Echiniscus blumi Richters 1903

4. Echiniscus blumi Richters, 1903

Figure 4A

Synonyms

Echiniscus bisetosus Heinis, 1908: Gąsiorek et al. (2019b)

Echiniscus blumi schizofilus Bartoš, 1941 syn. nov.

Echiniscus mediantus Marcus, 1930: Gąsiorek et al. (2019b)

Echiniscus ramazzottii Binda & Pilato, 1969: Maucci (1985)

Echiniscus trojanus Maucci, 1973 syn. nov.

Terra typica: Spitsbergen (a general reference) and Merok (Norway) (Richters 1903); Klaas-Billen Bay, Isfjord, Spitsbergen (Richters 1904b). The species description was published independently in two separate papers (Richters 1903, 1904b).

Etymology: The name commemorates J. Blum. A noun in the genitive singular.

Shortened description: Medium-sized to large (ca. 250–450 μm, typically 300–400 μm). Body appendage configuration A-(B)- C-Cd- D-Dd- E (Fig. 4A); generally cirrous appendages in positions B, C, Cd , D, and spines in positions Dd , E, but a variety of intermediate stages can be observed, with some appendages frequently absent or lacking asymmetrically. Overall, chaetotaxy unstable. Dorsal plate sculpturing comprises densely arranged pores with thick epicuticular edges in the form of polygons (Fig. 5A). Pedal plates weakly sculptured. Subcephalic and genital plates may be present in sexually mature females. Claws large; internal ones with primary spurs directed downwards, and external ones with secondary and sometimes even tertiary spurs directed upwards.

Phylogenetic position: Echiniscus blumi is firmly located at the base of the Echiniscus phylogenetic tree (Figs 1–2).

Remarks:Problems with species delimitation in the blumi-canadensis complex are almost as old as tardigradology itself (Ramazzotti & Maucci 1982), and constitute a prime example of how fallacious the sole usage of chaetotaxy can be in the Echiniscidae. Guil (2008) summarised all transitional forms between morphotypes recognised as species at that time, concluding that basically they represent a morphological continuum, which agrees with findings of previous researchers (Ramazzotti & Maucci 1983; Maucci 1985). A single molecular study on the populations from central Iberian Peninsula revealed the discordance between morphology and COI barcode, leading to a suspicion that cryptic speciation may take place in the case of this group (Guil & Giribet 2009). Based on ample comparative material (Argentina, Canary Islands, France, Georgia, Greenland, Iceland, Italy, Kazakhstan, Kyrgyzstan, North America, South Africa, Spain, Svalbard, Tanzania) deposited in our Department, we hypothesise that it is unlikely that E. canadensis Murray, 1910 and E. trisetosus Cuénot, 1932 will stand the test of time, but we temporarily left them in the list of valid species for two reasons: (1) type locality of E. canadensis is extra-European, and should be sampled in order to obtain DNA barcodes; and (2) these are the only two species of the complex that can be found as populations independent from the admixture of E. blumi. Irrespectively of the status of both species, we express our conviction that if there are any morphological differences between potentially cryptic lineages within the blumi-canadensis complex, they will be mostly quantitative, not qualitative. The application of geometric morphometry could aid in species delineation in such case (Fontoura & Morais 2011). Echiniscus marleyi Li, 2007 nom. inq. also belongs in the blumi-canadensis complex and is probably synonymous with E. blumi, too. We establish two new synonymies for E. blumi. The first is E. blumi schizofilus Bartoš, 1941 syn. nov., described to accommodate individuals with doubled appendages, mainly in lateral positions, or with forked cirri. Such atypical forms are, however, common within populations of E. blumi, as there is a great variation in the development of cirri. Moreover, another example of a synonymous morphotype has already been established for a phenotype with aberrant appendages B (Maucci 1985). Consequently, E. blumi becomes a monotypic species. The second species is Echiniscus trojanus Maucci, 1973 syn. nov. (Figs 5B–F), which could be differentiated from E. blumi based on the absence of cirri B and the development of spine E. Both traits are, however, variable within the blumi-canadensis complex, and cannot be treated as valid.