Watersipora complanata is an encrusting bryozoan. Colonies form broad, white spreading sheets, which may be composed of a single or multiple layers of autozooids. Autozooids are oval to hexagonal and flat. They are 0.6-0.9 by 0.3-0.5 mm.
Watersipora complanata was originally described from an unknown British locality, but within the UK is currently only known from the Scilly Isles. It has also been reported from the Adriatic, Morocco and is widely distributed in the western Mediterranean
The species is able to colonise rocks, shells and the underside of stones on the lower shore.