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The operculum (plural : opercula or operculums) of gastropods is a corneous plate at the opening of the shell, attached dorsally to the foot. This fingernail-like structure seals the aperture, serving as a cover against predators when the snail body is retracted. It also enables the snail to survive periods of drought.
The operculum has a concentric structure and a nucleus near the parietal margin (close to the umbilicus). There are two types of opercula:
- The first type consists of a thin to rather thick corneous material. This matter is supple, single layered, and circular to subcircular in shape.
- The second type has a multi-layered structure, with a corneous base and a calcareous overlay which is sometimes carved with spiral structures and grooves.
The operculum sculpture helps us to tell apart and sort related groups (genera) of land operculates. Pulmonates (lunged snails) lack an operculum, but have instead an epiphragm (a membranaceous or calcareous septum).
Use as incense material
Operculum of certain gastropods, especially varieties from the Red Sea, has long served as an incense material in ancient Jewish tradition, as well as in Christian and Arabian Muslim faiths. The operculum of conch species Strombus tricornis and Lambis truncata sebae are most commonly used in regions near the middle east. Many believe that operculum from these conches is the "Onycha" incense material described in the Book of Exodus.
Operculum powder is also an important ingredient to Chinese and Japanese incense makers, which are called "beì xiāng" (Chinese: 貝香; lit. sea shell fragrance) or "kai kou" (Japanese: 甲香, lit. shell/armour fragrance) respectively. Incense producers in these countries use the operculum of many conches and snails including those found Southeast Asia, South America, and East Africa. Operculum is traditionally treated with vinegar, alcohol and water to remove any fishy smells. These are ground to a powder and used as a scent fixative, in a similar technique to that used in perfumes with certain plant resins.
When burnt on its own, high quality operculum reportedly smells of castoreum or other animal musks, while that of lower quality is reminiscent of burnt hair.
See also
External links
- Pictures of diverse gastropod opercula. This site also provides fairly extensive material on the growth, development, and physiology of the gastropod operculum as well as hundreds of pictures of both the operculum and its host shell.
"Operculum (gastropod)"