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More About Molluscs - Misc. ...
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The mollusks or molluscs are the large and diverse phylum Mollusca, which includes a variety of familiar creatures well-known for their decorative shells or as seafood. These range from tiny snails and clams to the octopus and squid (which are considered the most intelligent invertebrates). The giant squid is the largest invertebrate, and, except for their larvae and some recently captured juveniles, has never been observed alive, although the Colossal Squid is likely to be even larger.
Mollusks are triploblastic protostomes. The principal body cavity is a blood-filled hemocoel, with an actual coelom present but reduced to vestiges around the hearts, gonads, and metanephridia (kidney-like organs). The body is divided into a head, often with eyes or tentacles, a muscular foot and a visceral mass housing the organs. Covering the body is a thick sheet called the mantle, which in most forms secretes a calcareous shell.
Mollusks have a mantle, which is a shell-like outer cover, and a muscular foot that is used for motion. Many mollusks have their mantle produce a calcium carbonate external shell and their gill extracts oxygen from the water and disposes waste. All species of the phylum Mollusca have a complete digestive tract that starts from the mouth to the anus. Many have a radula, mostly composed of chitin, in the mouth, which allows then to scrape food from the surface by sliding back and forth. Mollusks also have a coelom, made from cell masses, where all organs are suspended. Unlike Coelomates, mollusks lack body segmentation.
Development passes through one or two trocophore stages, one of which (the veliger) is unique to the group. These suggest a close relationship between the mollusks and various other protostomes, notably the Annelids. Mollusk fossils are some of the best known and are found from the Cambrian onwards.
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Taxonmony
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Phylum: Mollusca
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Source: Wikipedia Read more about Molluscs - Misc.
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PICTURES (Click to enlarge)
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| Sculptured top shell |
Smooth turban |
Volva |
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| White hump-back conch |
White rock shell |
Common spider conch |
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| Elegant olive |
Giant Atlantic cockle |
Lynx Cowrie |
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| Rat cone |
Rat volute |
Turrid |
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| Nudibranch |
Tinted Wentletrap |
Sea Lemon Nudibranch |
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| Spanish Shawl Nudibranch |
Blue & White Nudibranch |
Atlantic gray cowrie |
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| Queen Conch |
Cuttlefish |
Spanish Dancer Nudibranch |
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| Hilton's Nudibranch |
Sea Lemon Nudibranch |
Chestnut Cowry |
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| Bleeding tooth |
Florida cone |
Lettered olive |
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| Lined chiton |
Measled cowrie |
Northern siphon whelk |
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| Tiger cowrie |
Banded tulip |
Common dove shell |
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| Tiger cowrie |
Ansodoris Nudibranch |
Octagon murex |
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