Porella concinna is an encrusting bryozoan that forms extensive spreading sheets, composed of a single layer of autozooids. Colonies are reddish in colour. Autozooids are oval to hexagonal, or with an irregular outline. They are 0.4-0.5 by 0.25-0.4 mm.
Porella concinna is common off all British coasts. It ranges from the western Mediterranean to the Faroe Isles and western Norway. It distribution in Arctic waters needs to be re-examined as boreal and Arctic species of Porella are poorly known.
The species is able to colonise stones, shells and other organic carbonates in offshore habitats.