Pholad Bivalve Borings

Recent pholad bivalve borings--rock boring clams
Some of the holes still had the clam shells in them

Locality: Just north of Kalaloch Campground
Jefferson County, Washington

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Pholad Bivalve Borings

These pictures were taken by Dr. Norm King
on his recent trip (November 2003) to the West coast.

Boring clams look for a place to live where no predators can get to them.

These particular types of Pholads (Family Pholadidae) bore by mechanical
abrasion. Members of other families use chemical means. Some bore into
wood, and are often called pile worms or ship worms, causing a great deal of
destruction to pilings in coastal regions.

They begin as tiny swimming juveniles that settle onto a rock or sediment or
wood surface. As they grow they move farther into the substrate, making a
larger boring except for the aperture. The aperture remains small--just
large enough for them to stick their siphon through. Since the body grows
but the opening stays the same size, they are trapped in their borings.

They pull in a current of water and filter out plankton. Most other clams
eat the same way, although a few have siphons (rubbery tubes) that literally
vacuum up food particles from the sea floor.

Norm King

Dr. Norm King's recent web publication

The I-170 Pennsylvanian Exposure in St. Louis, Missouri
This link takes you to a discussion by Dr. Norman R. King, Professor of
Geology at the University of Southern Indiana, about the rocks exposed
at the I-170 highway cut. Dr. King describes the rock units and correlates
them with rock units elsewhere in the Midcontinent region. He interprets
their environments of deposition, and also places them in the context of
larger-scale geological processes taking place in the Midcontinent region
and around the globe during the Pennsylvanian Period.

For those interested in reviewing Dr. King's publication, I suggest to
start by reading Genesis and Evolution of the I-170 Pennsylvanian Project
on the menu.

Barry Sutton

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