Twenty-eight species of Gastrotricha are listed in the order of an original systematic key to the known marine genera. The distribution of these species found during a survey of the interstitial fauna of some North Wales beaches is given. Records from an earlier survey by Dr B. Swedmark are included. Descriptions of three new species Paradasys cambriensis, Pleurodasys megasoma and Macrodasys remanei are given. All except one of the species recorded are believed new to the British Fauna List.