Failed rescue attempt

For a few days, I hosted a pair of small clams that I found abandoned high and dry on the beach, probably dropped by gulls, then left because they didn't break. The treatment had been too much for them, though; they didn't survive.

But they tried their best. Here's one, showing his teeth.

With a hermit almost small enough to enter that tunnel.

A clam has two siphons, which it extends up to the top of the sand to feed. (This clam did not burrow into the sand, a sign that it wasn't feeling all that well.) Water enters through the one towards the front, away from the hinge, (the incurrent siphon), food and oxygen are filtered out, and the waste water is pumped out through the rear siphon (excurrent).

Since the clam is a filter feeder, straining out microplankton and organic "dust" from the water, the hermit crab is in no danger; he's not going to be sucked in by the gentle current the clam generates.

Nor will he be bitten by those "teeth" around the opening of the siphon.

I couldn't find a name or a function for these tooth-like structures.