#pholadidae

AKA Parapholas janellii, Pholas californica, and Pholas janellii.

A rock-boring clam found in shale, mudstone, chert and hard sand along the Pacific coast of North America. They line the tunnel with a chimney made of small rock fragments glued together with calcium carbonate, and the chimney may protrude a short way into the water column.

AKA Angelwings.

As the sign under the fossil says, not every shell in the cliffs along the fossil coast are actually fossils, although some have certainly been there a good while, because they dug their way into the soft rock before the entire area got pushed back up above sealevel.

Pholadidea and the other genera in the family twist their shells back and forth to excavate tubular burrows in clay, peat or soft rock. Despite the hard work involved, the shells are actually quite fragile, and difficult to collect intact. Pholas dactylus, the common piddock, can not only manage the same trick in harder rock, but is also bioluminescent.

The fragile and beautiful rock-boring mollusc Barnea australasiae, or Australian Angelwing

A common species, found all around Australia’s coasts, where they use their ridged shells to bore into hard clay and soft rock. Curiously enough, the shells are also so fragile that they’re rarely found intact, once they’re removed from their burrow. After they eventually die, the burrow is used by other animals.

Angelwings and Piddocks form the family Pholadidae. Some species are known to live for at least 8 years, and the common piddock is not only bioluminescent, it’s hardcore enough to bore into gneiss. There’s a link on the wiki to a 1905 issue of the Field Naturalists' Club of Victoria journal, that makes the strange claim that eating Pholas helped earn the first Scots king his throne. Annoyingly, it provides no other info, or a source for the claim, and I’ve found nothing like it on Google.