''Fabulina fabula'', the bean-like tellin, is a species 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 ...

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 ...

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 sedimen ...

. 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 respiration organ, respiratory organ that many aquatic ecosystem, 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 r ...

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 The periostracum ( ) is a thin, organic coating (or "skin") that is the outermost layer of the shell of many shelled animals, including molluscs and brachiopods. Among molluscs, it is primarily seen in snails and clams, i.e. in gastropods an ...

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 Filter feeders are aquatic animals that acquire nutrients by feeding on organic matters, food particles or smaller organisms (bacteria, microalgae and zooplanktons) suspended in water, typically by having the water pass over or through a s ...

.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 ( ) is a Ploidy#Haploid and monoploid, haploid cell that fuses with another haploid cell during fertilization in organisms that Sexual reproduction, reproduce sexually. Gametes are an organism's reproductive cells, also referred to as s ...

s are liberated into the

water table The water table is the upper surface of the phreatic zone or zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with groundwater, which may be fresh, saline, or brackish, depending on the loc ...

during spring and summer. The

larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

e are free swimming and form part of the

zooplankton Zooplankton are the heterotrophic component of the planktonic community (the " zoo-" prefix comes from ), having to consume other organisms to thrive. Plankton are aquatic organisms that are unable to swim effectively against currents. Consequent ...

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'' 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'', and the

molluscs 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 ...

'' Ensis ensis'' and ''

Chamelea gallina ''Chamelea gallina'' is a species of small saltwater clam, a marine Bivalvia, bivalve in the Family (biology), family Veneridae, the venus clams. Taxonomy Carl Linnaeus originally described ''Venus gallina'' from the Mediterranean Sea in 1758. ...

''.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