Good photos, matto.
They look quite regularly spaced as if one goes to each rib which makes me think they are nerves.
Maybe its just cos they were so skinny from some other reason that you could see them clearly this time.
Perhaps been chased by pig dogs to a less favourable habitat like south of the bridge.
Intersting suggestion, @
Tahr . Sounds like those are established in NZ. I wonder what is the snail host here ? Perhaps they are more numerous in Pureora due to long term rat / possum control. But I still dont think these particular ones were worms.