''Mytilicola orentalis'' (known as 'oyster redworm' or 'red worm disease') is an intestinal copepod parasite of bivalves with a direct life cycle. It is native to the waters around

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

and was first described in the

Japanese Sea The Sea of Japan is the marginal sea between the Japanese archipelago, Sakhalin, the Korean Peninsula, and the mainland of the Russian Far East. The Japanese archipelago separates the sea from the Pacific Ocean. Like the Mediterranean Sea, it h ...

and was introduced to

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

in the 1960s and 70's with

oyster Oyster is the common name for a number of different families of salt-water bivalve molluscs that live in marine or brackish habitats. In some species, the valves are highly calcified, and many are somewhat irregular in shape. Many, but not al ...

imports. Since then it has also been observed in the Wadden and the

Baltic Sea The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden and the North and Central European Plain. The sea stretches from 53°N to 66°N latitude and from ...

. It has a wide range of host species in both its native range and in Europe.

Ecology

In a naturally infected population of pacific oysters 14% of the oysters were infected, with up to 20 ''M. orientalis'' in one oyster. The diet of this parasitic species in the blue mussel host consists of both host tissue and organic material in the gut of the host. The latter means that in some respects the species can be seen as a

commensal Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit fro ...

and does not have to negatively impact its host. Females are often larger than males.

Distribution and host species

''Mytilicola orentalis'' originates in the Japanese Sea and is known to occur on the Pacific coast of the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

and Europe. Since its introduction in Europe it has been observed across European waters, including locations in France, Ireland, the United Kingdom and the Netherlands. Although this is a marine species, it has been observed in mussels in

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 ...

water in the

Kiel bay The Bay of Kiel or Kiel Bay (, ; ) is a bay in the southwestern Baltic Sea, off the shores of Schleswig-Holstein in Germany and the islands of Denmark. It is connected with the Bay of Mecklenburg in the east, the Little Belt in the northwest, ...

. Host species in the native range include a wide variety of

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 ...

species. These include, but are not limited to, '' Barnea dilatata japonica'', ''

Barnea manilensis Barnea may refer to: * Barnea is an olive cultivar, see List of olive cultivars There are hundreds of cultivars of the olive (''Olea europaea''). As one of the oldest and more important domesticated crops raised by humans, the olive tree has dive ...

'', the blue mussels, the

Mediterranean mussel The Mediterranean mussel (''Mytilus galloprovincialis'') is a species of bivalve, a marine (ocean), marine mollusc in the family (biology), family Mytilidae. It is an invasive species in many parts of the world, and also an object of aquaculture ...

, the

pacific oyster The Pacific oyster, Japanese oyster, or Miyagi oyster (''Magallana gigas''), is an oyster native to the Pacific coast of Asia. It has become an introduced species in North America, Australia, Europe, and New Zealand. Etymology The genus ''Mag ...

, the

European flat oyster 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 ...

, and the Japanese carpet shell. ''Mytilicola orentalis'' infection in pacific oysters correlates with the

co-infection Coinfection is the simultaneous infection of a host by multiple pathogen species. In virology, coinfection includes simultaneous infection of a single cell by two or more virus particles. An example is the coinfection of liver cells with hepatiti ...

with ''Polydora'' sp. In the Mytilida co-infections between ''M. orientalis'' and '' M. intestinalis'' sometimes occur.

References

{{Taxonbar, from=Q4309134 Cyclopoida