English: Fig 3. Comparison of phylogentically sister, complex non-burrowing Murmania antiqua (Martynov, 2006) (family Murmaniidae) from the Arctic Ocean with simplified facultative burrowing Xenocratena suecica Odhner, 1940 (family Xenocratenidae fam. n.) from the Atlantic (North Sea) waters of Sweden and Norway. The degree of simplification of ceratal (papillae-bearing) rows (every row is indicated by a separate arrow, majority of papillae were removed to clearly show the number of ceratal rows, which are counted according to the knob-like traces of the ceratal attachment on the dorsal side) can be evaluated directly between Xenocratena (A, B) and Murmania (D). Xenocratena (A, B) possesses no more than five (commonly fewer) of anterior ceratal rows and no more than eight (commonly fewer) ceratal rows in total. Murmania (D) possesses more than 20 anterior ceratal rows and more than 40 ceratal rows in total. Both small syntype (A, preserved specimen 4 mm in length) and newly discovered specimens (B, preserved, length 7 mm) specimens of Xenocratena suecica are compared with the large holotype specimen of Murmania antiqua (D, preserved, length 44 mm). The radular teeth of Xenocratena (C) and Murmania (E) are also presented to show the considerable morphological differences between these phylogenetically sister taxa. Abbreviations: c, cerata (dorsal papillae); ct, central teeth of radula; rn, rhinophores (chemical sense organs).