Puellina setosa is an encrusting bryozoan. Colonies form broad, spreading sheets, composed of a single layer of autozooids. Autozooids are broadly oval to irregularly polygonal. The proximal end of the autozooids is often tapered and occasionally bifid. They range in size from 0.20-0.42 by 0.14-0.27 mm. Five spines are present in non-reproductive zooids, and two in reproductive zooids (with an ovicell).
The species is able to colonise stones, shells and algae. It ranges from the shallow subtidal zone to offshore waters. Its distribution is incompletely known. It was originally described from Madeira and subsequently recorded from the Canary Isles, off the French Mediterranean coast, Naples and Greece. It does not seem to occur around the British Isles.