Abstract
The Galeommatoidea are a diverse but little-studied group of small bivalves, well known for the symbiotic relationships many species have with a range of invertebrate taxa. Four species collected from the Western Cape region of South Africa were examined and illustrated, providing new details on their habitat preferences, and depicting the mantle structure of live specimens for the first time. Brachiomyaducentiunus sp. nov., is described herein, and an additional record of Montacutasubstriata (Montagu, 1808) is reported from South Africa. Brachiomyaducentiunus and Montacutasubstriata have obligate symbiotic relationships with different burrowing echinoids, while Kelliabecki (WH Turton, 1932) and Melliteryxmactroides (Hanley, 1857) are free-living. DNA data and phylogenetic analyses are provided for three of the species.