Agrenia bidenticulata is a common species found in wet habitats in northern England, North Wales, Scotland and Ireland. It is frequently found submerged under stones in mountain streams (and sometimes in caves). The body is greenish in colour, the PAO is small and almost circular and the eyes each have eight ocelli. The biggest specimen Steve Hopkin measured (from the Devil's Kitchen in North Wales) was 2.3 mm in length. The basal part of the claw is wrapped in a membrane (Fig. 1) and the dens has a long spine reaching well beyond the end of the mucro (Fig. 2).