''Fabulina fabula'', the bean-like tellin, is a species of marine bivalve mollusc in the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Tellinidae The Tellinidae are a family of marine bivalve molluscs of the order Cardiida. Commonly known as tellins or tellens, they live fairly deep in soft sediments in shallow seas and respire using long siphons that reach up to the surface of the sedime ...

. It is found off the coasts of northwest Europe, where it lives buried in sandy sediments. Bivalves are molluscs with a body compressed between two usually similar shell valves joined by an elastic ligament. There are teeth at the edge of the shell and the animal has a muscular foot,

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, siphons, mouth and gut and is surrounded by a mantle inside the shell.

Description

The shell of ''Fabulina fabula'' is brittle and flattened and grows to a length of twenty millimeters. The outline is oval but the shell is asymmetric with the hinge slightly off centre and the beaks slightly behind the midline. The anterior dorsal margin curves gently and the anterior margin is rounded. The posterior dorsal margin is straighter and the posterior margin is somewhat pointed. The periostracum is transparent and glossy and the shell is white with tinges of yellow or brown. There is a sculpture of fine concentric lines on both valves and some faint radial ribs on the right valve only. The inner surface of the valves is white, sometimes tinted with yellow or orange. The mantle is white with a fringe of tentacles and the gills are unequal in size.

Distribution

''F. fabula'' occurs off the coasts of north west Europe and Morocco and in the Mediterranean Sea and the Black Sea. It is found from low water level to a depth of about forty metres. In a study off the Belgian coast in 2006, this species was found at a maximum density of over a thousand individuals per square metre.

Biology

''Fabulina fabula'' burrows in clean or slightly muddy sand and has a large foot and two long siphons which it extends to the surface of the sediment. The longer siphon gropes around for organic debris to draw down to the body, while the other is used to expel water.Barrett, J. H. and C. M. Yonge, 1958. Collins Pocket Guide to the Sea Shore. P. 161. Collins, London ''F. fabula'' is both a deposit and a filter feeder.Salzwedel, H., 1979. Reproduction, growth, mortality and variations in abundance and biomass of ''Tellina fabula'' (Bivalvia) in the German Bight in 1975/1976. Veroffentlichungen des Instituts fur Meeresforschung in Bremerhaven, 18, 111-202. Individual molluscs are either male or female and

gamete A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce ...

s are liberated into the

water table The water table is the upper surface of the zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with water. It can also be simply explained as the depth below which the ground is saturated. T ...

during spring and summer. The

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. ...

e are free swimming and form part of the

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 ...

for from 11 to 30 days. Maturity is reached at a size of about 10 millimetres after 1 to 2 years, and the lifespan is up to 5 years.

Ecology

The closely related species, ''

Tellina tenuis ''Tellina tenuis'', the thin tellin, is a species of marine bivalve mollusc in the family Tellinidae. It is found off the coasts of northwest Europe and in the Mediterranean Sea, where it lives buried in sandy sediments. Bivalves are molluscs ...

'' is found over the same distribution range but the two are not usually in competition as ''T. tenuis'' occurs from the middle shore level to a depth of about seven metres. In the sandy sea bed that it favours, ''F. fabula'' is often found in association with the sea potato, ''

Echinocardium cordatum ''Echinocardium cordatum'', also known as the common heart urchin or the sea potato, is a sea urchin in the family (biology), family Loveniidae. It is found in sub-tidal regions in the NE Atlantic. Other un-named species have been identified as t ...

'', and the bivalve

molluscs 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 estim ...

Ensis ensis ''Ensis ensis'', or the sword razor, is a razor clam, a marine bivalve mollusc in the family Pharidae. It lives buried in the sand and is found off the coasts of northwest Europe. Description The two valves that make up the shell of ''Ensis ...

'' and ''

Chamelea gallina ''Chamelea gallina'' is a species of small saltwater clam, a marine bivalve in the family Veneridae, the venus clams. Taxonomy Carl Linnaeus originally described ''Venus gallina'' from the Mediterranean Sea in 1758. It was not clear whether d ...

''.Elements of Marine Ecology
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References

{{Taxonbar, from1=Q61681104, from2=Q3016263 Tellinidae Bivalves described in 1791 Taxa named by Johann Friedrich Gmelin