''Arca noae'' or the Noah's Ark shell 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), ...

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 ...

in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Arcidae. It is found in the

Mediterranean Sea The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern Eur ...

from low tide mark to a depth of .

Description

The shell of ''Arca noae'' grows to about 10 cm (4 in) in length. It is shortened at the anterior end and elongated posteriorly. It is irregularly striped in brown and white and has finely sculptured ribs running from the umbones to the margin. The hinge is long and straight and the shell is attached strongly to 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 (aquatic environment), the earthy material that exi ...

by byssal threads. There are pallial eyes on the edges of the mantle, especially at the posterior end.

Right and left valve of the same specimen: File:Arca noae 0001.jpg, Right valve File:Arca noae 0002.jpg, Left valve var. ''abbreviata'' File:Arca noae 0003.jpg, Right valve File:Arca noae 0004.jpg, Left valve

Distribution

''Arca noae'' is found in the Mediterranean Sea. It was once common in the Adriatic, but in 1949/50 there was a sudden unexplained, catastrophic decline in numbers. Since then, populations have been creeping back upwards, and in 2002, densities of up to 13 individuals per square metre (11 square feet) were recorded. However, due to a lack of records, it is unclear whether the population had returned to its previous size.

Biology

In the lower part of the intertidal zone in the Adriatic, ''Arca noae'' often grows in association with ''

Modiolus barbatus ''Modiolus barbatus'', the bearded horse mussel, is a species of "horse mussel", a marine (ocean), marine bivalve mollusc in the family (biology), family Mytilidae, the mussels. The fossil record of this species dates back to the Pliocene (age r ...

''. The shells are often heavily encrusted with

epibiont An epibiont (from the Ancient Greek meaning "living on top of") is an organism that lives on the surface of another living organism, called the basibiont ("living underneath"). The interaction between the two organisms is called epibiosis. An ep ...

s. Water is drawn into the shell mainly at the posterior end. Plankton and fine organic particles are filtered out as the water passes over the gills and inedible particles are rejected at the same time.

Uses

''Arca noae'' is fished commercially in the Adriatic Sea, either by divers gathering individual shells by hand or from boats using specially adapted rakes which are pulled along the seabed. The shellfish are then sold in local markets.

References

{{Taxonbar, from=Q632517 Arcidae Bivalves described in 1758 Taxa named by Carl Linnaeus