''Potamocorbula amurensis'' is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of small saltwater clam, a

marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military * ...

bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...

in the

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

Myida. Common names include the overbite clam, the Asian clam, the Amur River clam and the brackish-water corbula. The species is native to marine and

brackish Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuari ...

waters in the northern Pacific Ocean, its range extending from Siberia to China, Korea and Japan. It has become naturalised in San Francisco Bay.

Description

''Potamocorbula amurensis'' grows to a length of about . The umbo is about halfway along the hinge side of the shell and the shape of each valve is like a wide

isosceles triangle In geometry, an isosceles triangle () is a triangle that has two sides of equal length. Sometimes it is specified as having ''exactly'' two sides of equal length, and sometimes as having ''at least'' two sides of equal length, the latter versio ...

with rounded corners. The right valve is rather larger than the left so that it overlaps a little at the margin, a fact that distinguishes this species from other similar clams. The surface is smooth with faint concentric sculpture that is parallel to the margin. The general colour is cream, yellowish or light brown. In young individuals, a dark-coloured

periostracum The periostracum ( ) is a thin, organic coating (or "skin") that is the outermost layer of the shell of many shelled animals, including molluscs and brachiopods. Among molluscs, it is primarily seen in snails and clams, i.e. in gastropods and ...

covers the outer surface of each valve, but in older specimens this skin is largely worn away except for some wrinkled remnants at the valve margin. The part of the shell buried in the

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 (locomotion), the surface over which an organism lo ...

is clean, whereas the exposed portion is often colonised by other organisms which stain it a dark colour.

Distribution and habitat

The native range of ''Potamocorbula amurensis'', "of the

Amur River The Amur (russian: река́ Аму́р, ), or Heilong Jiang (, "Black Dragon River", ), is the world's List of longest rivers, tenth longest river, forming the border between the Russian Far East and Northeast China, Northeastern China (Inne ...

" is Siberia, China, Korea and Japan, between the latitudes of 53° N and 22° N. It has also become established in San Francisco Bay. It lives subtidally and on intertidal mud flats partially buried in soft sediment. It is tolerant of a wide range of salinities, ranging from about one part to thirty-three parts per thousand. In San Francisco Bay it is found subtidally in winter at and in summer occurs on exposed mud flats at . It is believed that it was transported across the Pacific in ballast water and discharged accidentally into the Bay around 1986.

Biology

''Potamocorbula amurensis'' lies semi-submerged in sediment, fixing itself in place by means of a few byssal threads. It has two short

siphons A siphon (from grc, σίφων, síphōn, "pipe, tube", also spelled nonetymologically 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 a ...

, through one of which (the upper, inhalant siphon) water is drawn into the shell. This water is passed over the

gill A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...

s, where oxygen and food particles such as bacteria,

phytoplankton Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'. Ph ...

and

zooplankton Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...

are removed. The water then passes out of the shell through the lower, exhalent siphon. This clam becomes sexually mature at the age of a few months. A single female can produce between 45,000 and 220,000 eggs. These are fertilised externally and spend about 18 days as planktonic veliger larvae which can disperse to other areas, before settling on the seabed.

Invasive species

There are concerns about ''Potamocorbula amurensis'' as an

invasive species An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species ad ...

San Francisco Bay San Francisco Bay is a large tidal estuary in the U.S. state of California, and gives its name to the San Francisco Bay Area. It is dominated by the big cities of San Francisco, San Jose, and Oakland. San Francisco Bay drains water from a ...

, where it became established in the 1980s. It has thrived there and in some places it is present at densities of more than 10,000 individuals per square metre (10.8 square feet). It out-competes native species and disrupts food chains by filtering

and

from the water and consequently depriving juvenile fish of their planktonic food. Another invasive species, the

European green crab European, or Europeans, or Europeneans, may refer to: In general * ''European'', an adjective referring to something of, from, or related to Europe ** Ethnic groups in Europe ** Demographics of Europe ** European cuisine, the cuisines of Europe a ...

, ''Carcinus maenas'', which arrived in the San Francisco Bay in around 1990, may control ''P. amurensis''. The green crab voraciously eats bivalves, including ''P. amurensis'', but may have other, unexpected, consequences.

References

{{Authority control Corbulidae Bivalves described in 1861 Taxa named by Leopold von Schrenck