Testechiniscus (Kristensen, 1987)

Gąsiorek, Piotr, 2023, Eventually tested: Phylogenetic position of “ Testechiniscus ” meridionalis (Murray, 1906) (Heterotardigrada) revealed, Zoologischer Anzeiger 304, pp. 49-60 : 57-58

4.2. Re-defining Testechiniscus and the composition of Diploechiniscus

At present, the definition of Testechiniscus stands as follows: “Medium-sized echiniscids with black, crystalline eyes. Rigid buccal tube with large cuticular stylet supports. Appendaged, i.e. having both cephalic and trunk cirri. Two pairs of segmental plates, unpaired scapular and caudal plates. Three median plates. Cuticular sculpture composed of large true round or polygonal pores that gradually become reticulum. Incisions (notches) on caudal (terminal) plate. Eight rows of ventral plates. No pseudosegmental plates.” ( Gąsiorek et al., 2018). I would like to add a new character to the diagnosis: the presence of dorsolateral spicules. This trait is an advanced convergence of Diploechiniscus and Testechiniscus , absent in all but three species of Echiniscus : E. laterosetosus , E. polygonalis ( Ito, 1993; it is worth noting that both are similar and potentially conspecific), and E. tympanista ( Murray, 1911; a species of incomplete description and never found again). Given that eyes of E. laterosetosus are black and crystalline ( Fig. 10A ; eyes were reported as “present” in Ito, 1993, and drawn in black therein), the dorsal sculpturing comprises densely arranged endocuticular pillars intermingled with pores ( Fig. 10B ), and the abovementioned dorsolateral spicules are present in the positions Bl, Cl, Dl, and El, I transfer both E. laterosetosus and E. polygonalis to Diploechiniscus as D. laterosetosus ( Ito, 1993) comb. nov. and D. polygonalis ( Ito, 1993) comb. nov., pending further tests of the probable conspecificity. Such action agrees also with the biogeography of the genus, which is a Holarctic taxon ( Vicente et al., 2013).

By adding such a character to the diagnosis, Testechiniscus becomes truly separate from both Diploechiniscus and Echiniscus ( E. tympanista is probably related to Diploechiniscus oihonnae , as noted by Murray (1911) himself). The next step is the removal of “ Testechiniscus ” macronyx from Testechiniscus , which should be performed with the application of integrative approach by precisely determining its place in the echiniscid evolutionary tree. Its autapomorphies ( Gąsiorek et al., 2018) make it unclassifiable within either Diploechiniscus , Echiniscus , or Testechiniscus .

Figures

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.