Porella struma is an encrusting bryozoan that develops brittle, spreading sheets, composed of a single layer of autozooids. Colonies are yellowish in colour and develop frilled expansions, with parts of the colony becoming free of the substratum on occasion. Autozooids are large and flat. They are quadrangular to hexagonal or with an irregular outline.
Porella struma is a boreal-arctic species that is distributed in the NE Atlantic south to western Norway, Faroe and Shetland.
The species is able to colonise hard substrates in offshore habitats.