Abra alba
Encyclopedia
Abra alba or the white furrow shell is a species
of bivalve mollusc in the Semelidae
family
. It occurs in the north eastern Atlantic Ocean and the Mediterranean Sea, where it lives on the floor in shallow areas buried in soft sediments.
. The shape is roughly oval and the posterior and anterior dorsal margins are almost straight and slope to rounded ends. Both margins are smooth and the anterior margin is a little longer than the posterior one. The valves have a sculpture of fine concentric lines and the growth stages of the animal are visible. The interior of the valves is somewhat glossy and the adductor muscle scars may be visible. The small brown ligament that holds the valves together is exterior.
at depths down to 200 m (656 ft). It is common around the British Isles and in the North Sea
. It prefers fine, silty sand, but is also found in mud or gravel.
. It is mostly a deposit feeder but is also able to feed on suspended particles as does the tellin
Tellina fabula
, a species with which it is often associated. The inhalant siphon gropes around widely over the surface of the substrate, actively drawing in detritus. In studies of Liverpool Bay
, a community
that includes A. alba, Phaxas pellucidus
(the transparent razor shell) and Lagis koreni
(the trumpet worm) is likely associated with more than one habitat
.
A large number of very small eggs are produced from May to August. The larvae probably have a lengthy period as part of the zooplankton
before settling out. Juveniles grow fast during the summer but the ones that settle in autumn seem to delay their further development until the following spring. The lifespan is usually one year but can extend to two.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of bivalve mollusc in the Semelidae
Semelidae
The Semelidae are a family of clams, marine bivalve molluscs of the order Veneroida.-Characteristics:Menbers of this family have rounded or oval, elongated shells, much flattened. The two valves are connected by an internal ligament in contrast to the closely related family Tellinidae where the...
family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
. It occurs in the north eastern Atlantic Ocean and the Mediterranean Sea, where it lives on the floor in shallow areas buried in soft sediments.
Description
Abra alba can grow to up to 2.5 cm (0.984251968503937 in) long but a more usual size is 1.5 centimetres. It has a pair of thin brittle valves that are translucent, semi-shiny and a dirty white colour with a pale brown periostracumPeriostracum
The periostracum is a thin organic coating or "skin" which is the outermost layer of the shell of many shelled animals, including mollusks and brachiopods. Among mollusks it is primarily seen in snails and clams, i.e. in bivalves and gastropods, but it is also found in cephalopods such as the...
. The shape is roughly oval and the posterior and anterior dorsal margins are almost straight and slope to rounded ends. Both margins are smooth and the anterior margin is a little longer than the posterior one. The valves have a sculpture of fine concentric lines and the growth stages of the animal are visible. The interior of the valves is somewhat glossy and the adductor muscle scars may be visible. The small brown ligament that holds the valves together is exterior.
Distribution
Abra alba is found on the coasts of north-west Europe and the Mediterranean SeaMediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
at depths down to 200 m (656 ft). It is common around the British Isles and in the North Sea
North Sea
In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean. In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively...
. It prefers fine, silty sand, but is also found in mud or gravel.
Biology
Abra alba feeds by means of a pair of separate long, extensible siphons, elongations of the mantleMantle (mollusc)
The mantle is a significant part of the anatomy of molluscs: it is the dorsal body wall which covers the visceral mass and usually protrudes in the form of flaps well beyond the visceral mass itself.In many, but by no means all, species of molluscs, the epidermis of the mantle secretes...
. It is mostly a deposit feeder but is also able to feed on suspended particles as does the tellin
Tellina
Tellina is a widely distributed genus of marine bivalve molluscs, in the family Tellinidae.- Species :* Tellina aequistriata Say, 1824: striate tellin* Tellina agilis Stimpson, 1857: northern dwarf tellin, northern dwarf-tellin...
Tellina fabula
Tellina fabula
Tellina fabula is a species of marine bivalve mollusc in the family Tellinidae. It is found off the coasts of north west Europe where it lives buried in sandy sediments....
, a species with which it is often associated. The inhalant siphon gropes around widely over the surface of the substrate, actively drawing in detritus. In studies of Liverpool Bay
Liverpool Bay
Liverpool Bay is a bay of the Irish Sea between northeast Wales, Cheshire, Lancashire and Merseyside to the east of the Irish Sea. The bay is a classic example of a region of freshwater influence...
, a community
Community (ecology)
In ecology, a community is an assemblage of two or more populations of different species occupying the same geographical area. The term community has a variety of uses...
that includes A. alba, Phaxas pellucidus
Phaxas pellucidus
Phaxas pellucidus or the transparent razor shell is a species of marine bivalve mollusc in the family Pharidae. It is found buried in the seabed in coastal waters of northwest Europe, often in great numbers.-Description:...
(the transparent razor shell) and Lagis koreni
Lagis koreni
Lagis koreni, commonly known as the trumpet worm, is a species of marine polychaete worm found in European waters. It lives within a narrow conical tube tube made of grains of sand and shell fragments.-Taxonomy:...
(the trumpet worm) is likely associated with more than one habitat
Biotope
Biotope is an area of uniform environmental conditions providing a living place for a specific assemblage of plants and animals. Biotope is almost synonymous with the term habitat, but while the subject of a habitat is a species or a population, the subject of a biotope is a biological community.It...
.
A large number of very small eggs are produced from May to August. The larvae probably have a lengthy period as part of the zooplankton
Zooplankton
Zooplankton are heterotrophic plankton. Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word "zooplankton" is derived from the Greek zoon , meaning "animal", and , meaning "wanderer" or "drifter"...
before settling out. Juveniles grow fast during the summer but the ones that settle in autumn seem to delay their further development until the following spring. The lifespan is usually one year but can extend to two.