White-sand Macoma

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

VIDEO LIBRARY

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

VIDEO LIBRARY

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.

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Snail (Indrella ampulla) defecating
Courtesy of Vipin Baliga, via Flickr: EOL Images, CC-BY-NC-SA

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About Mollusks (Phylum Mollusca): Feeding

Most mollusks have a "radula", a ribbon made of chitin with rows of teeth (denticles). The radula is always used to feed, but how it is used varies widely. Radulas are specialized to the diets of mollusks, which range from fully carnivorous to entirely herbivorous. The radula may be used to filter, scrape, crush, cut, or stab, depending what food is eaten. Predatory murexes use the radula to drill holes into other mollusks, whereas limpets use it to scrape algae off rocks. The shape of the radula and denticles can be used to figure out what mollusk it came from. Nudibranchs that feed on corals have long, skinny denticles for scraping the thin layer of flesh off the coral skeleton. Queen conchs have a comb-like radula with thousands of tiny denticles for filtering small food from the water. Regardless, as denticles wear away, they are continuously replaced from top to bottom.