The present work deals with twelve species of Sphaeromatidae from several substrata in the intertidal and shallow infralittoral zone in São Paulo and Rio de Janeiro States, Brazil. Sand, stones, empty tests of barnacles, empty tubes of polychaete, byssus of mussels, oyster beds, macroscopic algae and sea grass (Spartina alterniflora) were collected and analysed. The following nomenclatural changes have been made: Pseudosphaeroma jakobii and Exosphaeroma platense are synonymyzed with Cassidinidea tuberculata; Pseudosphaeroma rhombofrontalis is placed in the genus Tholozodium; Paradynoides brasiliensis antonii with D. tropica. A key to species, the geographical distribution and notes on the habitat of the species are also furnished.
