Eophliantidae are poorly studied marine algal-dwelling amphipods with a wide distribution. A new species was found to excavate burrows across the main stem of Carpophyllum maschalocarpum (Turner) Grev. in the New Zealand subtidal, and a detailed morphological description of this amphipod is given. Bircenna macayai sp. nov. can be distinguished from other Bircenna species by a combination of the following characters: bilobed coxa 1, merus and carpus of pereopods 5–7 strongly extended posteriorly, crenulate basis of pereopod 7 and smooth posterior margin of epimeron 3, pereopod 7 basis longer than wide. A key to the fourteen world species of Eophliantidae is provided. Taxonomy, evolutionary sequences, functional morphology and biogeography of the Eophliantidae are briefly discussed. New Zealand and Australian shallow waters show the highest species diversity of Eophliantidae, containing both species bearing plesiomorphic and highly derived characters, suggesting that Australasia is an evolutionary centre for this amphipod family.
