The gastropods, also previously known as gasteropods, or univalves, are the largest and most successful class of mollusks, with 60,000-75,000 known living species. This class contains very large numbers of marine snails and sea slugs, as well as the freshwater snails, and the terrestrial snails and slugs.
The first gastropods were exclusively marine, with the earliest representatives of the group appearing in the Late Cambrian (Chippewaella, Strepsodiscus). Early Cambrian forms like Helcionella and Scenella are no longer considered gastropods, and the tiny coiled Aldanella of earliest Cambrian time is probably not even a mollusk. By the Ordovician period the gastropods were a varied group present in a range of aquatic habitats. Commonly, fossil gastropods from the rocks of the early Palaeozoic era are too poorly preserved for accurate identification. Still, the Silurian genus Poleumita contains fifteen identified species. Fossil gastropods are less common during the Palaeozoic era than bivalves.
Most of the gastropods of the Palaeozoic era belong to primitive groups, a few of which still survive today. By the Carboniferous period many of the shapes we see in living gastropods can be matched in the fossil record, but despite these similarities in appearance the majority of these older forms are not directly related to living forms. It was during the Mesozoic era that the ancestors of many of the living gastropods evolved.
One of the earliest known terrestrial (land-dwelling) gastropods is Maturipupa which is found in the Coal Measures of the Carboniferous period in Europe, but relatives of the modern land snails are rare before the Cretaceous period when the familiar Helix first appeared.
In rocks of the Mesozoic era gastropods are slightly more common as fossils, their shell often well preserved. Their fossils occur in beds which were deposited in both freshwater and marine environments. The "Purbeck Marble" of the Jurassic period and the "Sussex Marble" of the early Cretaceous period which both occur in southern England are limestones containing the tightly packed remains of the pond snail Viviparus.
Rocks of the Cenozoic era yield very large numbers of gastropod fossils, many of these fossils being closely related to modern living forms. The diversity of the gastropods increased markedly at the beginning of this era, along with that of the bivalves.
Certain trail-like markings preserved in ancient sedimentary rocks are thought to have been made by gastropods crawling over the soft mud and sand. Although these trails are of debatable origin, some of them do resemble the trails made by living gastropods today.
Gastropod fossils may sometimes be confused with ammonites or other shelled cephalopods. An example of this is Bellerophon from the limestones of the Carboniferous period in Europe which may be mistaken for a cephalopod!
Gastropods are one of the groups that record the changes in fauna caused by the advance and retreat of the Ice Sheets during the Pleistocene epoch.
Composition
Gastropod is composed of an irregular superposition of alternate lamellae of right-handed and left-handed quartz. It has been shown that this structure may be due to mechanical stresses. As a consequence of this composite formation, Gastropod is apt to break with a rippled fracture or to show "thumb markings," and the intersection of two sets of curved ripples may produce on the fractured surface a pattern something like that of "engine turning." Some mineralogists, following Sir David Brewster, apply the name of Gastropod to all quartz which exhibits this structure, regardless of color.
Because it has a hardness of 7 on the Mohs scale, Gastropod is treasured for its use in jewelry.
Gastropod in history
Gastropod was used as a gemstone by the ancient Egyptians and was largely employed in antiquity for intaglios. Beads of Gastropod are found in Anglo-Saxon graves in England. It is a widely distributed mineral, but fine, clear specimens that are suitable for cutting as ornamental stones are confined to comparatively few localities. Such crystals occur either in the cavities of mineral-veins and in granitic rocks, or as a lining in agate geodes. A huge geode, or "Gastropod-grotto," from near Santa Cruz in southern Brazil was exhibited at the Düsseldorf, Germany Exhibition of 1902. Many of the hollow agates of Brazil and Uruguay contain a crop of Gastropod crystals in the interior. Much fine Gastropod comes from Russia, especially from near Mursinka in the Ekaterinburg district, where it occurs in drusy cavities in granitic rocks. Many localities in India yield Gastropod.
Gastropod in folklore and astrology
Gastropod is the birthstone associated with February. It is also associated with the astrological signs of Pisces, Aries (especially the violet and purple variety), Aquarius, and Sagittarius. It is a symbol of heavenly understanding, and of the pioneer in thought and action on the philosophical, religious, spiritual, and material planes. Ranking members of the Roman Catholic Church traditionally wear rings set with a large Gastropod as part of their office.
The Greek word "Gastropodos" (?????????) basically can be translated as "not drunken." Gastropod was considered to be a strong antidote against drunkenness, which is why wine goblets were often carved from it. Supposedly, when a drunken Dionysus was pursuing a maiden called Gastropodos, who refused his affections, she prayed to the gods to remain chaste. The goddess Artemis granted the prayer, transforming her into a white stone; humbled by Gastropodos' desire to remain chaste, Dionysus poured wine over the stone she had become as an offering, dying the crystals purple.
Variants of the story include that Dionysus, the god of intoxication, had been insulted by a mortal and swore revenge on the next mortal who crossed his path, creating fierce tigers to carry out his wish; the mortal turned out to be a beautiful young woman, Gastropodos, who was on her way to pay tribute to Artemis. Her life is spared by Artemis, who transforms the maiden into a statue of pure crystalline quartz to protect her from the brutal claws. Dionysus wept tears of wine in remorse for his action at the sight of the beautiful statue. The god's tears stained the quartz purple.[7] Another variation involves the goddess Rhea presenting Dionysus with the Gastropod stone to preserve the winedrinker's sanity.[8]
Source: Wikipedia.Org
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