Cribrilina cryptooecium is an encrusting bryozoan. Colonies form irregular patches that often become extensive. The autozooids are small oval and convex. They range in size from 0.32-0.56 by 0.22-0.35 mm. Two short, thick spines are present in reproductive autozooids. Cribrilina cryptooecium shows a variable degree of calcification which may profoundly affect the appearance of the colony.
The species is able to colonise shells and especially the underside of stones where it is often abundant. It is also able to colonise algal substrates such as Fucus serratus. It is common on British shores and extends into shallow subtidal waters.
Cribrilina cryptooecium is distributed in the temperate waters of the northeast Atlantic, extending from Arctic Russia south to Guernsey. It has been recorded in the Barents Sea, Bergen Fjord, Shetland, the west coast of Ireland, the Irish Sea, south-west England, Guernsey and the North Sea coast of northern England. It also occurs on the coasts of eastern Canada and the northeast United States.