Shell of the Week: The Elusive Atlantic Geoduck

Panopea bitruncata from Mexico Beach, Florida Panhandle. Illustration by José H. Leal for the Eastern Seaboard Project.

Panopea bitruncata is a large bivalve closely related to the famous Pacific Geoduck (Panopea generosa). The Atlantic species is very uncommon.Geoducks (goo·ee·duhks) are members of the bivalve family Hiatellidae. They live buried in mud, have long siphons that cannot fully retract into the shell, and a shell with valves that do not completely shut when joined together.

Panopea bitruncata from Cayo Costa, collected by Captain Brian Holloway in February 2024. Illustration by José H. Leal.

The maximum reported length for the Atlantic Geoduck is 190 mm (7.48 inches), and the single valve in the second image (above), found by Captain Brian Holloway on Cayo Costa in February 2024, measures 185 mm (7.28 inches)! In 1936, R. A. McLean* reported a valve of the species found on Sanibel Island by Dr. Louise M. Perry. Its geographic range encompasses the southeastern coast of the US from North Carolina to Florida and around the northern Gulf of Mexico to Texas.

*McLean, R. A. 1936. Panope [sic] bitruncata Conrad at Sanibel, Florida. The Nautilus 49(3): 104.