COLLEMBOLA > SYMPHYPLEONA > Dicyrtomidae > Ptenothricinae

Although I originally said that this particular species could be effectively ignored due to its rarity, I managed to find one, albeit by accident as I initially thought it was Dicyrtoma fusca. Fortunately, though, it was identified by someone on the UK Collembola FB Group who had knowledge of the species, and from where it transpired that, although still very scarce, it's not quite as rare as it used to be.

When the late Steve Hopkin's 'key' was first published in 2007, Ptenothrix atra was definitely extremely rare as there was only a single confirmed record, which dated back to 1943. In fact, even today that seems to be the case as there's still very little information about the species and certainly no up-to-date description confirming even basic details such as colour or general body form.

The original 'key' confirmed that, as with all species of the Dicyrtomidae family, they have a very short fourth antennal segment in addition to a, presumably characteristic, subdivided third segment. The member of the FB Group who identified the specimen shown below also noted that the pale tips to the antennae were another good identification feature. The spines on the abdomen are relatively long, more so than in Dicyrtoma fusca, and the dorsal surface of the rear end (abd6) bears long erect setae that point vertically upwards as opposed to the shorter setae found in Dicyrtoma fusca that lay back at an angle. In terms of size, Ptenothrix atra is slightly larger reaching a maximum length of 2.7mm compared with 2mm.

I've submitted a couple of photos in an attempt to get an official confirmation, but I'm pretty sure that it won't be accepted as a record, simply because the specimen would have to have been retained for proper examination of the claw on the foot to check that it's not wrapped in an outer membrane and that the empodium bears a long filament, and that both the inner and outer edges of the mucro (the end segment of the tiny furcula) are serrated - details that can only be seen under a microscope.

This particular individual was found in woodland under a large log.