Three new species and one re-description of Aka

Three new species of the boring genus Aka, A. coralliirubri, A. microterebrans and A. ruetzleri are described respectively from the Mediterranean Sea, Celebes Sea and Caribbean Sea. The Indo-Pacific A. maldiviensis, known only for the structure of its epilithic fistules, is here described in more detail. The new species confirm that the sponges comprising the genus Aka are able to bore in biogenic substrata only, in particular coral rock, bivalve shells and the scleraxis of the precious coral Corallium. The study of the macroscopic excavation shows that three different patterns can be described: producing discrete boring chambers, large undivided cavities and interconnecting microtunnels giving rise to a spongious aspect of the substratum.