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Molluscs

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The word mollusk comes from a Latin word meaning “soft”, which refers to the soft mantle that covers the mollusks, which then secretes the enzymes to form the calcium carbonate shell that protects their boy. The phylum Mollusca are invertebrates containing some sort of a calcium-carbonate shell to cover their soft mantle which secretes the enzymes that make up this shell. Mollusca is one of the most diverse phyla in the world, only second to insects.
The earliest mollusk species that date back all the way to the Cambrian time period (about 542 million years ago) include chitons and conchifers. Most of the fossils that have been found are extremely small, only about 1-5 mm. The oldest known cephalopods, which include squids, octopi, and cuttlefish, date back to much later times, in the Late Cambrian era, which ended around 488 million years ago. The fossil record gives very little evidence to prove how mollusks came about and evolved into what they are today. Because of the little evolutionary evidence, scientists have turned to comparative molecular biology. Biologists have inferred from studies that Phylum Mollusca and Phylum Annelida, which consists of segmented worms, share a common ancestor. The strongest evidence that they share a common ancestor is found in their embryonic stages. They both have pear-shaped larva called trochophore in the first stage of development. In both phyla, these larva have cilia that project from either end of the trochophore and encircle the middle. These cilia function by propelling trochophore through the water and drawing food into their mouths. Trochopheres that are free-swimming also aid in the dispersal of other marine mollusks. However, terrene mollusks and many marine-living annelids devel...

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...ability of a mollusk’s muscular foot to grasp things, such as food, has been adapted into what are now the tentacles of an octopus or squid. The calcium-carbonate shell found in most mollusks is a variety of sizes, shapes, and colors, but most of them have a single function: to protect the mollusk’s soft mantle and to prevent predators from eating them.

Works Cited

Campbell, Dana, and Jennifer Hammock. "Mollusca — Details." Encyclopedia of Life. Encyclopedia of Life, n.d. Web. 13 Mar. 2014.

Foster, Bethney. "Mollusk Life Cycle." EHow. Demand Media, 26 Aug. 2009. Web. 25 Mar. 2014.

Salvini-Plawen, Luitfried Von. "Mollusk (animal Phylum)." Encyclopedia Britannica Online. Encyclopedia Britannica, n.d. Web. 25 Mar. 2014.

"Phylum Mollusca." Phylum Mollusca. N.p., n.d. Web. 25 Mar. 2014.

"Mollusk." - New World Encyclopedia. N.p., 30 Apr. 2006. Web. 29 Mar. 2014.
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