Puellina innominata is an encrusting bryozoan. Colonies form extensive, heavily calcified sheets, composed of a single layer of autozooids. Autozooids are broadly oval to irregularly polygonal, rather flat and separated by distinct grooves. They range in size from 0.29-0.51 by 0.18-0.30 mm. Five spines are present in non-reproductive zooids, and four in reproductive (with an ovicell) zooids.
The species is able to colonise shell and hard substrates. It has been recorded from the shallow subtidal zone to offshore waters (38-106 metres).
The long-standing taxonomic confusion surrounding this species was resolved by Bishop and Househam (1986). Puellina innominata has been recorded in error from almost every ocean, but its true distribution is almost certainly limited to the northeast Atlantic. In the British Isles, it is known from the English Channel, Sussex, Normandy, Brittany, Guernsey, Devon and Cornwall. It has also been recorded from Galway, off Antrim in the Irish Sea, off the west coast of Scotland and Shetland.