Echiniscus becki (Schuster and Grigarick, 1966)

Gąsiorek, Piotr, 2023, Eventually tested: Phylogenetic position of “ Testechiniscus ” meridionalis (Murray, 1906) (Heterotardigrada) revealed, Zoologischer Anzeiger 304, pp. 49-60 : 55

3.3. Revised morphological characters for Echiniscus becki and Echiniscus laterosetosus

An analysis of the type material of E. becki revealed new traits crucial in determining its phylogenetic position. The dorsal plate sculpturing comprises tightly arranged, polygonal endocuticular pillars ( Fig. 9A ); they lack centrally positioned pores typical for the blumi-canadensis complex of species and Testechiniscus ( Gąsiorek et al., 2018) . In contrary to the original description ( Schuster and Grigarick, 1966), the species does not have dark red eye spots, which always dissolve in Hoyer’ s medium, but large black crystalline eyes identifiable in all examined paratypes ( Fig. 9B ). An erroneous ascribing of the red colour most probably resulted from a strong orange-reddish glow enclosing eyes. In fact, already the description in Schuster and Grigarick (1966) raised suspicions as the authors drew well-identifiable eyes in the mounted holotypic female, whereas red carotenoid eyes in echiniscids in the vast majority of cases vanish within an hour from preparing a permanent slide with a tardigrade. Echiniscus becki exhibits also a pair of exceptionally shaped subcephalic plates, which extend from the lateral portions of the head and twist in a boomerang-like manner at the level of pharynx ( Fig. 9B ).

Representatives of E. laterosetosus , collected in the high mountains of Honshu, allowed for providing the morphological details relevant to its taxonomy. Eye spots, drawn in the original description without stating their colour ( Ito, 1993), are small and black ( Fig. 10A ). The dorsal plate sculpturing consists of well-developed endocuticular pillars, each joined by striae with four or five neighbouring pillars, and pores distributed between them ( Fig. 10B ).

Figures

Fig. 9. Cephalic body portion of Echiniscus becki (PCM, paratype, female): A – dorsal view, B – ventral view (arrowheads indicate black crystalline eyes; large subcephalic plates visible as dark grey, broad belts bent in a boomerang-like shape). Scale bars = 10 μm.

Fig. 10. Habitus of Echiniscus laterosetosus (PCM, female): A – cephalic body portion with arrowheads pointing out black crystalline eyes, B – specimen in toto. Scale bars in μm.