Nemoura avicularis

This proved quite challenging for me to ID and I'm really grateful to Jean-Paul G Reding for getting in touch and correcting my error. I had struggled when I examined it as at first the cerci hadn't looked like they had any hooks or points, but after rotating them to view from a different angle it then appeared that they had clear points on both sides. At this point I was leaning towards cinerea (the cerci of which have two chitinised points) but then I was unable to see anything in the abdomen that looked like the diagram in the key (Macadam, Feeley & Doe) for the epiproct for cinerea. My notes don't say why I ruled out avicularis at this point, but for some reason I thought if it wasn't cinerea it must be either cambrica or erratica. At first I didn't think the epiproct fitted these two either but eventually I realised that if I tilted the capsule I had extracted on one end I could see an arrangement that looked something like the diagrams in the book. It most closely matched the picture and description for cambrica, particularly with the sinuous twisted bits that I think are paraprocts, and for that reason I labelled it cambrica.

Jean-Paul G Reding got in touch to say that it is in fact Nemoura avicularis, referring to both my photos of the cercus and the genital capsule below, and noted that the latter shows the shape of the apical sclerite which is most reliable for identification. So I have now looked back at the key to see where I went wrong. I think my first mistake was probably in interpreting the shape of the cerci. On the opposite side to the hook on the cerci, the edge of the cercus is smoothly rounded, but because a section of this is membranous and almost transparent, it looks like it is indented. The easily visible sclerotised part of it has a point opposite the hook. The sharpness or roundedness of this point seems to vary according to the angle and I think it must have been this that initially gave me the impression that the cercus might have points on both sides and therefore be cinerea. I suspect that when I looked at the diagram of avicularis cercus and eliminated that as a possible ID, I had still not realised that the outline shape of the cerci was smoothly rounded opposite the point, not following the indented outline of the sclerotised part I could see more easily. In hindsight I observe that only avicularis is shown to have an eye-like feature just in from the apical curve of the cercus, and this is shown by my specimen. Had the key shown the epiprocts for avicularis as it does for cinerea, cambrica and erratica, perhaps I would have realised that mine matched avicularis and looked again at the cercus, but unfortunately this is omitted for avicularis. It explains why I had not found it easy to match the ectoprocts with any of the diagrams in the book.

male Nemoura avicularis showing cercus (4 orientations) and genital capsule (at 3 levels of tilting), Pensthorpe (Norfolk, UK), 15th May 2023

I had previously recorded female avicularis a couple of times but at that time I did not have sufficiently good equipment to photograph the relevant features, and I did not retain the specimens. They were also before the publication of Macadam, Feeley & Doe, and in view of the difficulties I've had with this genus subsequently I think it is probably wisest to consider my previous records as unproven.