Hard Clam

Mercenaria mercenaria

The hard clam is a bivalve mollusk with thick, ridged shells that vary in color from brownish to grayish or white.

• Shells are egg- or heart-shaped.
• The interior of the shells is usually white with dark purple patches.
• The shells, or valves, are joined at the hinge by a thick brown external ligament.
• A hatchet-shaped foot and two short siphons periodically extend from the clam's soft interior.
• Can grow to about 4 inches.

Where does the hard clam live?

Hard clams use their foot to bury themselves in sand or muddy sand from the intertidal zone to depths of about 60 feet.

• The bulk of the Bay's hard clams are located in Virginia waters.
• In the Maryland portion of the Bay, hard clam populations are restricted to Tangier and Pocomoke sounds.

What does the hard clam eat?

Hard clams are filter-feeders on planktonic algae.

• While buried in the sand, the clam's two siphons stick up above the surface.
• Water is drawn down through the inhalant siphon.
• Food particles in the water are filtered out by the clam's gill cilia.
• Unused particles are periodically ejected through the exhalent siphon.

How does the hard clam reproduce?

Hard clams spawn better May and October, once the clams produce ripe gametes and the water temperature rises above 68 to 73 degrees.

• Females can release 16 to 24 million eggs per spawn. Eggs are fertilized in the water column.
• Free-swimming larvae develop for a week to 24 days. During this time they develop a foot, which is used to crawl and “explore” a surface before settlement.
• When they find a suitable surface to settle on, the larvae anchor themselves by thin threads secreted from a gland on the foot.
• The settled clam slowly metamorphoses into a juvenile clam, developing siphons, digestive viscera and gills.

Other facts about the hard clam:

• A long-lived species; individuals have been aged at more than 30 years.
• Native Americans used to use hard clam shells as wampum.
• Also called "quahogs," "littlenecks," "cherrystones" or "chowder clams." The various commercial names are based on the size of the clam.