On the systematic position of the genus Fractonotus (Eutardigrada, Parachela)

Abstract

The genus Fractonotus was erected on the basis of the peculiar appearance of the apophyses for the insertion of the stylet muscles on the buccal tube, and it has been attributed, together with the genus Microhypsibius, to the family Microhypsibiidae on the basis of the structure of the claws. A subsequent molecular investigation on Microhypsibius (18S and 28S rRNA) assigned the family Microhypsibiidae to the superfamily Hypsibioidea. Recently two other species, Isohypsibius gilvus and Calohypsibius verrucosus were transferred to Fractonotus and the latter was sequenced (18S and 28S rDNA, ITS-2), with the conclusion that the genus Fractonotus should be assigned to the family Isohypsibiidae, superfamily Isohypsibioidea. However, the transfer of I. gilvus and C. verrucosus to Fractonotus was incorrect. In fact, these two species definitely have claws of the Isohypsibius type, while Fractonotus caelatus, the type species of the genus, clearly has claws of the Microhypsibius type, in addition to other characters of the Hypsibioidea. Therefore, Fractonotus remains a monospecific genus in the Microhypsibiidae family, superfamily Hypsibioidea. The other two species belong to Isohypsibius or, if later confirmed by further morphological and new molecular data, to a new genus of Isohypsibiidae.

Keywords

• Tardigrada
• Fractonotus
• systematic position
• Hypsibioidea
• Isohypsibioidea