Echiniscus spiniger Richters, 1904

Gąsiorek, Piotr & Vončina, Katarzyna, 2023, Atlas of the Echiniscidae (Heterotardigrada) of the World-part I: West Palaearctic Echiniscus species, Zootaxa 5344 (1), pp. 1-72 : 46-47

17. Echiniscus spiniger Richters, 1904

Figures 28–29 , 39

Locus typicus: Sweden, Gotland, Visby.

Additional localities: (1) Switzerland, Fribourg ( Rahm 1928); (2) Romania: Suceava County, Câmpulung Moldovenesc, the Rarău Massif, the Giumalău Massif and Hunedoara County, the Retezat Massif, Gura Zlata ( Rudescu 1964); (3) Poland: vicinity of Chęciny, nature reserve Przełom Białki near Krempachy, nature reserve Wąwóz Homole ( Dastych 1988); (4) 56°37’10”N, 16°30’6”E, 43 m asl: Sweden, Öland, Skogsby, Ecological Research Station of Uppsala University ( Jönsson 2007); (5) 49°14’23’’N, 19°51’44’’E, 1124 m asl: Poland, the Tatras, Kościeliska Valley, Raptawicka Cave ( Gąsiorek & Degma 2018); (6) 56°52’N, 16°39’E, 10 m asl: Sweden, Öland, Borgholm and 56°44’43’’N, 16°38’33’’E, 29 m asl: Sweden, Öland, Ismantorp ( Gąsiorek & Michalczyk 2020); (7) Ireland, Clare county, vicinity of Bellharbour ( DeMilio et al. 2022). New verified records: (8) France, Nouvelle-Aquitaine, Les Eyzies; moss from a roof coll. on 27 th July 1961; several specimens, incl. larvae, mounted in polyvinyl lactophenol (the Ramazzotti collection, not included in Ramazzotti & Maucci 1983); (9) Italy: Abruzzo, Tagliacozzo, Monte Amaro, Maiella ( Maucci 1986) and Umbria, Monte Serva Santa (the Maucci collection, not included in Maucci 1986).

Etymology: From Latin spiniger = thorn-bearing, which underlines the presence of numerous spiniform trunk appendages. An adjective in nominative singular.

Shortened description. Small to large (ca. 160–350 μm). Body appendage configuration A-B-C-Cd- D-Dd- E, with occasional asymmetries. All appendages spiniform and smooth. Lateral spines similar in length to prominent dorsal spines ( Fig. 28 ). Dorsal plate sculpturing of the spinulosus type, with large pores only rarely containing faint intracuticular rings ( Figs 29A–C , arrowheads). Anterior portions of paired segmental plates with reduced endocuticular matrix, which results in a different appearance of pores and visible endocuticular pillars ( Fig. 29B ). Large and richly sculptured pedal plates ( Fig. 28 ). Subcephalic plates present in adults ( Fig. 29D ). Dentate collar IV typically with few (7–8) large and widely spaced teeth ( Fig. 28 ). Claws large, massive, and heteronych: primary spurs I–III small compared with overall size of a branch and positioned more closely to their bases ( Fig. 29D ) than spurs IV that are larger, more divergent from branch and positioned higher on each internal claw.

Phylogenetic position: Echiniscus spiniger is nested among the sequenced populations of E. spinulosus , clearly being not well-differentiated genetically (Figs 1–2). The differences in COI are also minor (interspecific p -distance = 2.0–2.4% vs intraspecific variability of E. spinulosus = 0.8–2.4%).

Remarks:The purported worldwide distribution of this species( McInnes1994)has already been rightly questioned (e.g. Pilato et al. 2005), and all records outside the Palaearctic region are almost certainly misidentifications. We provided a summary of verified records of E. spiniger based on trustworthy records and re-examination of historical material ( Fig. 39 ). The species was notoriously confused with E. spinulosus even by experienced researchers, like Maucci, whose records of E. spiniger refer mostly to E. spinulosus (see below). Dastych (1988) was the first to note the need for revision of the spinulosus complex, but the specimens found in the course of his studies on the Polish tardigrade fauna conform with the morphotype of E. spiniger . The lack of genetic distinctiveness of E. spiniger (Figs 1–2) supports Cuénot’s (1932) supposition that it is a junior synonym of E. spinulosus , however, we decided not to synonymise these two species yet because of two reasons: (1) the morphotype corresponding with E. spiniger (all trunk spines of similar lengths) always occurs separately, not intermixed with populations of E. spinulosus (lateral spicules several times shorter than dorsal spines), and (2) sequencing several more populations of E. spiniger from other localities would be desirable to infer whether the uniformity of E. spiniger and E. spinulosus is consistent and stable. Then, E. spiniger could be put in synonymy.

Figures

FIGURE 28. Echiniscus spiniger from Sweden (PCM, female in dorsal view). Scale bar = 50 μm.

FIGURE 29. Echiniscus spiniger from Sweden—morphological details (PCM):A—scapular plate, B—paired segmental plate I, C—caudal plate, D—claws I and subcephalic plates. Arrowheads indicate dark intracuticular rings. Scale bars = 20 μm.

FIGURE 39. Reliable records of E. spiniger from Europe.