Three species of arks can be found in the Chesapeake Bay: the ponderous ark, Noetia ponderosa, the blood ark, Anadara ovalis, and transverse ark, Anadara transversa.

Arks have thick, white, boxy shells with many ribs. Ponderous arks are heart-shaped when viewed from the side. Blood arks and ponderous arks are often covered with a thick, dark brown, felt-like "periostracum," or outer-most layer. The ponderous ark is the largest of the three species, growing to 2.5 inches in length. The transverse ark is the smallest, growing to about 1 inch in length.


Arks eat plankton and detritus, feeding through a figure eight-shaped opening in the mantle.

Reproduction and Life Cycle

Spawning occurs throughout most of the year, with peaks in summer and autumn. As a juvenile and adult, an ark will settle on the bottom and use its foot to anchor itself.

Did You Know?

  • Arks’ thick, heavy shells are able to withstand strong waves and currents.
  • Ark shells are often found washed up on lower Bay beaches.
  • The blood ark gets its name from its red blood; most other bivalves have clear blood.

Sources and Additional Information