Burrowing Bivalve, Pholadomya

These bivalves burrowed into the sand or mud of the seabed. The two valves are shortned at the front ( anterior end ) and show a conspicuous gape at the posterior. Through this opening the creature passed the siphons for respiration and feeding. The image below is a reconstruction of how the animal would have looked in life.

The creature seems to have secreted a mucous layer on the surface of the valves to trap gritty particles. This may have served like the knobbles on the shell of Trigonia to aid its burrowing in soft sand or could have acted like sandpaper to cut through soft rock. The image below is from another less well preserved specimen but it does show the gritty coating.