Snake Millipede Proteroiulus fuscus

Apparently a very common species but there are some other members of the family Blaniulidae are very similar. The other species have a single row of ocelli whereas this one often has the start of a second row (just one or two ocelli in the second row) so that the black patch surrounding the ocelli is narrowly triangular.

On this specimen it was easy to see that the black field of ocelli was narrowly triangular, but I struggled to make out the individual ocelli in the second row. I was pretty sure I could see at least one, but not 100% sure (it's actually clearer in the photo below than it was just looking down the microscope). Young fuscus that have just a single row of ocelli can be distinguished from the similar Choneiulus palmatus by the number of setae fringing the metazonites (fewer than 10 on fuscus or more on palmatus) and this seemed to have slightly more than 10 - but it wasn't clear from the key whether this character was relevant for adults or not, so I needed to resolve for certain whether or not there was the start of a second row of ocelli. To do this I cleared it in potassium hydroxide and this made it much easier to see the individual ocelli, and this enabled me to confirm the presence of two ocelli in a second row.

Snake Millipede Proteroiulus fuscus showing ocelli (fresh and cleared), Dillington Carr (Norfolk, UK), 28th March 2022