Arks - Chesapeake Bay Program

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A white and slightly pink blood ark shell rests on top of the sand.
Ark shells, like this blood ark, are often found bleached white and washed up on lower Bay beaches. (Photo courtesy of Wayne Longbottom/iNaturalist CC BY-NC, cropped and toned)

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Small image of A white and slightly pink blood ark shell rests on top of the sand. Small image of A small blood ark shell covered with thick, dark brown spikes. Small image of A blood ark is anchored into the sand, its shell partly open. Small image of A close-up view of a transverse ark, which is mostly white with light pink at the edges. Small image of A close-up view of a transverse ark shows its ribbed shells.

Quick Facts

Species type

Native

Size

Ponderous ark grow up to 2.5 inches in length; transverse ark grow 1 inch in length

Habitat

Burrow into bottom sediments, using their large foot to firmly achor themselves; blood arks live in shallow waters, ponderous arks live in both shallow and deep waters and transverse arks often do not burrow, but rather live among bay grass stems

Range

Found in the salty waters of the lower Chesapeake Bay.

Diet

Feeds on plankton and detritus

Lifespan

Up to 30 years

Conservation status

Stable

Appearance

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.

Feeding

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

  • Life in the Chesapeake Bay by Alice Jane Lippson and Robert L. Lippson
  • Ponderous Ark – Bailey-Matthews National Shell Musuem
  • Ark Clams – Barnegat Bay Shellfish
Tags:
  • Invertebrates
  • Mollusks
  • Open & Shallow Waters

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Northern Sea Robin Prionotus carolinus

Chinese mitten crab Eriocheir sinensis

Arks Family: Arcidae

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