Arctodiphascon, Tumanov & Tsvetkova, 2023

Genus Arctodiphascon gen. nov.

Type species: Diphascon tenue Thulin, 1928

Diagnosis. Peribuccal structures consisted of six peribuccal lobes. AISM in shape of “semilunar hooks” asymmetrical with respect to frontal plane with dorsal apophyses being distinctly higher, shorter and thicker than ventral ones, caudal processes of both apophyses pointing posteriorly and laterally. Buccal tube followed by a flexible annulated pharyngeal tube, with drop-like apodeme, bearing annulation between them. Pharynx oval with three bar-like, elongate macroplacoids. Microplacoids or septula absent. Claws of Hypsibius - type. Lunules and cuticular bars on limbs absent. Eggs laid within exuviae, with numerous minute pillars-like processes on chorion surface .

Comparison. Arctodiphascon gen. nov. is most similar to Bindius ( Pilato, 2009) in having an asymmetrical AISM, a long thin bucco-pharyngeal tube and three rod-like macroplacoids, but differs clearly from the latter in having the drop-like apodeme of the bucco-pharyngeal tube, which is completely absent in Bindius . Arctodiphascon gen. nov. is also similar to Guidettion in having a long thin bucco-pharyngeal tube and three rod-like macroplacoids without microplacoids or septula, but differs clearly from it in having a drop-like apodeme of the bucco-pharyngeal tube and an asymmetrical AISM. Arctodiphascon gen. nov. is similar to Diphascon in having a drop-like apodeme of the bucco-pharyngeal tube and three macroplacoids, but clearly differs from it in having no microplacoid or septula. The only species lacking both microplacoids and septula currently assigned to Diphascon is D. speciosum (Mihelčič, 1971) (nomen dubium according to Dastych, 2015), but this species has a granulated body cuticle, while the body surface in Arctodiphascon gen. nov. lacks granulation.

Note. The establishment of Arctodiphascon gen. nov. is substantiated by the morphological and molecular phylogenetic analysis presented below.

Etymology. The name refers to the morphological similarity of the new genus to the genus Diphascon , and to the predominantly arctic distribution of its type species Arctodiphascon tenue , comb. nov.

Genus composition (two species): Arctodiphascon tenue ( Thulin, 1928) , comb. nov. and A. wuyingensis ( Sun, Zhang, Wang, Zhao et Luo, 2020) , comb. nov. (placed tentatively; for the position of A. wuyingensis , see discussion below).