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Macoma Clams

The Baltic macoma clam has broad, oval-shaped shells, sometimes with a pinkish tint. (Aung/Wikimedia Commons)
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The Baltic macoma clam has broad, oval-shaped shells, sometimes with a pinkish tint. (Aung/Wikimedia Commons)

Macoma clams are tiny bivalves with thin, chalky white shells. They live buried in the sand or mud in the shallow waters of the middle and lower Chesapeake Bay.

Two species of macoma clams can be found in the Chesapeake Bay:

  • Baltic macoma clam, Macoma balthica
  • Narrowed macoma clam, Macoma tenta

Appearance:

  • Thin, fragile shells
  • The Baltic macoma clam has broad, oval-shaped shells, sometimes with a pinkish tint
  • The narrowed macoma clam’s shells are more elongated than the Baltic macoma’s. They also have a smooth, pearly sheen. The shells’ narrowed posterior end is slightly twisted to the left.
  • Two long, thin, flexible siphons that can be pulled completely inside the shells. One siphon is longer than the other.
  • Hatchet-shaped foot
  • The Baltic macoma clam is the larger of the two species, growing to 1.5 inches long. The narrowed macoma clam only grows to three-quarters of an inch long.

Habitat:

  • Burrows under the sand and mud along the shoreline and in shallow waters
  • Can lie either vertically or horizontally

Range:

  • Found throughout the middle and lower Chesapeake Bay

Feeding:

  • While buried in the sand, the clam’s two siphons stick up above the surface
  • The longer siphon sucks in tiny bits of food lying on the Bay’s bottom. It can also draw in water and filter out plankton.
  • Waste and unused water are ejected through the other siphon

Predators:

  • Macoma clams’ long siphons look like worms crawling along the bottom. They attract many predators, including American eels.

Reproduction and Life Cycle:

  • Release eggs and sperm into the water column
  • After being fertilized, eggs develop into larvae with two tiny, transparent shells and a small foot
  • Larvae float in the currents for a few weeks before eventually settling to the bottom
  • To avoid being tossed around by waves, larvae anchor themselves to sand grains using thin threads secreted from a gland on the foot

Other Facts:

  • Even though they are not as well-known as hard clams or soft shell clams, macoma clams are some of the most abundant clams in the Bay
  • Able to shift positions while buried in the sand. When disturbed, macoma clams will quickly burrow deeper.

Sources and Additional Information:




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