Eastern Oyster

Associated Smithsonian Expert: M. G. (Jerry) Harasewych, Ph.D.

Dr. Jerry Harasewych showing drawer of marine mollusk specimens

Photo by Smithsonian Institution

Dr. Jerry Harasewych is a Research Zoologist and Curator of Marine Mollusks at the Smithsonian National Museum of Natural History. His research specialties include the systematics and biogeography of several groups of deep-sea snails. He conducts field work using a variety of research submersibles to sample and observe these animals. Other areas of research include Antarctic mollusks and a highly diverse group of land snails endemic to the tropical western Atlantic. Harasewych first started to work with shells at the age of ten, when he began as a volunteer at the Academy of Natural Sciences in Philadelphia. He was an active member and officer of the Philadelphia Shell Club while pursuing an undergraduate degree in chemistry at Drexel University in Philadelphia. After completing his doctorate in Biological Oceanography at the College of Marine Studies of the University of Delaware, he moved to the D.C. area and became a Research Fellow in Clinical Neurogenetics at the National Institute of Mental Health. Harasewych joined the Smithsonian in 1985.

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California mussel
Courtesy of Josh Pederson, National Marine Sanctuaries Media Library, public domain


About Bivalves (Class Bivalvia): Defense

Bivalves have a hard shell made of minerals, typically layers of calcite and aragonite. The shell has two halves (valves) connected by a flexible ligament hinge. Powerful muscles contract to close the valves into a tight fit. Teeth along the edges of each valve interlock to keep them from sliding apart if the bivalve is attacked by a predator. The pattern of teeth, because it is often species-specific, is one feature used to identify bivalves. The shell grows over time, using calcium taken up from seawater or ingested food. Bivalves have no heads at all, and a flattened foot. The foot is shaped for wedging into sand, explaining why bivalves have also been called pelecypods (hatchet-feet). To keep from getting moved by water currents, bivalves tend to attach themselves to hard surfaces or burrow into sediments. They burrow by probing down with the foot (lengthening) and then retracting it (shortening) to tug the shell downward.

Queen scallop (Aequipecten opercularis) feeding
Courtesy of Kattegatcentret Gren†, via Biopix, CC-BY-NC


About Bivalves (Class Bivalvia): Feeding

Most bivalves filter food with their gills, then transport it to their mouths. While still used to get oxygen, their gills are modified to also act as food strainers. Typically, a special tube called a siphon serves as a straw to suck water through the bivalve's gills, and another siphon lets the water out after filtering has occurred. Tiny grooves in the gills are covered with hair-like cilia that trap particles passing by, such as microscopic plants (phytoplankton). Particles not accepted as food are sent to where they can be purged from the shell. Particles accepted as food are wiped off the gills by flaps (palps) and sent on to the bivalve's mouth. From there they travel to its complex stomach, where more cilia sort it out by size. Some bivalves are scavengers, scraping food from the sea bottom, or sucking in crustaceans or other prey with their siphons.

Related Resources
Scallops (Patinopecten caurinus) for sale at a market in Japan
Courtesy of Dr. Roger Mann, VIMS, via NOAA's Fisheries Collection, public domain

About Mollusks (Phylum Mollusca): Human Use

Mollusks have been exploited by people around the world for thousands of years. Both shelled (snails, clams, scallops, conchs) and unshelled mollusks (squid and octopus) have been popular food items since prehistoric times. Several early societies used shells such as cowries for money. Today, mollusk shells are often collected and sold. Even mollusk waste products have value. A pearl is just shell layers that the mollusk uses to cover debris that gets under its shell. All shelled mollusks make them, but it is the pearl oysters that sometimes make the symmetrical, shiny ones, essentially decorative pieces of dirt. Over the years, mollusks have been used for many other purposes: dyes, decorative inlays, medicines, blades, fishing lures, tweezers, and horns. Overharvesting has endangered many mollusks species, and cultivation of mollusks had emerged as one solution.