Spoonclam Shells of the Periplomatidae Family
One Spoonclam of the Periplomatidae Family can be found in this website:
Western Spoonclam Shell, Periploma planiusculum. A representative of the Periplomatidae Family of Spoon Clams.
Phylogeny: Spoonclams of the Periplomatidae Family of Spoonclam Shells are in the phylum Mollusca and the class Bivalvia. They are in the subclass Autobranchia, the infraclass Heteroconchia, the subterclass Euheterodonta, the superorder Anomalodesmata, and the superfamily Thracioidea. The family Periplomatidae is one of four families in this superfamily. The Periplomatidae Family contains six genera and forty-two species. The name Periplomatidae comes from the Greek words meaning “around dirty water” or “around muddy place”, this refers to the habitat these shells usually live in. Spoonclams get their common name from their spoon-shaped condrophore. Species in this family are also known as Ghost Clams or False Clams.
Description: Spoonclams can vary widely in their shape and structure. They may be ovate, elongate, quadrate, trigonal, or circular in outline. Most have thin, fragile shells, but some are of heavier construction. They are inflated in profile, but they are inequivalve in that the right valve is generally more convex than the left, but sometimes the left is more convex. The right valve often overlaps the left. These shells may be weakly sculpted with commarginal undulations, and, rarely, radial ridges. The umbones (apex of the shell) are prominent and have an intrinsic fracture that proceeds ventrally for some distance and is reenforced with extra shell material on the interior surface. Spoonclams have simple hinges that lack conventional teeth, with their function being taken over by a spoon-shaped chondrophore (attachment point for hinge ligament) in either valve. These shells are whitish in color. The exterior may be prismatic, and the interior is nacreous. Spoonclams have a thin periostracum, which, in some cases, are coated with cemented sand grains. They a medium sized bivalves, reaching at least 7.5 cm (2.9 inches) in length, with some sources extending that length to 10 cm (3.9 inches).
Habitat and Distribution: Spoonclams are found buried in silty sand or muddy substrates. They favor the protected waters of estuaries, bays, and deeper waters. They are often associated with mangroves and sea grass beds. Most species live between the lower intertidal zone and depths up to 50 m (164 feet) but one species reaches 1,030 m (3,378 feet). Spoonclams are found worldwide in boreal to tropical seas. At least ten species from this family are found in Mexican waters.
Natural History: Spoonclams are suspension and depositional feeders that filter plankton and fine detritus from the surrounding water and surface of the substrate. Their predators include shorebirds, crabs, carnivorous mollusks, and rays. They are simultaneous hermaphrodites (having both male and female reproductive organs) and reproduce sexually, through broadcast spawning, with external fertilization. The eggs develop into free-swimming trochophore larvae, which transition into bivalve veliger larvae resembling miniature clams. Some species in this family are capable of self-fertilization. While these clams are edible, they are not the subject of widespread commercial or recreational harvesting. Given the habitats in which they are found, and since they accumulate chemicals and metals from their environment, it may not be safe to consume them in large quantities.