The first full description of the Lochkovian acanthodian Euthacanthus gracilis, presented here, shows that the species shares many characters with the type species Euthacanthus macnicoli supporting its retention in this genus. Euthacanthus elegans is deemed to be a junior synonym of E. gracilis. E. gracilis differs from E. macnicoli in having large ‘umbellate’ scales edging the main lateral line canal, and small body scales. The crown morphology of the enlarged lateral line scales are similar to isolated ‘umbellate’ scales described world-wide in the Siluro-Devonian. They have the same general morphology as the sensory line scales on some other acanthodians including the sensory line scales on the head of Ischnacanthus gracilis and the lateral lines in Brochoadmones milesi. Neither of these articulated forms is closely related to Euthacanthus. The crown morphology of the normal flank scales is similar to that of the type species, and also the acritolepid acanthodian Acritolepis urvantsevi. Acritolepids are ischnacanthiform acanthodians, and are not closely related to Euthacanthus. This similarity indicates that scale crown morphology without histology is not always a useful tool in identifying species or genera from isolated remains.

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