Myida (formerly Myoida) is an

order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...

of saltwater and freshwater clams, marine and

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include non-salty mi ...

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 ...

s in the subclass

Heterodonta Heteroconchia is a Taxonomy (biology), taxonomic infraclass of diverse bivalve molluscs, belonging to the subclass Autobranchia. This infraclass includes the cockle (bivalve), cockles, Venus clams, the Unionida, freshwater mussels, Palaeoheterod ...

. The order includes such bivalves as

soft-shell clam Soft-shell clams (American English) or Sand gaper (British English/Europe), scientific name ''Mya arenaria'', popularly called "steamers", "softshells", "piss clams", "Ipswich clams", or "Essex clams", are a species of edible saltwater clam, a ...

geoduck The Pacific geoduck ( ; ''Panopea generosa'') is a species of very large saltwater clam in the family Hiatellidae. The common name is derived from the Lushootseed name, . The geoduck is native to the coastal waters of the eastern North Pacific ...

s and

shipworm The shipworms, also called teredo worms or simply teredo (, via Latin ), are marine bivalve molluscs in the family Teredinidae, a group of saltwater clams with long, soft, naked bodies. They are notorious for boring into (and commonly eventual ...

Description

They are burrowing molluscs with well-developed

siphon A siphon (; also spelled syphon) is any of a wide variety of devices that involve the flow of liquids through tubes. In a narrower sense, the word refers particularly to a tube in an inverted "U" shape, which causes a liquid to flow upward, abo ...

s. The shell is relatively soft and lacks a

nacre Nacre ( , ), also known as mother-of-pearl, is an organicinorganic composite material produced by some molluscs as an inner shell layer. It is also the material of which pearls are composed. It is strong, resilient, and iridescent. Nacre is ...

ous layer. Some species have a single cardinal tooth.

Superfamilies and families

Superfamilies and families within the Myida include (the use of † indicate taxa that are extinct): * Superfamily: Dreissenoidea ** Family:

Dreissenidae The Dreissenidae are a family of small freshwater aquatic bivalve molluscs, commonly called ''mussels'' although not at all closely related to true mussels. The shells of these bivalves are shaped somewhat like those of true mussels, which they ...

* Superfamily: Myoidea ** Family:

Corbulidae Corbulidae is a family of very small saltwater clams, marine bivalve molluscs in the order Myida. Genera and species Genera and species in the family Corbulidae include: * '' Anisocorbula'' Iredale, 1930 * '' Apachecorbula'' Olivera, 2014 ** '' ...

** Family:

Myidae Myidae, common name the softshell clams, is a Taxonomy (biology), taxonomic family (biology), family of marine (ocean), marine bivalve molluscs in the order (biology), order Myida. Genera Genera within the family Myidae include: * ''Cryptomya'' ...

** Family: † Pleurodesmatidae ** Family: † Raetomyidae * Superfamily: Pholadoidea ** Family:

Pholadidae Pholadidae, known as piddocks or angelwings, are a family (biology), family of bivalve molluscs similar to a clam. Background Piddocks are unique in that each side of their shells is divided into 2 or 3 separate sections. Furthermore, one of the ...

** Family:

Teredinidae The shipworms, also called teredo worms or simply teredo (, via Latin ), are marine bivalve molluscs in the family Teredinidae, a group of saltwater clams with long, soft, naked bodies. They are notorious for boring into (and commonly eventual ...

** Family:

Xylophagaidae Xylophagaidae is a family of deep-sea woodboring bivalve molluscs, similar to shipworms The shipworms, also called teredo worms or simply teredo (, via Latin ), are marine life, marine bivalve molluscs in the family Teredinidae, a group of ...

* Superfamily: † Pleuromyoidea ** Family: † Ceratomyidae ** Family: † Pleuromyidae ** Family: † Vacunellidae

References

* Powell A W B, ''New Zealand Mollusca'', William Collins Publishers Ltd, Auckland, New Zealand 1979

External links

Animaldiversity

Taxonomicon
Bivalve orders {{bivalve-stub