''Isognomon radiatus'', the radial purse oyster or Lister's tree oyster, is a species of

bivalve Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class (biology), class of aquatic animal, aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed b ...

mollusc Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...

in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Isognomonidae Isognomonidae is a family of medium-sized to large saltwater clams. They are pearl oysters, marine bivalve molluscs in the superfamily Pterioidea Pterioidea is a superfamily of epifaunal marine bivalves mostly inhabiting continental shelf r ...

. It can be found along the Atlantic coast of North America, ranging from southern

Florida Florida ( ; ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders the Gulf of Mexico to the west, Alabama to the northwest, Georgia (U.S. state), Georgia to the north, the Atlantic ...

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

and

Bermuda Bermuda is a British Overseas Territories, British Overseas Territory in the Atlantic Ocean, North Atlantic Ocean. The closest land outside the territory is in the American state of North Carolina, about to the west-northwest. Bermuda is an ...

Description

Lister's tree oyster is an irregular, fan-shaped shell growing to about long. Each

valve A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or Slurry, slurries) by opening, closing, or partially obstructing various passageways. Valves are technically Pip ...

is a pale brown colour with whitish rays radiating from the umbo, the raised hump that is the first part of the shell to form when the animal is a juvenile. There are numerous sculptured concentric rings on the outside surface. It is attached to a hard

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (aquatic environment), the earthy material that exi ...

byssus A byssus () is a bundle of filaments secreted by many species of bivalve mollusc that function to attach the mollusc to a solid surface. Species from several families of clams have a byssus, including pen shells ( Pinnidae), true mussels (Mytili ...

threads and often occurs in clusters.

Distribution and habitat

Lister's tree oyster occurs in southern Florida, the Caribbean Sea and Gulf of Mexico, Bermuda, the West Indies, the Cayman Islands and Brazil. It grows, sometimes in dense patches, on the roots of mangroves and on shallow rocky areas, down to a depth of about . On coral reefs it occurs on rock ledges and exposed rocks in areas of high sedimentation, forming mats of hundreds of individual animals. It also grows on the shells of the Atlantic thorny oyster ('' Spondylus americanus''). In

Little Cayman Little Cayman is one of three Islands that make up the Cayman Islands. It is located in the Caribbean Sea, approximately 60 miles (96 km) northeast of East End, Grand Cayman and five miles (8 km) west of West End, Cayman Brac. Little ...

it occupies a particular zone on the lower shore and shallow subtidal region of sheltered bays where it is common under large stones, often accompanied by the rock boring urchin ('' Echinometra lucunter''). It also occurs in rock pools. In more exposed locations on the island it is replaced by the closely related flat tree oyster ('' Isognomon alatus''). Lister's tree oyster is a constituent of the characteristic invertebrate fauna of the mangrove swamps fringing the southern part of Florida.

References

{{Taxonbar, from=Q3017904 Pteriida Bivalves described in 1839