Puellina modica is an encrusting bryozoan. Colonies form small, irregular patches, composed of a single layer of autozooids. The autozooids are broadly oval to hexagonal, convex and separated by deep grooves. They range in size from 0.17-0.25 by 0.08-0.12 mm. Five spines are present in non-reproductive zooids, and two in reproductive zooids (with an ovicell).
The species is able to colonise stones and shells. It has been recorded from offshore waters between 38-106 metres. Puellina modica is known from the English Channel off Sussex, Normandy, Brittany and Guernsey; from the Irish Sea and the Antrim coast.
Puellina modica may be distinguished from its close relatives, Puellina gattyae and Puellina setosa, by it prominent costal ridges.