Operculum (gastropod)

An operculum (Latin for " little top ", Pl. opercula ) is a horny or calcareous cap worn by the worm from the group of prosobranch at the top of her foot. For the mouth of the case is closed when the animal has withdrawn to rest (about the drying out of the water ) or at risk of it. The largest and best known prosobranch of European inland waters, the river snails ( Viviparidae ), wear this cap even in the name of Germany. Similarly, the terrestrial land snails ( Pomatiidae ), to which the indigenous Beautiful land snail ( Pomatias elegans ) is one.

The operculum is not to be confused with the fixed Epiphragma, with some snails close their case, and even with the clausilium featuring the lung worm family of door snails ( Clausiliidae ).

The operculum has concentric structures and has a core near the mouth of the wall of the housing ( close to the navel) facing edge. There are two types of opercula:

• The first type consists of Horny material of different thickness. The substance is flexible and layered, and the operculum is more or less circular.
• The second type ( referred to as " shutter stone " ) has a multilayer structure, with horny and calcareous base coating layer, which is sometimes sculptured with helical structures, and grooves. This lime is a crystallized with particular structural form of aragonite. Just as with real pearls this is a calcium carbonate ( CaCO3), which has a hardness of 4 to 4.5 on the Mohs scale. After the death of the operculum detaches from the shell and can be found on the beach and in shallow water.

Use

The use of snail shell lids can be detected from the Stone Age beginning to the present day. The opercula appear in a different context in different cultures.

Jewelery and object collection

The nearly hemispherical, colored opercula of turban snails ( Turbinidae ) are a popular collector's item and are also processed into jewelry. They all have the flat, white underside ( the retracted snail inward facing side) a typical spiral growth pattern on, occasionally delicious fresh finds still brownish remnants of the stratum corneum to. The color and quality of the outwardly facing arch of the really white aragonite is by pigments of Algenteilchen in food intake especially in the absence of / increase, but especially when changing ( local, seasonal and environmental depend on other factors ) of algae types (especially determined at the cat's eye worm).

Some snail species

When ribbed turban snail Turbo petholatus (up to 6 cm high) of almost hemispherical closure stone in the outer area is mostly white to light brown and deepens the color to the center, sometimes to brown - black. Diameter of the finds approximately 2.6 cm of the semimajor axis.

The rare cat's eye snail Turbo radiatus (up to 8 cm high ), however, provides a common oval operculum, which is often a slightly spiral, radiating gradient is in the center, is often deeply colored dark blue-green, and therefore as a " cat's eye " rare "Tiger Eye", renamed. Diameter of the finds approximately 3.0 cm of the semimajor axis.

The operculum of conch Charonia tritonis is on the top and bottom of dazzling white to beige. The maximum diameter of the largest semi-axis of the discovery of 10 cm it belongs in the heavyweight division and is for these reasons uninteresting for jewelery production.

Jewelry and collectibles

In some parts of the world, the opercula are known under trade names in the jewelry industry. In coastal areas of Papua and on remote islands of the South Seas with native tribes are still regarded as particularly fine examples (now increasingly rare ) ritual be revised in the jewelery symbol and social status object. Special stones are here ( also slacking ) as monetary values ​​or similar equipment in issue or serve the interpersonal advertising in the form of jewelry stones.

Finds are usually through cracks and small holes (probably spiral tube worms ) damaged. The intact and extra large opercula usually stay local collectors ( the associated screws are popular seafood), snorkelers and divers reserved. A special collector's value set stones represent herumverläuft whose spiral to the left, so a different " handedness " has (see also quite related explanation for the chemical chirality ); the ratio is, for example, in the body of the snail 1:20,000. The irregular food intake or change in the type of algae, some Operculae on coveted, unusual gradients. The cover is ground in some tourist areas to semi-precious stones for ear rings, finger rings and necklaces in the form of the text, most slightly polished, processed rare painted.

Incense

Opercula of certain snails, especially species from the Red Sea ( particularly Strombus tricornis and lambis truncata sebae ) may be used from time immemorial as incense, according to Jewish as well as Christian and Muslim tradition. It is believed that it was this snail opercula in the described in the second book of Moses incense Onycha.

Powdered opercula are also referred to an important part of East Asian incense in China as Beixiang (贝 香, literally "Shell fragrance" ) and in Japan as Kaiko (甲 香, literally " shell " or "Panzer fragrance" ). Opercula traditionally treated with ethyl alcohol and water to remove any smell of fish, and then ground and used as Duftfixativ similar perfume.

Burned alone, to quality Operculumpulver as castoreum or certain animal musks smell, inferior, however, like burnt hair.