COLLEMBOLA > ENTOMOBRYOMORPHA > ENTOMOBRYOIDEA > Isotomidae > Isotominae

With this latest addition being the third species that I've managed to photograph from this family, it's useful to note that one of the important differences between isotomids and members of the Entomobryidae is that the body segments are of roughly equal length, whereas entomobryids are characterised by having an enlarged fourth abdominal segment.

I'd previously noted that the Isotomidae family comprises a large number of species in many genera. I believe that the most frequently observed species are from the Isotominae subfamily, within either Isotoma, Isotomurus, Desoria or Vertagopus. The presence and positioning of body hairs (setae), particularly any long hairs (macrosetae) are very useful distinguishing features especially when it comes to separating the two genera currently represented here. There are other defining characters such as the number of teeth on the mucro (the tip of the furca) and the arrangement of the ocelli, but those details are very rarely visible in photos, so the presence of any long setae is extremely helpful. In Isotoma it typically covers all body segments, but in Isotomurus species it is confined to the rear end (abd4-6) as can be clearly seen here.

I mentioned on the previous account that Isotomurus pseudopalustris was one of the species that had traditionally been lumped together with other variants under what had been known as the 'palustris group'. These species are now separated. Adults have characteristic pigmentation patterns that certainly helps with identification but, even so, the genus can be challenging. In many cases the advice is simply to record as Isotomurus palustris sensu lato unless there is sufficient detail to suggest an actual species. Isotomurus pseudopalustris isn't included in the original 'key' but it is mentioned with the suggestion that it may even be the same species as Isotomurus unifasciatus (see previous page). I believe that thinking has now been pushed to one side as it is now considered a species in its own right. It has a dark broken mid-line with two characteristic, although often hard to distinguish, pale marks either side on abd4 and some pigmentation on the sides.