An oyster drill resting on a rock.
An oyster drill resting on a rock.
E. Zabel, courtesy of URI

Oyster Drills
Atlantic Oyster Drill (Urosalpinx cinerea),
Thick-lipped Oyster Drill (Eupleura caudata)

Color: Dull brownish to grey shell with white points on both species.
Size: Thick-lipped oyster drill is up to 3/4 inch long; Atlantic oyster drill - up to 1 inch long.
Habitat: Seagrasses, oyster beds, and intertidal rocky bottoms.
Seasonal appearance: All year.

Description

Oyster drills are small predatory snails found in Rhode Island. The Atlantic oyster drill and the thick-lipped oyster drill are the two most common species. The shell of the Atlantic oyster drill is ribbed with a pointed spire, a flared outer lip with two to six teeth along the opening, and many rough and raised whorls and longitudinal ridges on the shell. The thick-lipped oyster drill is similar to the Atlantic oyster drill, but the anterior canal is longer with a smaller opening. This species resembles a small whelk or conch, with distinct channels of shell. The outer lip is thick with no flare and has six distinct teeth.

Life History and Behavior

The egg capsules of these snails can be found in spring and early summer. The eggs are small, urn-shaped, leathery cases generally found attached to pilings or mollusk shells.

Oyster drills are destructive little snails that prey directly on small shellfish, most notably the American oyster. Oyster drills attack their prey by making a small hole through the shell, using a drill-like organ called the radula. The radula is aided by the secretion of sulfuric acid to carve away the shell and make the hole. Once the hole is made, the animal will digest the soft meat of the prey. The mark left by an Oyster drill can be identified as wide, round holes tapering to a small point in the shells of mollusks. This is similar to the holes made by another predatory snail called the New England dog whelk, but is different from the many pockmark holes made by boring sponges.

Special Notes


Adapted from The Uncommon Guide to Common Life on Narragansett Bay. Save The Bay, 1998.