Size is variable but always thin and mat-like, with a single lacy encrusting form with rectangular zooecia with a short pair of blunt horns projecting from the front corners. The edges of the colony are usually wavy. Colour is typically white to pale grey. Most commonly found on the fronds of large seaweeds

M. membranacea prefers shallow marine habitats between the mid intertidal to the shallow sublittoral. It may also be found in brackish water. M. membranacea has become an invasive species in many places, and is believed to have a potentially negative impact on marine ecosystems by limiting the ability of the seaweeds to reproduce.

Like other bryozoans, M. membranacea is a colonial organism that feeds on plankton extracted by the lophophore.