My wife and I took a walk around the estuary in Australind on the weekend and there were many hundreds of these collected in the grass and rocks along the shoreline. They have the shape of a water washed stone and the texture of a dreadlock. I’m not certain what the origins of them are. They do look very similar to Posidonia oceanica but they are found only in the Mediterranean Sea. Perhaps the regurgitated indigestible fibre of a sea grass matted in the belly of a sea creature?
I’ve put them on my coffee table for the puzzle. I hope a guest doesn’t try to eat one.