The genus contains a single species, B. leggi, and it was originally classified as the only member of its family, the Beornidae, but was later reclassified as belonging to the Hypsibiidae.

[1] The cuticle is smooth, and slightly thickened on the backside, but does not harden to platelets (sclerites), making Beorn is one of the "naked" tardigrades.

Other features, such as the structure of the stiletto apparatus or the mucous musculature, can not be recognized; Also the position of the sex opening (gonopore) with respect to the anus, which could have given further indications of the class belonging to the species, can not be ascertained.

Moreover, the species can even be assigned to one of the three modern classes - the absence of head structures such as cirri and clavae and back armoring suggests a placement within the Eutardigrada.

[7][4] To determine the relationships of Aerobius and Beorn, Mapalo, Wolfe & Ortega-Hernández (2024) phylogenetically analyzed a combination of morphological features and rRNA sequences.

These results are displayed in the cladogram below, with extinct species designated with a dagger (†):[4] Milnesium Eohypsibioidea Macrobiotoidea Ramajendas frigidus Isohypsibius prosostomus Halobiotus crispae Doryphoribius macrodon Hexapodibius micronyx †Paradoryphoribius Ramazzottius oberhaeuseri Microhypsibius truncatus Acutuncus antarcticus Calohypsibius ornatus Hypsibius dujardini †Beorn †Aerobius