Desoria violacea (formerly Isotoma violacea) is a common species with a distinctive dark violet-blue colouration. The long setae on the abdomen are relatively long, about the same length as (or slightly longer than) the fifth abdominal segment (Fig. 1). There are four teeth on the mucro (Fig. 2).
     It is possible that 'violacea' as understood here is a complex of two species, one that occurs in mountains and another more southern species. Desoria hiemalis is similar to Desoria violacea but the setae on the abdomen are much longer (2.0 to 2.3 times as long as abd5 according to Potapov (2001)). None of the specimens of Desoria violacea that I have seen have setae this long. Further taxonomic study is needed on fresh material to clarify the situation.

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Fig.2: Mucro with four teeth (*) of Desoria violacea collected from Long Churn Cave, Ribblesdale in April 1967 by the Cave Research Group.

Fig. 1: Dorsal side of Desoria violacea collected from Arch Cave, Fermanaughby in July 1966 by the Cave Research Group. The setae on the fifth abdominal segment (abd5) are about the same length as abd5.