Operculum
An operculum ( Latin for "little lid", Pl. Opercula) is a horny or chalky lid that snails from the group of forelegs wear on the top of their feet. This closes the mouth of the housing when the animal has withdrawn to rest (e.g. when the water dries out) or when it is in danger. The largest and best-known foreleg gills of the European inland waters, the marsh snails (Viviparidae), even have this lid in their German name. Likewise the land-living land snail (Pomatiidae), to which the native beautiful land snail ( Pomatias elegans ) belongs.
The operculum is not to be confused with the fixed epiphragma with which some lung snails close their shell, and also not with the clausilium , which characterizes the lung snail family of door snails (Clausiliidae).
The operculum has concentric structures and has a core near the edge facing the mouth wall of the housing (close to the navel). There are two types of opercula:
- The first type is made of horny material of various thicknesses. The substance is pliable and monolayer, and the operculum is more or less circular.
- The second type (also referred to as "locking stone") has a multilayered structure, with a horny base and a calcareous top layer, which is sometimes sculpted with spiral structures and grooves.
This lime is a form of aragonite that has crystallized out with a special structure . Just like real pearls , this is a calcium carbonate (CaCO 3 ), which has a hardness of 4 to 4.5 on the Mohs scale . After death, the operculum detaches from the shell and can be found on the beach and in shallow water.
use
The use of snail shell covers can be traced from the Stone Age to the present. The opercula appear in different cultures in different contexts. The various names show the mystical attributions: sea umbilicus, sea eye, naxos eye, Oeil de Sainte Lucie, Shiva eye, Venus navel .
Jewelry and collection object
The almost hemispherical, colored opercula of the turban snails (Turbinidae) are a popular collector's item and are also made into jewelry. All of them show a typical spiral-shaped growth curve on the flat, white underside (the drawn-in snail facing inwards), occasionally fresh finds still adhere brownish remnants of the horny layer. The color and quality of the outward curvature of the actually white aragonite is determined by pigments from algae particles when eating, especially when there is no / increase, but especially when changing (depending on location, season and other environmental factors) of algae types (in particular in the cat's eye snail).
Some species of snail
In the ribbed turban snail Turbo petholatus (up to 6 cm high) the almost hemispherical locking stone is mostly white to light brown in the outer area and deepens the color towards the center, sometimes even brown-black. Diameter of the finds approx. 2.6 cm of the major semi-axis.
The rarer cat-eye snail Turbo radiatus (up to 8 cm high), on the other hand, provides an often oval operculum, which often shows a slightly spiral, radiant color gradient in the center, is often deeply dark blue-green, and is therefore known as "cat's eye", more rarely "tiger's eye" . The diameter of the finds approx. 3.0 cm along the major semi-axis.
The operculum of the conch Charonia tritonis is dazzling white to beige on the top and bottom. With the maximum diameter in the largest semi-axis of the find of 10 cm, it belongs to the heavyweight class and for these reasons is of no interest for making jewelry.
Jewelry industry and collectors
In some parts of the world the opercula are known by trade names in the jewelry industry. On sections of the coast of Papua and on remote islands of the South Seas with native tribes, particularly beautiful specimens are still considered to be a (now increasingly rare) ritual symbol incorporated into jewelry and a social status object. Special stones are here (also decreasing) as money-like values or investments in circulation or are used for interpersonal advertising in the form of gemstones.
Findings are usually damaged by cracks and small boreholes (probably tube worms ). The intact and particularly large opercula are usually reserved for local collectors (the associated snails are popular seafood ), snorkelers and divers. Stones with a counter-clockwise spiral are particularly valuable for collectors, ie with a different “handedness” (see also a related explanation of chemical chirality ); the ratio is z. B. in the case of the Roman snail 1: 20,000. Due to the irregular consumption of food or changes in the type of algae, some operculae show sought-after, unusual color gradients. In some tourist areas, the closure lid is processed into gemstones for earrings, finger rings and necklaces in the shape of the setting, at most slightly polished, less often lacquered.
Incense
Opercula of certain snails, especially species from the Red Sea (especially Strombus tricornis and Lambis truncata sebae ), have been used as incense since ancient times , according to Jewish as well as Christian and Muslim tradition. It is believed that this is where the second book of Moses described incense Onycha to opercula acted this worm.
Powdered opercula are also an important part of East Asian incense, known in China as bèixiāng (貝 香, literally "shell scent ") and in Japan as kaikō (甲 香, literally "shell" or "shell scent"). Traditionally, the opercula are treated with vinegar, alcohol and water to remove any fishy odor , and then ground and used as a scent fixative similar to perfumes .
Burned alone, high-quality operculum powder such as Bibergeil or certain animal musk species is said to smell, whereas inferior ones are said to smell like burned hair.
literature
- Georg Schifko: On the cultural history of snail shell covers (opercula) from an archaeological and ethnological point of view , in: Ethnographisch- Archäologische Zeitschrift , Berlin, EAZ, vol. 45.2004, 4, pp. 531-537
Web links
- Klaus Polak : Operculi, photos - especially for still undefined species
- Large selection of photos of around 40 different opercula with associated snail (English)