Echiniscus merokensis 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 : 36-37

13. Echiniscus merokensis Richters, 1904

Figures 18–20

Synonyms

Echiniscus batramiae Iharos, 1936 syn. nov.

Echiniscus columinis Murray, 1911 syn. nov.

Echiniscus iharosi Rudescu, 1964 : Ramazzotti & Maucci (1983)

Echiniscus jagodici Mihelčič, 1951 syn. nov.

Echiniscus laterospinosus Rudescu, 1964 syn. nov.

Echiniscus merokensis suecicus Thulin, 1911 syn. nov.

Echiniscus simba Marcus, 1928 : Gąsiorek et al. (2019b)

Locus typicus: Amsterdamøya ( Svalbard) and Merok ( Norway) ( Richters 1904b).

Etymology: Referring to the type locality in Merok. An adjective in nominative singular.

Shortened description: Small to medium-sized (ca. 170–230 μm). Body appendage configuration A-(B)-(Bd)- C-Cd- D-Dd- E, with appendages B often and Bd usually absent. An enormous variability of chaetotaxy: all lateral appendages are long cirri ( Fig. 18 ), but dorsal appendages can be both long, rigid spines ( Figs 18A, D ), or reduced spicules ( Figs 18B–C ). Asymmetries frequent. Dorsal plate sculpturing embraces (1) dominant large pseudopores and (2) endocuticular pillars protruding to epicuticle as granules connected by striae (the merokensis type). Caudal plate usually with unsculptured epicuticular ridges forming a cross ( Figs 18B–D , arrowheads). Dentate collar IV with numerous irregular teeth. Claws of a moderate size with respect to the body length, with primary spurs closely positioned to claw bases, but clearly divergent from their bases and easily identifiable. Larvae with a simplified sculpturing that comprises only endocuticular pillars and single pores, distributed mainly in scapular and caudal plates. Body appendage formula A–E ( Fig. 19 ).

Phylogenetic position: The species belongs within the merokensis group, being sister to E. pellucidus Gąsiorek et al., 2021 (Figs 1–2).

Remarks:The species is cosmopolitan( Roszkowska et al.2018),usually exhibiting cold stenothermic preferences. An extensive taxonomic literature is devoted to the distinction between E. merokensis and E. quadrispinosus (for details see e.g. Lattes & Gallelli 1972; Lattes 1975; Ramazzotti & Maucci 1983). This is another example of how deceiving an identification based on chaetotaxy can be, especially that the two species are not similar in the dorsal sculpturing (compare Figs 18 and 24A–B ) and they are not related (Figs 1–2). However, the remarkable intraspecific variability of E. merokensis historically caused much confusion ( Ramazzotti 1958; Ramazzotti & Maucci 1983), and we address this herein by establishing five new junior synonymies. The subspecies E. merokensis suecicus Thulin, 1911 syn. nov. is abolished given that the presence of cirrus B, the only distinguishing criterion from E. merokensis merokensis , is variable among many Echiniscus spp. ( Gąsiorek et al. 2017), thus cannot be treated as reliable. Echiniscus batramiae Iharos, 1936 syn. nov. exhibits an identical chaetotaxy and dorsal sculpturing ( Fig. 20 ) as E. merokensis . Echiniscus columinis Murray, 1911 syn. nov. also falls within the scope of intraspecific variability of E. merokensis , as noted before ( Ramazzotti & Maucci 1983). Echiniscus jagodici Mihelčič, 1951 syn. nov., with previously expressed doubts regarding its validity ( Dastych 2015), is most likely an aberrant form of E. merokensis , with appendages C and Dd lacking. Lastly, E. laterospinosus Rudescu, 1964 syn. nov. also has an identical chaetotaxy and dorsal sculpturing as E. merokensis , and must be synonymised accordingly. By our designation, E. merokensis should be regarded as monotypic.

Figures

FIGURE 18. Echiniscus merokensis from Scotland (PCM): A—no appendage in position B (E. merokensis merokensis), B— cirrus B present (E. merokensis suecicus syn. nov.), C—cirrus B and spine Bd present (a rare morphological variety described by Ramazzotti in 1958), D—cirri B and Bd present (a newly reported form). Arrowheads indicate epicuticular ridges on the caudal plate. Scale bars = 20 μm.

FIGURE 19. Echiniscus merokensis from Scotland (PCM): larva. Scale bar = 20 μm.

FIGURE 20. Echiniscus batramiae syn. nov. (PCM, syntype): A—scapular plate, B—median body portion. Scale bars = 10 μm.

FIGURE 24. Echiniscus quadrispinosus from Germany—cephalic region:A—scapular plate sculpturing in upper magnification (PCM), B—scapular plate sculpturing in lower magnification (PCM), C—scapular plate sculpturing (SEM), D—cephalic appendages and subcephalic plates (SEM). Scale bars = 20 μm.