Small specimen of a little known brachiopod found mainly in S. CA but also described as far north as Tomales Bay. It has turned up in a few recent surveys in Elkhorn Slough. ID and info from John Pearse and Mark Silberstein.
I was always told these were brachiopods
Highlands Intermediate CoastBlitz Tapuae
Often you can see vein like patterns through the outside of these shells. They are quite robust in the sense that they easily seem to stay whole.
At Elkhorn Slough National Estuarine Research Reserve
Brachiopods, phylum Brachiopoda, are marine animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, while the front can be opened for feeding or closed for protection. Two major groups are recognized, articulate and inarticulate. Articulate brachiopods have toothed hinges and simple opening and closing muscles, while inarticulate brachiopods have untoothed hinges and a more complex system...