Echiniscus spiniger Richters, 1904

Gąsiorek, Piotr & Degma, Peter, 2018, Three Echiniscidae species (Tardigrada: Heterotardigrada) new to the Polish fauna, with the description of a new gonochoristic Bryodelphax Thulin, 1928, Zootaxa 4410 (1), pp. 77-96 : 89-91

Echiniscus spiniger Richters, 1904

( Fig. 34 )

Locus typicus. Visby, Gotland, Sweden.

Material examined. Three adult specimens and one juvenile, found together with exceptionally abundant Echiniscus granulatus , E. testudo ( Doyère, 1840) , and Richtersius coronifer (PL.247; Kościeliska Valley.

Description. Medium-sized (160–313 µm), dark-yellow. Cirrus A long (104 µm, cirrus A/ body length ratio 33%). Cirrus internus / externus length ratio 60–65%. Plate sculpture composed of small and medium-sized pores ( spinulosus type), with the largest pores found on the large median plates and on the caudal plate. Lateral and dorsal appendages at B, C, C d, D, D d, and E in the shape of long spines, with dorsal spines slightly longer than the lateral ones (38–48 µm vs 21–36 µm). Pedal (leg) plates very well-developed and large, those on leg IV forming a collar composed of eight small, blunt teeth. Claws I–III moderately shorter than claws IV (12.5–20.6 µm, 27.3– 31.1% vs 16.9–23.6 µm, 30.3–38.3%). Spurs (1.5–3.9 µm, 3.4–5.8%) positioned at ~30% of the claw length.

Remarks. New record for Poland. Dastych (1988) expressed the opinion that the so-called spinulosus - quadrispinosus group was in need of a complete revision, and produced a schematic illustration of E. spinulosus ( Doyère, 1840) with long lateral appendages. He also remarked that the lateral appendages of Polish E. spinulosus specimens varied significantly in length ( Dastych 1988). Presented findings suggest that his records could embrace two distinct species: E. spinulosus s. s., which is a predominantly lowland species, and E. spiniger , more frequently found in colder and upland habitats. In E. spinulosus specimens from the locus typicus (Saint-Maur-des-Fossés, France), dorsal spines C d and D d are longer than the extremely short lateral spines (similar to the differences in length recorded for E. scabrospinosus Fontoura, 1982 , see Figs 31–32 ). In E. spiniger , the lateral spines are longer and of similar or equal development to the dorsal appendages ( Fig. 34 ).

Scottish specimens of E. quadrispinosus Richters, 1902 of identical body size to Polish E. spiniger specimens have dorsal spines C d and D d distinctly shorter than in E. spiniger , and unlike in E. spiniger , spines D d are typically shorter than C d ( Fig. 35 ). Moreover, all lateral appendages in E. quadrispinosus are developed as long cirri with broad bases ( Ramazzotti & Maucci 1983).

Pilato et al. (2008) showed that different species within spinulosus group can be separated on the basis of differences in plate sculpturing. An interesting pattern can be observed within members of the group: generally, species with short appendages exhibit large and sparsely distributed cuticular pores, whereas those with long spines or cirri possess comparatively smaller, more densely arranged pores (compare Figs 31–32 for E. spinulosus and E. scabrospinosus , and 33–35 for E. lichenorum Maucci, 1983 , E. spiniger and E. quadrispinosus ). Curiously, E. migiurtinus Franceschi, 1957 with reduced set of trunk appendages (exclusively stout spines D d present) seems to deviate from this rule, since it exhibits small, densely arranged pores ( Fig. 30 ). However, there are also differences in the degree of pedal (leg) plate development between the representatives of the spinulosus group. Such differences could be a stable specific trait. Pedal (leg) plates can be: invisible in PCM on all legs ( Fig. 32 ); visible only on legs IV ( Figs 30, 33, 35 , arrowheads); or present on all legs, and with strongly developed sculpture similar to that on the dorsal plates, which so far was detected only in E. spinulosus and E. spiniger ( Figs 31, 34 , arrowheads). It is clear that additional studies are needed to better understand the phylogeny and evolution of morphological traits within this species complex. For the Polish fauna, both E. spiniger and E. spinulosus should be considered as its indigenous components.

The presence of E. testudo , a typical lowland species, within this sample, represents the first record for this species from the Polish Tatras ( Dastych 1980).

Figures

FIGURES 30–35. Interspecific appendage length variability in the spinulosus group (PCM): 30—Echiniscus migiurtinus Franceschi, 1957 from Somalia (syntype), dorsal view; 31—Echiniscus spinulosus (Doyère, 1840) from France, lateral view; 32—Echiniscus scabrospinosus Fontoura, 1982 from Portugal, dorso-lateral view; 33—Echiniscus lichenorum Maucci, 1983 from Portugal, dorsal view (paratype); 34—Echiniscus spiniger Richters, 1904, a new addition to the Polish fauna, dorsolateral view; 35—Echiniscus quadrispinosus Richters, 1902 from Scotland, dorso-lateral view; arrowheads indicate pedal plates.Scale bars in µm.