Anyone know what this is?

My industrious 9 year old daughter Holly has found this while rooting around in the bathroom. Given her previous track record with co-finding Welsh firsts, I thought I'd better check this one out. I'm sure I recognise it from the past somewhere (Blastobasis sp?), but can't work out what it is. Perhaps at best 5mm long - I took the liberty of putting the end of a ruler in the photo.

Cheers
Mike Cram
(Bridgend)