(299.5ISrip) Isotoma riparia (Nicolet, 1842)

Isotoma riparia (Fig. 1) is a scarce species confined to very wet sites. The morphological characters are similar to Isotoma viridis (three teeth on the mucro) although the lateral teeth on the claws are more strongly developed in Isotoma riparia. The most characteristic feature is a strong central stripe on the body (Fig. 1) which gives this species a superficial resemblance to an Isotomurus without the trichobothria.
Peter Shaw discovered several specimens of Isotoma riparia associated with an ash lagoon at West Thurrock on the Thames Estuary in September 2000. However, there are two specimens (on the same slide) in the NHML collection found in 1963 by Peter Lawrence in a salt marsh in Dorset (Fig. 1). These are labelled 'Isotoma viridis' but have a very clear central stripe and agree with Potapov's (2001) description of Isotoma riparia.  Around 2005 Steve Hopkin found this species in flood debris on the banks of the River Thames near Reading.  This species is probably greatly under-recorded.




Fig. 1: Isotoma riparia of 2.1 mm in length collected from the edge of a salt marsh at Hartland Moor in November 1963 by Peter Lawrence.

Fig. 2: Isotoma riparia of 2.0 mm in length collected from flood debris on the banks of the River Thames near Reading. The specimen bears a superficial resemblance to Isotomurus plumosus but lacks trichobothria on the dorsal side of the abdomen.

Isotoma riparia 2mm from West Thurrock PFA lagoon, Essex, June 1998

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