This epiphytic bryozoan forms encrusting lacy mat-like colonies of very small, rectangular autozooids, 0.42 x 0.13 mm, with tubercules or short spines in the corners. Each zooid has lateral calcified walls that contain ventral uncalcified bands providing flexibility. A frontal membrane completely roofs the space between the supporting side walls with a lophophore (feeding tentacles) visible within. Tower zooids may also be present; where the frontal membrane projects upwards in a columnar way.Colonies may vary in size. Membranipora membranacea
grows quickly (several mm/day) in response to predation from sea slugs and in order to maintain its position on the kelp frond. Prolific growth is favoured by fast flowing water which provides food and oxygen. Egg production occurs once a year in the spring; the larva (cyphonautes) is planktotrophic and is the most abundant and largest coastal larva in Britain between June and August. The larva settles in late summer-early autumn.