Parapholas californica (Conrad 1837)

We find numerous siphons of these boring clams in the shale beds off Del Monte Beach. It has never been determined how the clams manage to bore into rock such as chert that is much harder than their shells. Depth 13 m.

Divers commonly find the siphons of these boring clams in shale beds. This individual has been extracted from its shale home. The boring end has a sharp, abrading sculpture.

scale-sided piddock clam

The anterior end of the shell gapes widely to give room for the foot to extend. This view shows the shell of an individual in place in a broken piece of shale. I turned the broken rock over so the interior end of the burrow is exposed. A burrow of a neighboring individual can be seen below, and the shell of another neighbor appears to the right. Note the large myophores (apophyses), to which the foot anchors, inside the shell. The burrow becomes more narrow toward the entrance, which cannot be seen here but is down and to the right. If this individual were fully mature a calcareous callum would have grown over the large anterior gape which is visible here.

Here is another view of the inside of the shell, showing the rounded hinge, the large myophore (apophysis), and the protoplax anterior of the hinge.

In this view, the rock has broken off at the very interior end of the hole so the position of the shell while boring can be seen. The anterior teeth are used for boring. The sinuous flap on the dorsal side of the shell is the protoplax.

Here is another view of the anterior end, with the protoplax downward. Scale is millimeters (centimeters numbered).

This lateral and dorsal view of the right valve shows how the anterior (left in the photo) end is inflated relative to the posterior (right in the photo) end. The protoplax can be seen along the dorsal (lower left) edge of the anterior end, and the metaplax can be seen along the dorsal (lower right) edge posterior to the umbo.

The posterior end of the shell has the periostracum formed into distinctive, overlapping chitinous plates. Note that the posterior end is narrower than the anterior.

Shell of an immature Parapholas californica found in broken shale near Santa Barbara, CA. The anterior, boring end is downward in this view. Note the large myophore inside the shell near the hinge. (Photo by: Dave Cowles, January 1996)