Isotoma antennalis is a scarce species. The only confirmed records are from mountainous acidic sites. A record from Kew Gardens seems unlikely and needs confirmation. Isotoma antennalis is blue-black in colour. It is morphologically similar to species of Isotomurus but does not have trichobothria on the body. A decision to transfer the species from Isotoma to Isotomurus was made by Potapov (2001). He considered that antennalis 'obviously belongs to the genus Isotomurus in having a characteristic mucro, numerous and short setae on the body, many setae on the labium and on the posterior side of the dens'. However, I have decided to retain this species in Isotoma for the moment, at least for the purposes of identification in the AIDGAP key. The maximum length is 3.0 mm

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Fig. 1 : Mucro of Isotoma antennalis collected from Blanchland Moor (600 m) in June 1939 by Bagnall. There are four teeth on the mucro (*). The apical tooth (arrow) is small and the whole mucro is 'Isotomurus-like' and quite long.