Smittoidea amplissima is an encrusting bryozoan that forms broad sheets. Autozooids are oval to quadrate and approximately 0.6-0.8 by 0.4 mm.
The species is little known and was formerly confused with both Smittina landsborovii and Smittoidea reticulata. Its distribution is therefore uncertain. It appears to be found in the south and west of the British Isles, having been recorded from Guernsey, the Scilly Isles, Lough Hyne and the coast of Galway. Outside of the UK, it has been reported from Ferrol Ria in Galicia.
The species is able to colonise hard substrates in offshore habitats