''Modiolus modiolus'', common name northern horsemussel (

Scottish Gaelic Scottish Gaelic (, ; Endonym and exonym, endonym: ), also known as Scots Gaelic or simply Gaelic, is a Celtic language native to the Gaels of Scotland. As a member of the Goidelic language, Goidelic branch of Celtic, Scottish Gaelic, alongs ...

: , Scots: ), is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

of marine

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 ...

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

in the family

Mytilidae The Mytilidae are a family (biology), family of small to large Marine life, marine and Brackish water, brackish-water bivalve molluscs in the order (biology), order Mytilida. One of the genera, ''Limnoperna fortunei, Limnoperna'', even inhabits f ...

Description

''Modiolus modiolus'' is a large mussel growing to 22 cm (9ins) long though 10 cm (4ins) is a more typical size. The shell is purplish or dark blue and robust, with horny protuberances when young. The two valves are roughly triangular or bluntly oblong with rounded umbones near the anterior end. The annual growth lines are clear and there is a fine sculpturing of concentric grooves and ridges. The interior of the shell is white with a broad pallial line, large anterior adductor muscle scar and smaller posterior adductor muscle scar. The body is deep orange and the mantle is unfrilled. The shell is firmly attached to the substrate by

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.Horse mussel - ''Modiolus modiolus''
Marine Life Information Network. Retrieved 2011-11-01. In

, the species is called 'clabaidh-dubha' ('clabby doos'), meaning 'big black mouths'. More recently in

Scotland Scotland is a Countries of the United Kingdom, country that is part of the United Kingdom. It contains nearly one-third of the United Kingdom's land area, consisting of the northern part of the island of Great Britain and more than 790 adjac ...

the species is commonly known and referred to as 'clappy-doo'. In the

Shetland Shetland (until 1975 spelled Zetland), also called the Shetland Islands, is an archipelago in Scotland lying between Orkney, the Faroe Islands, and Norway, marking the northernmost region of the United Kingdom. The islands lie about to the ...

dialect, they are known as "".

Right and left valve of the same specimen: File:Modiolus modiolus 0001.jpg, Right valve File:Modiolus modiolus 0002.jpg, Left valve

Distribution

''M. modiolus'' can be found along the Atlantic coast of North America, from the

Arctic Ocean The Arctic Ocean is the smallest and shallowest of the world's five oceanic divisions. It spans an area of approximately and is the coldest of the world's oceans. The International Hydrographic Organization (IHO) recognizes it as an ocean, ...

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 ...

, and along the Pacific coast, from the Arctic Ocean to

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

. It is also found on the European seaboard of the Atlantic Ocean from the United Kingdom northwards. It is found from low tide mark to depths of 50 metres in British waters and 80 metres off the coast of

Nova Scotia Nova Scotia is a Provinces and territories of Canada, province of Canada, located on its east coast. It is one of the three Maritime Canada, Maritime provinces and Population of Canada by province and territory, most populous province in Atlan ...

. The largest horse mussel bed in Scotland is near Noss Head in Caithness. While it is also found in the

Baltic Sea The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by the countries of Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden, and the North European Plain, North and Central European Plain regions. It is the ...

, it has become a

vulnerable species A vulnerable species is a species which has been Conservation status, categorized by the International Union for Conservation of Nature as being threatened species, threatened with extinction unless the circumstances that are threatened species, ...

there.

Ecology

''M. modiolus'' is found growing on hard substrates including shells and stones and the byssus threads of other mussels. Survival rates of young individuals are low but by the time they reach about 4 cm long, at an age of 4 years, individuals are too large and tough to be predated upon by

starfish Starfish or sea stars are Star polygon, star-shaped echinoderms belonging to the class (biology), class Asteroidea (). Common usage frequently finds these names being also applied to brittle star, ophiuroids, which are correctly referred to ...

such as '' Asterias rubens'', the whelk ''

Buccinum undatum ''Buccinum undatum'', the common whelk or the waved buccinum, is a large, edible Marine (ocean), marine gastropod in the family (biology), family Buccinidae, the "true whelks".Fraussen, K.; Gofas, S. (2014). Buccinum undatum Linnaeus, 1758. Acces ...

'' and crabs. Juveniles growing on byssus threads are more likely to survive than free living individuals and this results in the formation of cold-water reefs of mussels.''Modiolus modiolus''
UK Marine SAC's Project. Retrieved 2011-11-01. These mostly occur in locations with fairly strong currents. The species is tolerant of low levels of oxygen and of a diminished quantity of the

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

on which they feed. The boring sponge '' Cliona celata'' sometimes damages the shells of older individuals.Comely, C.A., (1978). Modiolus modiolus (L.) from the Scottish West coast. I. Biology. Ophelia, 17, 167-193.

References

{{Authority control modiolus Bivalves described in 1758 Taxa named by Carl Linnaeus Bivalves of North America