Arcida
Arcida is an order of marine bivalve mollusks that includes about 100 species. They are commonly known as ark shells, ark clams, blood clams, and cockles. Arcidae are an ancient group, with fossils dating back to the Ordovician period.
Characteristics
Arcid bivalves are characterized by their elongated, ark-shaped shells with a distinct dorsal hinge line. Their shells are typically thick and heavy, and they often have strong ribs or ridges. The anterior end of the shell is rounded, while the posterior end is truncated. Most Arcids have small, pointed teeth along the hinge line, and ligaments connect the two valves. Their shells are often brightly colored, with hues of white, yellow, brown, orange, and red.
Arcids are infaunal, meaning they burrow into the sediment. They are filter feeders, using their gills to extract food from the water. They reproduce sexually, and their larvae are planktonic before settling to the seafloor.
Environment
Arcids are found in a variety of marine environments, including intertidal zones, subtidal areas, and deep-sea habitats. They are most abundant in warm, shallow waters with sandy or muddy bottoms. Arcids can tolerate a wide range of salinity levels and are found in both coastal and offshore environments.
Examples of Species
Some common examples of Arcidae species include:
- Arca zebra (Zebra Ark Shell)
- Anadara transversa (Blood Clam)
- Noetia ponderosa (Ponderous Ark Shell)
- Barbatia gracillima (Gracile Ark Shell)
- Scapharca inaequivalvis (Common Ark Shell)