''Saccostrea cucullata'', the hooded oyster or Natal rock oyster, is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of rock oyster found mainly in the Indo-Pacific Ocean. It was first described by the Czech mineralogist, metallurgist, and malacologist

Ignaz von Born Ignaz Edler von Born, also known as Ignatius von Born ( hu, Born Ignác, ro, Ignațiu von Born, cs, Ignác Born) (26 December 1742 in Alba Iulia, Grand Principality of Transylvania, Habsburg monarchy – 24 July 1791 in Vienna), was a miner ...

in 1778.

Description

The appearance and form of the hooded oyster is very variable. The shape is sometimes nearly circular or it may be oblong or roughly oval, often with an irregular outline. In the Mediterranean, it grows to , but achieves double that size in the Pacific Ocean. The valves are thick and solid. The lower valve is convex and has no sculpturing near the umbo, which is fixed to the substrate. The upper valve is flat and smaller than the lower valve. It may have wide, sometimes spiny, ribs but is sometimes quite smooth. The margins of the valves are pleated and fit together neatly. The ligament is internal and no teeth occur on the hinge joint. The right valve has some small denticles on its margin which fit into grooves in the left valve margin. A single large adductor muscle holds the valves together, resulting in a large, kidney-shaped scar on the inside of each valve. The colour is purplish-brown on the outside of the valves. The inside is white rimmed with black. This oyster could be confused with the

Pacific oyster The Pacific oyster, Japanese oyster, or Miyagi oyster (''Magallana gigas''), is an oyster native to the Pacific coast of Asia. It has become an introduced species in North America, Australia, Europe, and New Zealand. Etymology The genus ''Mag ...

(''Crassostrea gigas''), but is distinguished by having a crenulated margin.

Distribution and habitat

The hooded oyster is found in the Indian Ocean and tropical west Pacific Ocean. In East Africa, its range includes Somalia, Kenya, Tanzania, and the Seychelles. In India, it is one of a number of commercially exploited oyster species. It is also found in Australia, New Zealand, and the Red Sea. It was first seen in Turkey in 1999 and seems to have become established in the eastern end of the Mediterranean. It favours rocky habitats in the intertidal zone, and is found at depths down to about , often growing among seaweed. It is part of the fouling community and is found on harbour walls, pilings, and other underwater structures.

Biology

The hooded oyster is a filter feeder, pumping water through its gills and removing the phytoplankton. In polluted waters, it accumulates heavy metals in its tissues. For this reason it can be used as a

bioindicator A bioindicator is any species (an indicator species) or group of species whose function, population, or status can reveal the qualitative status of the environment. The most common indicator species are animals. For example, copepods and other sma ...

for monitoring pollution. Because it selectively removes these metals and is such an efficient biofilter, it has been used in the Persian Gulf to control pollution. The hooded oyster is tolerant of a wide range of temperatures and salinities. Breeding takes place between June and October in the Northern Hemisphere. The larvae are

plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a crucia ...

ic and preferentially settle out of the

water column A water column is a conceptual column of water from the surface of a sea, river or lake to the bottom sediment.Munson, B.H., Axler, R., Hagley C., Host G., Merrick G., Richards C. (2004).Glossary. ''Water on the Web''. University of Minnesota-D ...

in locations already occupied by adult oysters.

Ecology

The hooded oyster is common on the east coast of Africa, where it cements itself to rocks or to the branches and roots of

mangrove A mangrove is a shrub or tree that grows in coastal saline or brackish water. The term is also used for tropical coastal vegetation consisting of such species. Mangroves are taxonomically diverse, as a result of convergent evolution in severa ...

s. It sometimes even grows on the shell of a large gastropod mollusc, the mangrove whelk (''

Terebralia palustris ''Terebralia palustris'', common name the giant mangrove whelk, is a species of brackish-water snail, a gastropod mollusk in the family Potamididae. This tropical species which inhabits mangrove environments of the Indo-West Pacific region,Houbr ...

''), which grazes beneath the mangrove canopy. In Australia, another gastropod, the black oyster borer or mulberry whelk ('' Tenguella marginalba'', previously ''Morula marginalba'') feeds on the oyster by drilling a hole through its shell. It then inserts its radula and chews up the body before sucking out the pieces.

References

External links

Plate LI
shows fossil specimens of ''S. saccellus'' (later synonymized with ''S. cuccullata'') compared to a shell of ''

Ostrea edulis ''Ostrea edulis'', commonly known as the European flat oyster, is a species of oyster native to Europe. In Britain and Ireland, regional names include Colchester native oyster, mud oyster, or edible oyster. In France, ''Ostrea edulis'' are known ...

''. In Tome XXII (1920) of ''Memoire no. 27, Conchyliologie du Miogène moyen du Bassin de la Loire'' by G.-F. Dollfus and Ph. Dautzenberg. {{Commons category cucullata Bivalves described in 1778