Cornechiniscus holmeni

3.4. Updated description of Cornechiniscus holmeni (Petersen, 1951)

Figs. 7D and 12–16, Tables 6–8.

3.4.1. Type locality

82 Ǫ 12 ′ N, 31 Ǫ 30 ′ W, 75 m asl: North Greenland, Peary Land, Brønlund Fjord.

3.4.2. New material

46 Ǫ 30 ′ 29 ′′ N, 11 Ǫ 49 ′ 41 ′′ E, ca. 3000 m asl: Italy, Province of Trento, Dolomites, Piz Bo`e. 15 adult females, 14 juveniles and 18 larvae on slides IT.339.06–25. All larvae hatched from eggs deposited in four exuvia that were maintained on a glass cube in a laboratory. 12 females on SEM stub no. 20.11. Five hologenophores preserved on slide IT.339.01. Found together with Echiniscus granulatus (Doy`ere, 1840), Diaforobiotus hyperonyx (Maucci, 1982), and members of Pseudechiniscus and Richtersius that will be addressed in future studies. All deposited in the Department of Invertebrate Evolution of the Jagiellonian University.

3.4.3. Adult females (i.e. from the third instar onwards; measurements and statistics in Table 6)

Body dark orange to red, massive (Figs. 12 and 13). Spines E can be doubled (Fig. 12), or elongated as far as they resemble filamentous cirri (Fig. 14A). Dorsal sculpturing consists of epicuticular granules with a surrounding ring of thin wrinkles (Fig. 15A), the latter imperceptible in PCM (Fig. 14A). Large and robust spine I and tooth IV (Figs. 12–14A, 15B). Claws strongly heteronych and robust (Fig. 15B and C, 16).

3.4.4. Juveniles (i.e. the second instar; measurements and statistics in Table 7)

Dorsal spiniform appendages can be particularly massive (Fig. 14B). Smaller than adult females.

3.4.5. Larvae (i.e. the first instar; measurements and statistics in Table 8)

All trunk appendages formed as in older life stages (Fig. 14C). Larvae were pale yellow alive, crawling vigorously in a caterpillar-like manner.

3.4.6. DNA sequences Single haplotypes were obtained in all four markers (Table 2).

3.4.7. Comparison between populations from the Holarctic and concluding remarks

The species has preferences towards polar/high mountain habitats in the Holarctic (Jørgensen and Kristensen, 1991; Gąsiorek and Michalczyk, 2020), what inclined Maucci (1982) to hypothesise that it is a tardigrade postglacial relic. When examining specimens originating from Caucasus, Dastych (1979b) concluded that slight disparities in the dorsal sculpturing between the population from Axel Heiberg Island (Canadian Arctic; Węglarska and Kuc, 1980) and Western Palaearctic representatives, and sporadic spurs directed upwards found in the Caucasus population, could warrant dividing C. holmeni into subspecies. Although the level of inter-population diversification remains to be investigated with the application of molecular techniques in this case, a relatively low genetic diversity has already been demonstrated for a member of the genus Cryoconicus inhabiting Central Asian glaciers (Zawierucha et al., 2018), which is consistent with other widely distributed tardigrade species (Jørgensen et al., 2007; Gąsiorek et al., 2019a). Consequently, it could be expected that C. holmeni is another tardigrade stenothermic species with poorly differentiated genetic structure. Irrespectively of the factual genetic diversity within the species, its morphological variability does not deviate from that of an average echiniscid (e.g. Gąsiorek et al., 2019b). Two other Cornechiniscus species, C. lobatus and C. madagascariensis, for which at least two populations originating from distant locales were shown as conspecific, exhibit comparably minor dorsal plate sculpturing variability (Maucci, 1993; Abe and Takeda, 2000; Gąsiorek and Michalczyk, 2020). This would mean that the differences in the size of granules and development of striae caught by Dastych (1979b) constitute a significant intraspecific variation as for the genus. Both Dastych (1979b) and Beasley and Miller (2007) collated the dorsal ornamentation of C. holmeni with that of the Echiniscus blumi-canadensis complex, suggesting their similarity. In fact, epicuticular granules of C. holmeni fall within the morphotype variability known for the genus (Gąsiorek and Michalczyk, 2020), and do not resemble large pores with thick polygonal edges typical for e.g. E. blumi Richters, 1903, but rather sculpturing described in E. weisseri from Afghanistan (Maucci, 1978). To summarise, recorded populations of C. holmeni form a morphological continuum and most probably are an evidence of relictual character of this species, which means a low dispersal potential.