Biology Photo of the Month - January - February 2003

Scallop eyes

Common Bay Scallop, Aequipecten irradians (from northern Gulf of Mexico)

Text by Augsburg biology student Natalie Lanzatella
Photos by Bill Capman

Update - November 2003
Scallop photo on cover of British Journal of Ophthalmology

Close-up view of the brilliantly iridescent blue eyes of a scallop in Augsburg's marine aquaria
(move mouse over image for a wider view)

Many people know of scallops as a tasty seafood, but most have never seen a living scallop. Scallops are diverse, with over 300 species of scallops living on the ocean floor worldwide. They range from shallow waters to areas several hundred feet deep. Scallops, classified as bivalve mollusks, hide some amazing secrets. For one, about sixty primitive tiny bright blue eyes eyes reside in rows along a scallop’s mantle edge to detect motion, light and dark. A scallop can easily regrow any lost or injured eyes. Although these eyes may or may not produce clear images, the ability to sense an object moving with the speed of one of the scallop’s predators allows the scallop to save its skin (or to be scientifically correct, its shells) by either shutting immediately or swimming away.

Secondly, scallops possess an unusual trait which most other bivalves lack: the ability to swim. Scallops can propel themselves away from danger by contracting their powerful muscles and "clapping" their shells together, forcing water out through openings on both sides of their shell hinge. They can move forwards backwards, make turns, and right themselves in this fashion. Scallops swim particularly when faced with a predator (e.g., a seastar). Otherwise, if left relatively undisturbed, scallops are fairly sedentary creatures that lie on the seafloor as they feed by filtering microorganisms from the water.

Those tasty cylindrical or disk-shaped morsels of scallop meat found in seafood shops are the adductor muscles that in the living scallops make their unique swimming ability possible.

The distinctive shape of scallop shells (with fin-like extensions on each
side of the hinge), is familiar as the logo for a well-known oil company.


Click photo for larger view (and see close-up at right)

Scallops normally rest on the on the seafloor with shells partially open to allow water to be pumped past the gills for filter-feeding and gas exchange.

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Numerous fleshy tentacles extend from the mantle, looking like menacing teeth in this photo. These tentacles have sensory roles, helping to alert the scallop to danger that might warrant clapping the shells shut for protection, and they serve as a sort of sieve to prevent large particles from entering the mantle cavity (within which the delicate gills are exposed).

Click photo for MUCH larger view (256 KB)
The fleshy mantle that lines a scallop's shells encloses an interior space (the mantle cavity), which houses the gills (visible above) and the visceral mass. Microscopic beating hairs (cilia) on the gills create water currents. Water flows through the mantle cavity past the gills, bringing oxygen to the gills as well as microscopic food particles. Food particles captured on the gill surfaces are transported by cilia to the mouth (the mouth is not visible when viewing a live scallop).

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Archive of past photos and stories