This study describes species of the genus Hymedesmia from three areas of cold-water coral reef: Mingulay Reef Complex (Scotland, UK) and Rockall and Porcupine Banks (off UK and Irish coasts). Five new species are described: Hymedesmia (Hymedesmia) gibbosa, H. stoneae, H. tendali, H. xavierae and H. valentinae. Records are provided of other poorly known Hymedesmia species: H. bocki, H. cohesibacilla, H. curvichela, H. ebria, H. gustafsoni, H. simillima, H. irregularis, H. proxima, H. hibernica and H. primitiva. Information on distribution of other Hymedesmia species occurring in Britain and Ireland is presented. The sites studied represent a variety of depth-ranges and the data collected suggest that some Hymedesmia species may be restricted to particular bathymetric zones.
