from South America (Roszkowska et al. 2016) based on the information presented in this study, has a clear intracuticular layer of pillars (not reported in the original description, but confirmed asser analysis of paratypes), whereas C. wendti usually does not exhibit this structure, and the epicuticular ridges on the caudal plate are well-developed (usually not visible in PCM at all in C. wendti).
• Claxtonia goni, currently considered a Hawaiian endemic (Degma et al. 2021), has a clear intracuticular layer of pillars (absent or obscure in C. wendti) and evident pores (typically absent in C. wendti).
• Claxtonia mauccii, native to North America (Ramazzoưi and Maucci 1983, Mitchell and Romano 2007), has larger epicuticular granules with more massive striae, receptors on legs II–III, and more delicate spurs compared with C. wendti.
• Claxtonia pardalis, found only in the Italian Maritime Alps (Degma and Schill 2015), has a clear intracuticular layer of pillars (absent or obscure in C. wendti) and evident pores (typically absent in C. wendti).
• Claxtonia pseudowendti, an Antarctic species (Dastych 1984), has evident pores distributed in all plates (typically absent in C. wendti; if present, distributed irregularly, sparsely, and only in some plates).
Remarks: Pores reported in C. wendti in Degma et al. (2021) and in this re-description have never been confirmed with SEM for this echiniscid group, despite analysing numerous (more than 50) individuals. Claxtonia nigripustula and C. vincula from the Southern Hemisphere (Horning et al. 1978) have an uncertain phylogenetic affinity and they may represent a different lineage than C. wendti.
description: Published as part of Gąsiorek, Piotr, Degma, Peter & Michalczyk, Łukasz, 2024, Hiding in the Arctic and in mountains: a (dis) entangled classification of Claxtonia (Heterotardigrada: Echiniscidae), pp. 60-86 in Zoological Journal of the Linnean Society 200 (1) on pages 75-81, DOI: 10.1093/zoolinnean/zlad029, http://zenodo.org/record/10469722