Smittoidea marmorea is an encrusting bryozoan. Autozooids are quadrate to hexagonal and flat. They are 0.4-0.5 by 0.25-0.3 mm.
Smittoidea marmorea is a warm temperate species that is widespread in the Mediterranean. In British waters is occurs along southern and western coasts, from the Channel Islands to Shetland.
The species is able to colonise stones and shells. It occurs in subtidal waters from below the kelp zone onto the continental shelf.