Common name: flag pen shell

General information

The Pen Shell, scientifically known as Atrina vexillum, is a species of large saltwater clam in the family Pinnidae. These bivalves are known for their elongated, pen-like shells, which can be quite striking in appearance. They are filter feeders and play a role in maintaining water quality by sifting out plankton and organic particles from the water column.

Care

Pen Shells require a sandy or muddy substrate in which they can anchor themselves using their byssal threads. They are sensitive to water quality and require stable conditions with low levels of nitrates and phosphates. Adequate water flow is necessary to bring food particles to them, but strong currents should be avoided as they can dislodge the shells.

Reproduction

Atrina vexillum is a broadcast spawner, releasing eggs and sperm into the water column where fertilization occurs. In the aquarium, spawning can be triggered by changes in water temperature or conditions, but raising the larvae to maturity is challenging and rarely attempted by hobbyists.

Symbiosis

While not known for any specific symbiotic relationships in the aquarium trade, in the wild, Pen Shells can host a variety of epibionts, including algae, sponges, and other invertebrates, which can add to the biodiversity of a reef tank.

Habitat

Pen Shells are typically found in sandy or muddy bottoms in shallow waters. They are distributed in various parts of the world, including the Indo-Pacific region. In the aquarium, they should be provided with a deep sand bed to mimic their natural habitat.