Clam-bored mudstone

Clam bored mudstone

Mudstone displaying boring clam traces.

Lithogenous sedimentary rock.
Greywacke mudstone displaying holes creadted by boring clams. Boring clams are any of several marine clams that bore into (abraiding the rock as the open and close while filter feeding). The out part of their shell has chitonous bristles that trap sand to abraid the rock, or they dissolve away rock, cement, clay, or mud, making chambers in which they live.
From Carlsbad beach, San Diego County, CA. 2/2/2021