Ark Shells of the Arcidae Family

Nine Ark Shells of the Arcidae Family can be found in this website:

Phylogeny: The Ark Shells of the Arcidae Family (Lamark, 1809), are bivalve mollusks in the Arcida order. Shells in this order are characterized by having a straight hinge, with taxodont dentition. They also are isomyariam, meaning their two adductor muscles are equal in size. Shells in this order are found exclusively in marine environments. There are two superfamilies in the Arcoda order – Arcoidea and Limopsoidea.  Limopsoideans tend to be oval in shape while Arcoidea are more quadrate. The Arcidae Family falls in the superfamily Arcoidea. The Arcidae Family consists of one hundred eighty-nine species that have been placed in thirty genera. Arcidae Family Ark Shells differ from Ark Shells in the Noetidae Family Ark Shells in the placement of ligaments and the lack of striations on the ligaments. Ark Shells look like an ark or treasure chest, from which they derive their common name. These shells are also commonly known as Arcids.

Description: Ark Shells are strongly built, small to large-sized, shells. There is considerable variation between species. Generally, they are trapezoidal, trigonal, or quadrate in profile. They are equivalve and strongly inflated. Their hinge line is arched and there are numerous teeth along the hinge line of both valves that align, like a zipper, when the shell is closed. Most are sculpted with strong radial ribs. Some also have commarginal ribs. Most shells in this Family are white or white with brown. Many Ark Shells are covered with a heavy periostracum (outer membrane), usually dark brown in color. Ark Shells can reach up to 16.0 cm ( 6.25 inches) in length, though most are around half that size.

Habitat and Distribution: Ark Shells may be found in sand or mud substrates or attached to stones or rocks by byssus (thread-like anchor lines). Some even burrow into rock. They are found from shallow to very deep waters, with some exceeding 5,100 m (16,728 feet) in depth. Ark Shells have a global distribution, with most found in warmer waters. There are at least thirty-five species of Ark Shells found in Mexican waters.

Natural History: Ark Shells are suspension feeders that filter plankton and fine detritus from the surrounding water. Their predators include birds, crabs, carnivorous mollusks and rays. They are gonochoric and reproduce sexually, through broadcast spawning, with external fertilization. They  reach reproductive maturity when they are twelve months old and they have life-spans of six  years. Ark Shells differ from most bivalves in that they have red blood pigments (hemoglobin) that facilitate the transport of oxygen to their tissues, which allows them to inhabit more hypoxic environments. Ark Shells have been harvested as a food source and for fishing bait since pre-historic times.  Today, are raised in aquaculture farms in some regions.