Seven species of marine algae in the Antithamnieae (Antithamnion lherminieri, An. decipiens) and Dohrnielleae sensu Athanasiadis (Callithamniella tingitana, Dohrniella antillara, Antithamnionella breviramosa, Aa graeffei, and a new species, Aa bermudica) are reported from the Bermuda islands for the first time. Taxonomic and nomenclatural problems with certain of these species collected in deep water are discussed. Aa bermudica sp. nov. has a prostrate, mat-forming habit and a unique branching pattern of whorl-branches for the genus. Its recurved whorl-branches are more reminiscent of certain species of Antithamnion, Perikladosporon and Pterothamnion, but gland cell ontogeny and position show the new species to be best placed in Antithamnionella.