Porella alba is an encrusting bryozoan that forms irregular spreading sheets, composed of a single layer of autozooids. Autozooids are small, oval to hexagonal and convex. They are 0.3-0.45 by about 0.2 mm.
Porella alba is an arctic-boreal species known from the Barents Sea, the White Sea, Sptizbergen and northern Iceland. In Britain, the species is reaching its extreme southern limit and only occurs rarely; it is known from a single specimen collected at Wick
The species is able to colonise a variety of substrates including stones, shells and kelp holdfasts. It ranges from the lower shore into shallow sublittoral waters.