Mollusks are invertebrate animals that typically have a soft body and secrete a hard shell. They have a head with eyes, mouth and brain. Mollusks can be male, female or hermaphroditic. They reproduce either internally or externally. The three main types of mollusks are bivalves like clams, gastropods like snails, and cephalopods like squid and octopuses. Bivalves have two-part shells and use their muscular foot for burrowing. Gastropods have spiral shells and include sea slugs. Cephalopods are highly intelligent and can change their skin color and texture.

1. MollusksBy Sandra Cash

2. Characteristics of MollusksAll three types of mollusks have the following characteristics:The strong cephalization of the organisms; there is a definite head with a mouth, brain, and eyes. The coelom is reduced to a more definite digestive and intestinal system. There is an excretory system with kidney/nephridium. There is a muscular foot used for locomotion. Some of the mollusks secrete a protective shell that encloses a soft body. Gills are used for respiration. The circulatory system is open with a well-defined heart.

3. MollusksMollusks are either male or female, although it is not easy to tell the difference. Some mollusks are hermaphroditic, meaning they have both male and female reproductive organs. Fertilization can be internal or external; eggs can be laid or larvae can be released into the water column. The larvae are ciliated and known as veligers.

4. MollusksThere are three types of mollusks the pelecypods, gastropods and the cephalopods. First we will look at the pelecypods. Then we will look at the gastropods. Finally we will look at the cephalopds.The pelecypods and gastropods have a mouth and anus that sometimes twist and turn to empty close to each other.

5. PelecypodsThe Pelecypods, which means "hatchet footed," are the kind of mollusks you eat when you eat a clam or a scallop, you are eating the muscular foot. All pelecyods have shells composed of two pieces known as valves. The foot of pelecypods is adapted for burrowing in all species except the sedentary ones, where it is reduced in size. An example of a pelecypod is the cockle. The cockle bends and straightens the foot to jump away from predators in its shallow-water ocean habitat off the island of Espiritu Santo, Vanuatu. Cockles live in sand and mud in shallow water, often in brackish inlets. It burrows until only the siphons project, pulling in water from which the animal strains the minute planktonic organisms on which it feeds.

6. GastropodGastropod means "stomach footed." When you eat conch fritters, you are eating the chopped up and marinated foot of the gastropod snail. Gastropods contain over 35,000 living and 15,000. Typically gastropods have shells that are three-layered, spiral whorl of calcium carbonate, which varies in color, shape, ornamentation, and size according to the species. Within this shell is the tall, coiled body mass. Some forms, such as sea slugs, are shell-less and do not have a tall body mass.There are more than 3,000 known species of sea slugs, and new ones are being identified almost daily. They are found throughout the world's oceans, but are most abundant in shallow, tropical waters. Generally oblong in shape, sea slugs can be thick or flattened, long or short, ornately colored or drab to match their surroundings. They can grow as small as 0.25 inch or as large as 12 inches long. They are carnivores that slowly ply their range grazing on algae, sponges, anemones, corals, barnacles, and even other sea slugs. To identify prey, they have two highly sensitive tentacles, called rhinophores, located on top of their heads. Sea slugs get their coloring from the food they eat, which helps in camouflage, and some even retain the foul-tasting poisons of their prey and secrete them as a defense against predators.

7. CephalopodCephalopod means "head footed." Depending on what meal you are eating, sometimes you are eating the entire squid or octopus, and sometimes just the tentacles! As you can see, mollusks are an important part of the food industry. Cephalopods, the class of mollusks which scientists classify octopuses, squid, cuttlefish and nautiluses. They can change color faster than a chameleon, can change texture and body shape, and, and if those camouflage techniques don't work, they can still "disappear" in a cloud of ink, which they use as a smoke-screen or decoy. Cephalopods are also fascinating because they have three hearts that pump blue blood, they're jet powered, and they're found in all oceans of the world, from the tropics to the poles, the intertidal to the abyss. An example of a cephalopod is the giant squid, which is the largest of all mollusks. The biggest giant squid ever found measured 59 feet in length and weighed nearly a ton. Like other squid species, they have eight arms and two longer feeding tentacles that help them bring food to their beak-like mouths. Their diet likely consists of fish, shrimp, and other squid, and some suggest they might even attack and eat small whales. Scientists don't know enough about these beasts to say for sure what their range is, but giant squid carcasses have been found in all of the world's oceans.

8. Works CitedBrabant, Delphine. National Geographics. 11 March 2011 <http://news.nationalgeographic.com/news/2008/11/photogalleries/missions-santo-species-photos/photo7.html>.Fact Monster. 2007 . 11 March 2011 <http://www.factmonster.com/ce6/sci/A0859723.html>.Fact Monster. 2007. 11 March 2011 <http://www.factmonster.com/ce6/sci/A0812738.html>.Fact Monster. 2007. 11 March 2011 <http://www.factmonster.com/ce6/sci/A0859725.html>.Fact Monster. 2007. 11 March 2011 <http://www.factmonster.com/ce6/sci/A0859722.html>.National Geographic. 2011. 11 March 2011 <http://animals.nationalgeographic.com/animals/invertebrates/nudibranch/>.National Geographic. 2011. 16 March 2011< http://animals.nationalgeographic.com/animals/invertebrates/giant-squid/>Wood, Dr. James B. The Cephalopod Page. 2011. 11 March 2011 <http://www.thecephalopodpage.org/>.

9. Pictures CitedNational Geographics. Web. 11 March 2011. <http://news.nationalgeographic.com/news/2008/11/photogalleries/missions-santo-species-photos/photo7.html>. "New Egg Layer." National Geographics. Web. 11 March 2011. <http://news.nationalgeographic.com/news/2010/09/photogalleries/100923-new-species-sea-slug-nudibranch-science-egg-doily-pictures/>. "Giant Squid." National Geographics. Web. 16 March 2011. <http://animals.nationalgeographic.com/animals/invertebrates/giant-squid/>. "Variation in Shell Morphology in Some Marine Gastropods." University of California Museum of Paleontology. Web. 11 March 2011. <http://www.ucmp.berkeley.edu/taxa/inverts/mollusca/gastropoda.php>"Planktonic Mollusk Larvae." www.photomacrography.net. Web. 11 March 2011. <http://www.photomacrography.net/forum/viewtopic.php?p=63935&sid=29ee29ce336753556becefc6af641c3e>