Species of Mesaphorura are very small (typically 0.7 mm in length) soil-dwelling Collembola. Until relatively recently, most Mesaphorura have been recorded under the name Mesaphorura krausbaueri but following work by Rusek and others, it is clear that there are several species 'hiding' under this name. Indeed, most of the slides in the NHML collection labelled 'Mesaphorura krausbaueri' are in fact Mesaphorura macrochaeta. The literature records suggest that Mesaphorura krausbaueri is a common and widespread species but the map exhibits a much more scattered distribution than Mesaphorura macrochaeta. There are too few records to give an opinion on the true distribution of Mesaphorura krausbaueri. Most of the literature records (green dots) shown on the map should be regarded as Mesaphorura sp. pending examination of specimens from the same localities.
     The pseudocelli formula of Mesaphorura krausbaueri is 11/011/10011. Other diagnostic characters include five setae in tibiotarsal 'B' ring, seta a2 present on th3, distance between p1 setae on abd4 shorter than the distance between the p2 setae, seta m0 on abd4 absent, 3+3 short setae on abd5 between the long a4 setae, and anal setae l2' absent (Figs. 1 and 2; this latter character is the only discernible difference from Mesaphorura macrochaeta in which anal setae l2' are present - the legitimacy of using this character might be questioned but it is reasonably easy to see in most specimens if they have been cleared and orientated appropriately).

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Fig. 1 (above): Anus of Mesaphorura krausbaueri collected from Ruislip, Middlesex in January 1951 by J.T. Salmon. The setae are numbered after Fig. 156 in Arne Fjellberg's (1980) key to Norwegian Collembola. Note that the pair of setae l2' are absent.

Fig. 2 (above): Anus of Mesaphorura krausbaueri collected from Parliament Hill Fields, London in December 1952 by D.S. Murphy. For setal numbering, compare this photograph with Fig. 1. Note the absence of the pair of setae l2' (*).