Surfclam Shells of the Mactridae Family

Three Surfclam Shells of the Mactridae Family can be found in this website:

Phylogeny: The Mactridae Family of Surfclams is in the phylum Mollusca. These shells are in the class Bivalvia, the subclass Autobranchia, the infraclass Heteroconchia, the subterclass Euheterodonta, the superorder Imparidentia, the order Venerida, and the superfamily Mactroidea. The Mactridae Family is one of four families in this superfamily. The Mactridae Family contains five subfamilies, thirty-eight genera, and around one hundred eighty-two species. The name Mactridae comes from the Greek word meaning ” kneading trough”. This refers to the deep trough-like condrophore in the hinge of these shells. These shells are also commonly known as Trough Shells or Mactrids.

Description: Mactrid Surfclams may be trigonal, ovate, or rhomboidal in outline. They are inflated in profile. The valves tend to be equilateral (same size and shape). These shells range in construction from translucently thin to very thick. There is usually a narrow gap between valves at the posterior end, and sometimes at the anterior end also. The posterior is usually offset by a keel or fringe. They may be smooth or sculpted commarginally with fine striations or coarse undulations. The interior margin is smooth. The interiors are non-nacreous. The hinge plate is strong and the internal ligament attaches in a deep chondrophore. Shells in this family a white, usually with a translucent to light brown periostracum. Mactrid Surf Clams are medium to large in size, with some reaching a maximum of 28 cm (11 inches) in length.

Habitat and Distribution:  Mactrid Surfclams are found buried in sand, mud, and other soft substrates. Most are active burrowers and may bury more than 33 cm (13 inches) deep. They live in the intertidal zone and to depths exceeding 200 m (656 feet). Some species have a high salinity tolerance, and some species can live in areas of entirely fresh water. Mactrid Surf Clams are found worldwide in polar to tropical seas. Nineteen species from the Mactridae Family are found in Mexican waters.

Natural History: Mactrid Surfclams are suspension feeders that filter plankton and fine detritus from the surrounding water. In turn their predators include birds, crabs, carnivorous mollusks, sea stars, and fish. They are gonochoric and reproduce sexually, through broadcast spawning, with external fertilization. The fertilized eggs hatch into planktonic larvae. Species in the Mactridae Family sometimes host symbiotic pea crabs or chemoautotrophic bacteria in the mantle cavity and gills. Mactrid Surfclams are edible and are sometimes the target of commercial fisheries, though less than many other clams.