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Not familiar to this species, but very angular front of head is noticeably different to S.expinosus & S.vetulus. Nice photo. Any close ups of head?
I think a close-up showing the spinules on the head are beyond my camera/microscope combination, but I'll have a go.
There aren't many records of this species in Britain, but it has been found several times on Anglesey, first by Scourfield over a century ago.
I've had a go at photographing the head spinules - two more photos added. The one at x400 has come out reasonably well, enough to prove they exist.
Lat/Lng: 53.2159, -4.3481
OS grid ref: SH433713