Beania mirabilis is an inconspicuous encrusting bryozoan. Colonies are diffuse, ramifying over the substrate. They attach to the substrate by root-like rhizoids, growing from the basal surface at proximal end (closest to the colony origin) of an autozooid. The rhizoids terminate in a attachment disc. Autozooids are boat-shaped, contracted above and bulging below. They are suberect, with a free distal portion, and spines arranged along the outer edge. Typically 0.6-0.65 by 0.15 mm.
The species is able to colonise a range of substrate including shells and other Bryozoa e.g. Cellaria, Flustra and Pentapora. It is especially found on kelp (Laminaria) holdfasts. It ranges from the very lower intertidal down to 130 m.
This species is inconspicuous and therefore not often recorded. It is distributed from the Skaggerak and the British Isles, southwards through the Atlantic to the Indo-Pacific.