Populations of Diaperoforma californica (d'Orbigny) bryoliths were discovered in rhodolith beds, a sand habitat, and on a cobble bottom in the Gulf of California, Mexico, the first known observation of a modern free-living cyclostome bryozoan in the Northern Hemisphere. Densities ranged from a mean of 9.2 to 22.6 individuals/0.06 m². Bryoliths from the deepest site were irregularly shaped and had the highest variation in shape; those from shallow sites were spheroidal. Water motion and bioturbation move the bryoliths and may determine their morphology. Schizomavella robertsonae (Soule, Soule & Chaney) bryoliths also occurred occasionally in one rhodolith bed sampled. Fossilized bryolith specimens of the cyclostome Diaperoforma californica (d'Orbigny) were found in a Pleistocene deposit near modern habitats.