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| − | {{honor_header|3|1949|Nature|General Conference}}
| + | [[Image:Viviparus contectus met operculum2.JPG|right|thumb|[[Gastropod shell]] of ''[[Viviparus contectus]]'' with operculum]] |
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| − | ==1. Have the Shell Honor. ==
| + | The '''operculum''', meaning little lid, (plural: opercula or operculums) is a corneous or [[calcareous]] structure which exists in some groups of marine, freshwater, and land [[snail]]s or [[gastropod]]s. It is present in most but not all gastropods that have shells and gills. [[Pulmonate]] snails do not have have opercula, but some [[terrestrial]] species are capable of secreting an epiphragm, see below. |
| − | {{Ay prerequisite|Nature|Shells}}
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| − | ==2. Define the term "mollusca" or "mollusk." ==
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| − | The word ''mollusc'' is derived from the French ''mollusque'', which originated from the Latin ''molluscus'', meaning thin-shelled, from ''mollis'', soft | |
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| − | The body of a mollusk consists of three sections; a head, with eyes or tentacles; a muscular foot; and a visceral mass housing the organs.
| + | In its most typical condition, an operculum serves to close the opening or [[aperture (mollusc)|aperture]] of the [[gastropod shell|shell]] when the soft parts of the animal are withdrawn into the shell. |
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| − | ==3. Learn the classification terms of mollusks, know the distinguishing characteristics of each, and become acquainted with several species under each class. ==
| + | An operculum can vary in shape greatly from one family of gastropods to another, but an operculum is fairly often circular, or more or less oval in shape. In species where the operculum fits snugly, its outline corresponds exactly to the shape of the [[aperture (mollusc)|aperture]] of the shell. |
| − | There are ten classes of molluscs; eight of the classes have living representatives, the other two classes are known only from fossils. More than 250,000 species of mollusc are recognized and named. Snails (Gastropoda) account for about 80% of living mollusc diversity.
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| − | <center>
| + | ==Functions== |
| − | {| border=1 cellpadding=5
| + | Perhaps the most essential function of the operculum is to allow snails to resist drying out, or [[desiccation]]. This is very important in intertidal marine snails during low tide, and this also enables operculate pond and land snails to survive periods of drought and periods of dry weather. |
| − | |width="110" | '''Class'''
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| − | |width="300" | '''Major organisms'''
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| − | |width="120" | '''Extant species'''
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| − | |width="120" | '''Distribution'''
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| − | | Caudofoveata || worm-like organisms || 70 || deep ocean
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| − | | Aplacophora || solenogasters, worm-like organisms || 250 || deep ocean
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| − | | Polyplacophora || chitons || 600 || rocky marine shorelines
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| − | | Monoplacophora || limpet-like organisms || 11 || deep ocean
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| − | | Gastropoda || abalone, limpets, conch, nudibranchs, sea hares, sea butterfly, snails, slugs || 150,000<ref>Ponder, Winston F. and Lindberg, David R. (Eds.) (2008) [http://www.ucpress.edu/books/pages/10802.php ''Phylogeny and Evolution of the Mollusca'']. Berkeley: University of California Press. 481 pp. ISBN 978-0520250925.</ref> || marine, freshwater, land
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| − | | Cephalopoda || squid, octopus, cuttlefish, nautilus || 786 || marine
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| − | | Bivalvia || clams, oysters, scallops, mussels || 8000 || marine, freshwater
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| − | | Scaphopoda || tusk shells || 350 || marine
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| − | | Rostroconchia † || fossils; probable ancestors of bivalves || extinct || —
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| − | | Helcionelloida † || fossils; snail-like organisms such as ''Latouchella'' || extinct || —
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| − | |}
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| − | </center>
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| − | ==4 Distinguish between univalve and bivalve mollusks from the following considerations: ==
| + | In those species where the operculum completely seals the shell, it can also serve as a protection against [[predator]]s when the snail body is retracted. |
| − | ===a. Shell ===
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| − | The terms ''univalve'' and ''bivalve'' refer to the configuration of the shells of the mollusks. Univalves, such as snails, have shells consisting of one (thus ''uni-'') piece. Bivalves, such as mussels, have shells consisting of two (thus ''bi-'') pieces hinged together.
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| − | ===b. Mollusk body === | + | ==Anatomy== |
| − | ;Univalves: Univalve bodies could almost be described as ''folded'' such that the mouth and anus both appear the the shell's opening.
| + | In life, the operculum is attached dorsally to the upper surface of the posterior part of the foot, where it grows in size as the shell grows, such that the operculum remains in proportion to the apertural size. In many species, when the animal is active and crawling, part of the underside of the shell rests on the outer surface of the operculum. |
| − | ;Bivalves: Bivalves on the other hand, have flattened bodies.
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| − | ===c. Reproduction===
| + | In many species of marine shelled snails which live subtidally, the operculum is greatly reduced in size, and no longer serves to seal the shell entrance. In some families it has been eliminated. |
| − | ;Univalves: All land snails are hermaphrodites, producing both spermatozoa and ova. In other words, each individual is both male and female. Some freshwater snails, such as Apple Snails, and marine species, such as periwinkles, have separate sexes; they are male and female. Most snails can mate when they are around 1 year old.
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| − | :Prior to reproduction, most land snails perform a ritual courtship before mating. This may last anywhere between two and twelve hours. Prolific breeders, pulmonate land snails inseminate each other in pairs to internally fertilize their ova. Each brood may consist of up to 100 eggs.
| + | In species of [[conch]]es, the operculum is elongated and claw-shaped, and is used to dig into the sand to enable the conch to perform a leaping type of [[locomotion]]. |
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| − | :Pulmonate land snails and slugs have a reproductive opening on one side of the body, near the front, through which the outer reproductive organs are extruded so that exchange of sperm can take place. After this, fertilization occurs and the eggs develop.
| + | The operculum has a concentric structure. The nucleus is central in some genera, and in other the nucleus is near the parietal margin of the shell. |
| | | | |
| − | :Garden snails bury their eggs in shallow topsoil primarily while the weather is warm and damp, usually 5 to 10 cm down, digging with their foot. Egg sizes differ between species, from a 3 mm diameter in the grove snail to a 6 cm diameter in the Giant African Land Snail. After 2 to 4 weeks of favorable weather, these eggs hatch and the young emerge. Snails may lay eggs as often as once a month.
| + | There are two basic types of opercula in terms of their material composition: |
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| − | ;Bivalves: In bivalves, the sexes are usually separate, but some hermaphroditism is known. Bivalves practice external fertilization. External fertilization is a form of fertilization in which a zilo cell is united with an egg cell external to the body of the female. Thus, the fertilization is said to occur "externally". This is distinct from internal fertilization where the union of the egg and sperm occur inside the female after insemination through copulation.
| + | * The most common kind of operculum is composed of a thin to rather thick corneous protein material, which is yellow to brownish in color and is usually somewhat translucent. This matter is supple when in its natural state but may become brittle when it is dried out. The operculum varies in shape, depending on the family of snails and the shape of the aperture of their shells. |
| | + | * The other kind of operculum is restricted to a few families of gastropods including the [[Turbinidae]]. This operculum structure has a corneous base with a heavy calcareous overlay. The calcareous surface in some genera has color or ornamentation of various kinds including, for example, pustules and incised grooves. |
| | + | Opercula may be described as multispiral (having many closely spaced spirals), [[wiktionary:paucispiral|paucispiral]] (with few spirals), and the different shapes of opercula can include ungulate (hooflike), claw-like, or ovate. The type and shape of the operculum is used to help identify and classify related groups (genera) of land operculates, and likewise some marine operculates. |
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| − | :In sexual reproduction, there must be some way of getting the sperm to the egg. Since sperm are designed to be mobile in a watery environment, aquatic mollusks can make use of the water in which they live. Eggs and sperm are simultaneously shed into the water, and the sperm swim through the water to fertilize the egg in a process known as broadcast fertilization.
| + | ==The epiphragm in shelled land pulmonate snails== |
| | + | Many species of shelled land [[Pulmonata|pulmonates]] can create an '''epiphragm''', which is a temporary structure used to seal off the aperture of the shell during [[estivation]] or [[hibernation]]. This is not an operculum, but it can serve some of the same functions. |
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| − | ===d. Movements===
| + | The epiphragm in numerous species is a simple membrane composed of dried mucus, but in a few others such as ''Helix pomatia'', it is a sturdy flat calcareous structure in which there is a small perforation, to allow for oxygen exchange. |
| − | [[Image:Snail climbing grass SMC 07.jpg|thumb|250px|right|Snail climbing a blade of grass]]
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| − | ;Univalves: Most snails move by gliding along on their muscular foot, which is lubricated with mucus. This motion is powered by succeeding waves of muscular contraction which move down the undersurface of the foot. This muscular action is clearly visible when a snail is crawling on the glass of a window or aquarium. Snails move at a proverbially low speed (1 mm/s is a typical speed for adult ''Helix lucorum''). They produce mucus in order to aid locomotion by reducing friction, and the mucus also helps reduce the snail's risk of mechanical injury from sharp objects. This means that they can 'walk' over sharp objects like razors without being injured.
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| − | ;Bivalves: Razor shells (''Ensis spp.'') can dig themselves into the sand with great speed to escape predation. Scallops can swim to escape an enemy, clapping their valves together to create a jet of water. Cockles can use their foot to leap from danger. However these methods can quickly exhaust the animal. In the razor shells the siphons can break off only to grow back later.
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| − | {{clear}}
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| − | ===e. Securing food===
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| − | ;Bivalves: Bivalves are unique among the molluscs for lacking a radula; they feed by siphoning and filtering large particles from water.
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| − | ;Univalves: Univalves include some that are herbivores, detritus feeders, predatory carnivores, scavengers, parasites, and also a few ciliary feeders, in which the radula is reduced or absent. The radula of a univalve is usually adapted to the food that a species eats. The simplest univalves are the limpets and abalones, herbivores that use their hard radulas to rasp at seaweeds on rocks. Many marine univalves are burrowers, and have soft siphons or tubes that extend from the mantle. Sometimes the shell has a siphonal canal to accommodate this structure. A siphon enables the animal to draw a small flow of water into their bodies. The siphon is used primarily to "taste" the water, in order to detect prey from a distance. Univalves with siphons tend to be either predators or scavengers.
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| − | ===f. Self-preservation===
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| − | ;Univalves: When retracted into their shells, many snails with gills (including many marine, some freshwater and some terrestrial species) are able to protect themselves with a door-like anatomical structure called an operculum. Some snails hibernate during the winter (typically October through April in the Northern Hemisphere). They may also estivate in the summer in drought conditions. To stay moist during hibernation, a snail seals its shell opening with a dry layer of mucus called an epiphragm.
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| − | ;Bivalves: The radical structure of the bivalves affects their behaviour in several ways. the most significant is the use of the closely-fitting valves as a defence against predation and, in intertidal species such as mussels, drying out. The entire animal can be contained within the shell, which is held shut by the powerful adductor muscles. This defence is difficult to overcome except by specialist predators such as the Starfish and Oystercatcher. The file shells (''Limidae'') can produce a noxious secretion when threatened, and the fan shells of the same family have a unique, acid-producing organ.
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| − | ==5. Identify from shells or drawings and know the meaning of the following concho logical terms: ==
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| − | ===a. Valve ===
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| − | ===b. Apex ===
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| − | The apex is a word most often used to mean the tip of the spire of the shell of a gastropod. It is the first-formed, and therefore the oldest, part of the shell. To be more precise, the apex would usually be where the tip of the embryonic shell or protoconch is situated, if that is still present in the adult shell.
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| − | The word apex can also be used to refer to a similar part in other molluscan shells, however, the apex of bivalves is more usually known as the umbos, beaks or prodissoconch.
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| − | The apex of tusk shells is the small, open posterior end, and the opening itself is usually called the apical aperture.
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| − | The phrase apical whorls, or protoconch, means the whorls of the embryonic shell at the apex of the shell, especially when this is clearly distinguishable from the later whorls of the shell, otherwise known as the teleoconch.
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| − | The space under the apex of a patellate gastropod is called the apical cavity.
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| − | ===c. Aperture ===
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| − | [[Image:Semicassis pyrum (base).JPG|thumb|250px|''Semicassis pyrum'', which has a large aperture.]]
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| − | The aperture is the main (or only) opening in the shell of a gastropod or snail. It is where the soft parts of the animal emerge. In some prosobranch gastropods, the aperture is able to be closed, and even completely sealed, with a sort of door or operculum.
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| − | The aperture of many snail shells is round, rounded, elliptical or oval. This shape corresponds roughly to the cross-section of the body whorl of the shell.
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| − | The aperture of a snail shell can have many other forms: semicircular, trilobate or auriculate. In some gastropods, the aperture is narrowed by protruding shell folds or "bacon", which help make the soft parts of the animal less vulnerable to predation.
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| − | For convenience of reference, the apertural edge or margin of a gastropod shell is divided into three areas or walls:
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| − | * The parietal wall: the area next to the penultimate whorl of the shell
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| − | * The columellar wall: the wall next to the columella
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| − | * The palatal wall: the outer free wall of the final whorl of the shell
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| − |
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| − | ===d. Byssus ===
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| − | [[Image:Zebra mussel GLERL 1.jpg|left|thumb|byssus threads on ''Dreissena polymorpha'']]
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| − | Mussels use byssus to attach to rocks and other surfaces. When a mussel's foot encounters a crevice, it creates a vacuum chamber by forcing out the air and arching up, similar to a plumber's plunger unclogging a drain. The byssus, made of keratin and other proteins, is spewed into this chamber, and bubbles into a sticky foam. By curling its foot into a tube and pumping the foam, the mussel produces sticky threads about the size of a human hair. It varnishes the threads with another protein, resulting in an adhesive.
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| − | Byssus is a remarkable adhesive that is neither degraded nor deformed by water as are synthetic adhesives. This has spurred genetic engineers to insert mussel DNA into yeast cells for translating the genes into the appropriate proteins.
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| − | ===e. Foot ===
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| − | ===f. Mantle ===
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| − | [[Image:Loligo vulgaris.jpg|250px|thumb|European Squid (''Loligo vulgaris''). The mantle is all that is visible behind the head.]]
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| − | The mantle is an important part of the anatomy of molluscs. It is the dorsal body wall which covers the visceral mass.
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| − | In many, but by no means all, species of molluscs, the epidermis of the mantle secretes calcium carbonate and creates a shell.
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| − | The word "mantle" (a old word, meaning cloak) is used for this anatomical structure because in many kinds of molluscs, the edge of the mantle extends beyond the main part of the body, forming flaps or double-folded structures.
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| − | {{clear}}
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| − | ===g. Operculum===
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| − | ===h. Mother of pearl===
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| − | ===i. Epidermis===
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| − | ===j. Ribs===
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| − | ===k. Teeth===
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| − | ===l. Concentric lines===
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| − | ===m. Canal===
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| − | ===n. Spines===
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| − | ===o. Whorls===
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| − | ===p. Lips===
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| − | ==6. Explain the development of a shell. How long do mollusks live?==
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| − | <gallery perrow=3 widths=200>
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| − | Image:Cypraea chinensis with partially extended mantle.jpg|The marine gastropod ''Cypraea chinensis'', the Chinese Cowry, showing partially extended mantle
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| − | Image:Giant_clam_or_Tridacna_gigas.jpg|The giant clam (''Tridacna gigas'') is the largest extant bivalve
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| − | Image:A fossil shell with calcite.jpg|Fossil shell covered in calcite crystals
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| − | </gallery>
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| − | In those mollusks which have a shell, the shell grows gradually over the lifetime of the mollusc by the addition of calcium carbonate to the leading edge or opening, and thus the shell gradually becomes longer and wider, in an increasing spiral shape, to better accommodate the growing animal inside. The animal also thickens the shell as it grows, so that the shell stays proportionately strong for its size.
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| − | A mollusk shell is formed, repaired and maintained by a part of the anatomy called the mantle. Any injuries to or abnormal conditions of the mantle are usually reflected in the shape and form and even color of the shell. When the animal encounters harsh conditions which limit its food supply, or otherwise cause it to become dormant for a while, the mantle often ceases to produce the shell substance. When conditions improve again and the mantle resumes its task, a "growth line" which extends the entire length of the shell is produced, and the pattern and even the colors on the shell after these dormant periods are sometimes quite different from previous colors and patterns.
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| − | Interestingly, within some species of mollusk there is often a surprising degree of variation in the exact shape, pattern, ornamentation, and color of the shell.
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| − | The longest lived mollusk is the ''Arctica islandica'' (Ocean Quahog). Animals of this species close to 400 years old are not uncommon.
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| − | ==7. Give some facts about the life of a strombus pugilis (fighting conch) and explain why this shell is so named. ==
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| − | ==8. Explain the activities of the shipworm. ==
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| − | {{:Adventist Youth Honors Answer Book/Nature/Shipworm}}
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| − | ==9. What accounts for the distribution of mollusks.==
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| − | ==10. Name two mollusks that have no shells. ==
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| | <gallery> | | <gallery> |
| − | Image:Unknown slug on rhubarb.jpg|<center>Slug</center> | + | Image:Helix pomatia operculum hg.jpg|''[[Helix pomatia]]'' with the calcareous epiphragm in place |
| − | Image:Octopus in sea life Helsinki.jpg|<center>Octopus</center>
| + | Image:Helix pomatia - epiphragma.jpg|The epiphragm of ''Helix pomatia'', a view of the inner surface, left, and the outer surface, right |
| − | Image:Cuttlefish.jpg|<center>Cuttlefish</center>
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| − | Image:Mastigoteuthis flammea.jpg|<center>Squid</center> | |
| | </gallery> | | </gallery> |
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| − | ==11. Find answers for the following interesting questions: == | + | ==Human use== |
| − | ===a. How are bivalve and univalve animals fastened to their shells? === | + | ===As incense material===<!-- This section is linked from [[Incense]] --> |
| − | ===b. How is shell color controlled? ===
| + | Operculum of certain [[gastropods]], especially varieties from the [[Red Sea]], has long served as an [[incense]] material in ancient [[Jew]]ish tradition, as well as in [[Christian]] and [[Arabian]] [[Muslim]] faiths. The operculum of conch species ''[[Strombus|Strombus tricornis]]'' and ''[[conch | Lambis truncata sebae]]'' are most commonly used in regions near the [[middle east]]. Opercula from these conches may be the "'''Onycha'''" incense material which is described in the Book of [[Exodus]]. |
| − | [[Image:Nautilus profile.jpg|thumb|300px|The Nautilus, a mollusk with four gills]] | |
| − | ===c. What mollusk has four gills? ===
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| − | The '''Nautilus'' has two pairs of gills (that's four!).
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| − | ===d. From what sea animal was India ink formerly made? ===
| + | Operculum powder is also an important ingredient in [[China|Chinese]] and [[Japan]]ese incense making. Here it is 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 other maine [[snail]]s, including those found Southeast Asia, South America, and East Africa. Operculum is traditionally treated with [[vinegar]], [[alcohol]] and [[water]] in order to remove any [[fish]]y smell. The clean opercula are then ground to a powder and used as a scent fixative, in a similar technique to that used in [[perfume]]s with certain plant [[resin]]s. |
| − | Cuttlefish have ink, like squid and octopuses. This ink was formerly an important dye, called sepia. Today artificial dyes have replaced natural sepia.
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| − | ===e. What mollusk spins a silken thread? ===
| + | When burnt on its own, high quality operculum reportedly smells of [[castoreum]] or other animal [[musk]]s, while that of lower quality is reminiscent of burnt ''hair''. |
| − | Several mollusks spin a ''byssus'' which is used to anchor them to a substrate. These include mussels in the family ''Mytilidae'' and the zebra mussel (''Dreissena polymorpha''). However, the mollusk with perhaps the most extensive byssus is the '''rigid pen shell''' (''Atrina rigida''). Like most pen shells, ''A. rigida'' lives in soft bottoms, with the majority of the shell buried, point down, leaving only a few inches exposed, held in place by an extensive net of byssal threads.
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| − | ===f. What shells were used for money by ancient tribes? === | + | ===As a gemstone=== |
| − | Many people find the very rounded, shiny, porcelain-like shells of '''cowries''' pleasing to look at and to handle. Shells of certain species have historically been used as currency in several parts of the world, as well as being used, in the past and present, very extensively in jewelry, and for other decorative and ceremonial purposes.
| + | The [http://www.manandmollusc.net/operculum_paul.html operculum] of certain species of [[Turbinidae]] is sometimes used as very inexpensive organic "[[gemstone]]" in rings, bracelets, amulets etc. These opercula are commonly known as "cats eye" (or more recently "Shiva's eye"). |
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| − | ===g. What shell is considered sacred by the Tibetans? ===
| + | The turban snail ''[[Turbo petholatus]]'' is the species whose operculum is most widely used, although the operculum of other species of ''Turbo'' are sometimes used. The operculum is almost always given a solid setting, because it has one unattractive flat and corneous side where it was attached to the animal, and one roughly hemispherical glossy side, which in the case of ''T. petholatus'' has an attractive dark green area. |
| − | Tibetan Buddhists make use of a particular set of eight auspicious symbols, ''ashtamangala'', in household and public art. The '''chank shell''' or '''conch''' is one of these eight symbols:
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| − | # Conch
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| − | # Knot
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| − | # Fish
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| − | # Banner
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| − | # Lotus
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| − | # Parasol
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| − | # Urn
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| − | # Wheel
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| − | ===h. Purple dye of ancient times came from the secretion of what mollusk? === | + | ==References== |
| − | ''Hexaplex trunculus'' (also known as ''Murex trunculus'' or the '''banded dye-murex''') is a medium-sized species of sea snail.
| + | *Burnie, D. (2001). ''[[Animal (book)|Animal: The Definitive Visual Guide to the World's Wildlife]]''. DK Adult Publishing. pg. 24. |
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| − | This species of sea snail is important historically because its hypobranchial gland secretes a mucus that the ancient Canaanites/Phoenicians used as a distinctive purple-blue indigo dye. One of the dye's main chemical ingredients is indigotin, and if left in the sun for a few minutes before becoming fast, its color turns to a blue indigo (like blue jeans).
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| − | ===i. What is the source of pearls? How are they formed? ===
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| − | Nacre, also known as mother of pearl, is an important part of the shell structure in many gastropod and bivalve mollusks especially the more ancient families such as top shells and pearl oysters. Like the other calcareous layers of the shell, the nacre is created by the epithelial cells (formed by the germ layer ectoderm) of the mantle tissue. Mollusk blood is rich in dissolved calcium, and during shell deposition, the calcium is concentrated out from the blood and crystallized as calcium carbonate. Nacre is continually deposited onto the inner surface of the animal's shell (the iridescent nacreous layer or mother of pearl). This is done both as a means to thicken, strengthen and smooth the inner surface of the shell itself and as a defense against parasitic organisms and damaging detritus.
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| − | When a mollusc is invaded by a parasite or is irritated by a foreign object that the animal cannot eject, a process known as encystation entombs the offending entity in successive, concentric layers of inner shell material, which in some cases is nacre. This process eventually forms what we call pearls and continues for as long as the mollusk lives. Almost any species of bivalve or gastropod is capable of producing "pearls", even mollusks which have no inner nacreous layer. However, only a few species, such as the famous pearl oysters, can create pearls which are highly prized.
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| − | ==12. Name six commercial uses for shells. == | + | ==External links== |
| − | ;Musical Instruments: Key touches and various decorations on musical instruments such as saxophones, trumpets, violins, banjos, tamburitzas and guitars are sometimes made of mother of pearl. It is used as inlays on many guitar fretboards.
| + | *[http://www.nansaidh.us/operc/index1.html 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 dozens of pictures of both the operculum and its host shell. |
| − | ;Clothing: Mother of pearl buttons can be found on a variety of clothing such as shirts, skirts and coats.
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| − | ;Decorative Inlays: Nacre is also used as a decorative feature of watch faces, knives, guns and jewelry.
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| − | ;Building Material: Instead of using a marble or tile base, the mother of pearl tesserae can be glued to a fiberglass mesh. The result is a lightweight material that offers a seamless installation, and there is no limit to the sheet size. Mother of pearl sheets may be used on interior floors, exterior and interior walls, countertops, doors and ceilings. Insertion into architectural elements, such as columns or furniture is easily accomplished. Conch shells are occasionally used as a building material, either in place of bricks or as bulk for landfill.
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| − | ;Jewelry: Pearls are highly prized jewelry components.
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| − | ;Souvenirs: In some countries, cleaned Queen Conch (''Strombus gigas'') shells or polished fragments are sold, mainly to tourists, as souvenirs or in jewelry. Without a permit, however, export is a breach of CITES regulations and may lead to arrest. This is most likely to occur on return to the tourist's home country while clearing customs. In the UK conch shells are the ninth most seized import.
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| − | ;Pets: Snails are often kept in aquariums along with fish.
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| | | | |
| − | ==13. Do one of the following: ==
| + | [[Category:Animal anatomy]] |
| − | ===a. Personally find and collect 40 species of shells representing the five classifications. List each shell as to the place and date it was found, common name, scientific name, and class. ===
| + | [[Category:Incense]] |
| − | ===b. Make a collection of 50 species of shells you have found, received, or purchased representing the five classifications. List each shell collected as follows: if personally found, give the information called for under letter "a" above; if received or purchased, give the name of the person from whom the shell was received, the habitat of the shell, the date of its acquisition, and its common name, scientific name, and class.===
| + | [[Category:Molluscs]] |
| − | ==References==
| |
| − | * http://depts.washington.edu/natmap/mollusks/glossary.html
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| − | * http://www.informaworld.com/smpp/content~content=a793157051~db=all~jumptype=rss
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| | | | |
| − | [[Category:Adventist Youth Honors Answer Book|{{SUBPAGENAME}}]] | + | [[cs:Operkulum]] |
| | + | [[de:Operculum]] |
| | + | [[eo:Operkulo]] |
| | + | [[fr:Opercule]] |
| | + | [[it:Opercolo]] |
| | + | [[nl:Operculum (plant)]] |
| | + | [[pt:Opérculo]] |
| | + | [[tl:Unya]] |
The operculum, meaning little lid, (plural: opercula or operculums) is a corneous or calcareous structure which exists in some groups of marine, freshwater, and land snails or gastropods. It is present in most but not all gastropods that have shells and gills. Pulmonate snails do not have have opercula, but some terrestrial species are capable of secreting an epiphragm, see below.
In its most typical condition, an operculum serves to close the opening or aperture of the shell when the soft parts of the animal are withdrawn into the shell.
An operculum can vary in shape greatly from one family of gastropods to another, but an operculum is fairly often circular, or more or less oval in shape. In species where the operculum fits snugly, its outline corresponds exactly to the shape of the aperture of the shell.
Functions
Perhaps the most essential function of the operculum is to allow snails to resist drying out, or desiccation. This is very important in intertidal marine snails during low tide, and this also enables operculate pond and land snails to survive periods of drought and periods of dry weather.
In those species where the operculum completely seals the shell, it can also serve as a protection against predators when the snail body is retracted.
Anatomy
In life, the operculum is attached dorsally to the upper surface of the posterior part of the foot, where it grows in size as the shell grows, such that the operculum remains in proportion to the apertural size. In many species, when the animal is active and crawling, part of the underside of the shell rests on the outer surface of the operculum.
In many species of marine shelled snails which live subtidally, the operculum is greatly reduced in size, and no longer serves to seal the shell entrance. In some families it has been eliminated.
In species of conches, the operculum is elongated and claw-shaped, and is used to dig into the sand to enable the conch to perform a leaping type of locomotion.
The operculum has a concentric structure. The nucleus is central in some genera, and in other the nucleus is near the parietal margin of the shell.
There are two basic types of opercula in terms of their material composition:
- The most common kind of operculum is composed of a thin to rather thick corneous protein material, which is yellow to brownish in color and is usually somewhat translucent. This matter is supple when in its natural state but may become brittle when it is dried out. The operculum varies in shape, depending on the family of snails and the shape of the aperture of their shells.
- The other kind of operculum is restricted to a few families of gastropods including the Turbinidae. This operculum structure has a corneous base with a heavy calcareous overlay. The calcareous surface in some genera has color or ornamentation of various kinds including, for example, pustules and incised grooves.
Opercula may be described as multispiral (having many closely spaced spirals), paucispiral (with few spirals), and the different shapes of opercula can include ungulate (hooflike), claw-like, or ovate. The type and shape of the operculum is used to help identify and classify related groups (genera) of land operculates, and likewise some marine operculates.
The epiphragm in shelled land pulmonate snails
Many species of shelled land pulmonates can create an epiphragm, which is a temporary structure used to seal off the aperture of the shell during estivation or hibernation. This is not an operculum, but it can serve some of the same functions.
The epiphragm in numerous species is a simple membrane composed of dried mucus, but in a few others such as Helix pomatia, it is a sturdy flat calcareous structure in which there is a small perforation, to allow for oxygen exchange.
The epiphragm of Helix pomatia, a view of the inner surface, left, and the outer surface, right
Human 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. Opercula from these conches may be the "Onycha" incense material which is described in the Book of Exodus.
Operculum powder is also an important ingredient in Chinese and Japanese incense making. Here it is 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 other maine snails, including those found Southeast Asia, South America, and East Africa. Operculum is traditionally treated with vinegar, alcohol and water in order to remove any fishy smell. The clean opercula are then 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.
As a gemstone
The operculum of certain species of Turbinidae is sometimes used as very inexpensive organic "gemstone" in rings, bracelets, amulets etc. These opercula are commonly known as "cats eye" (or more recently "Shiva's eye").
The turban snail Turbo petholatus is the species whose operculum is most widely used, although the operculum of other species of Turbo are sometimes used. The operculum is almost always given a solid setting, because it has one unattractive flat and corneous side where it was attached to the animal, and one roughly hemispherical glossy side, which in the case of T. petholatus has an attractive dark green area.
References
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 dozens of pictures of both the operculum and its host shell.
cs:Operkulum
de:Operculum
eo:Operkulo
fr:Opercule
it:Opercolo
nl:Operculum (plant)
pt:Opérculo
tl:Unya
