An abundant population of the sea pen Cavernularia pusilla (Anthozoa: Pennatulacea), with up to 70 colonies m−2, has been found on soft bottoms off the Basque coast (south-east Bay of Biscay, north-east Atlantic). This species spreads in an area of several kilometres length, and its bathymetric distribution ranges between 35 and 85 m depth, reaching its highest densities at 45–55 m. Such a population is remarkable, considering the scarce available records of this species and its southern affinities. The geographic and bathymetric distributions of the species are revised and discussed.
