Umbonula ovicellata is an encrusting bryozoan. Autozooids are oval to hexagonal and strongly convex. They range in size from 0.56-0.78 by 0.36-0.5 mm.
Umbonula ovicellata is widely distributed in the Mediterranean, reaching its northern limit in south-west Britain. It has been reported from the Channel Islands, the coasts of Cornwall, Devon and Dorset and as far east as Swanage, but does not seem to reach Lundy or south-west Wales.
The species is able to colonise red and brown algae, Posidonia seagrass, Laminaria holdfasts, other Bryozoa such as Crisia and Pentapora and hard substrates. In Britain the species is strictly subtidal distinguishing it from Oshurkovia littoralis with which it was formerly confused. In the Mediterranean, U. ovicellata ranges from 0-50 m.