Mollusks

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 * Mollusks are soft-bodied animals that usually have an internal or external shell
 * Mollusks include octopi, snails, slugs, clams and squids.
 * All underwater mollusks are common in the fact that they have a trochophore stage in which it can freely move about.
 * Even though mollusks come in a vast majority of shapes and sizes, the all have a basic body composition.
 * This is split into four parts the foot, mantle, shell and visceral mass.
 * The foot allows the mollusks to move and can be tentacles or a flat structure.
 * The mantle is the thin layer of tissue that covers its body
 * The shell which is made by glands in the tissue protect the mollusks organs.
 * The visceral mass is all of its internal organs
 * Mollusks can be either carnivores, filter feeders, parasites or herbivores.
 * Snail and slugs use a Radula to eat and grab food. Herbivores use their radula to scrap out algae of rocks or tissue of plants.
 * Octopi and sea slugs use jaws to eat their prey. Octopi use both poisons and tentacles to gain their prey.
 * Others like clams use gills to filter feed.
 * Most sea mollusks use gills located inside their mantle cavity to absorb oxygen.
 * Land snails breath directly from the mantle cavity, thus it needs to be constantly wet.
 * Mollusks either have an open or closed circulatory system
 * in an open the blood flows around the body to the sinuses, to the gills then back to the heart.
 * A closed circulatory system is mush faster and is meant for faster mollusks
 * Mollusks excrete ammonia using nephridia.
 * Simple lazy animals like the snail have a simple nervous system whereas a octopi has a complex system connected to the brain.
 * Mollusks use their foot to move, octopi combines their tentacles with jet propulsion to get its rapid movement
 * Mollusks tend to reproduce an enormous amount of eggs.
 * Gastropods are shell-less or single shelled mollusks that move by using a muscular foot located on the ventral side.
 * These include sea butterflies, snails, slugs, sea hares and nudibranches.
 * When one shelled gastropods are attacked they retreat back into their shell and block the opening with their foot.
 * Non shelled defend themselves with toxins and chemicals that repels predators
 * Bivalves have two shells that are held together by a muscle.
 * These typical include clams, oysters, mussels, and scallops.
 * Bivalves do not move much and grow in huge colonies attached to one area.
 * They filter feed through their gills and also use long muscular extensions to collect food from sediments
 * Cephalopods are soft-bodied mollusks in which the head is attached to a single foot.
 * Their foot is either tentacles or arms.
 * These include octopi, nautiluses, cuttlefishes and squids.
 * They also contain eyes that allow them to see and sense objects around them.
 * They contain the most complex nervous system out of all the mollusks. [[image:http://www.butterflyrevolt.com/images/2009/04/octopus.jpg width="399" height="296"]][[image:http://www.entropyalwayswins.com/wp-content/uploads/2010/01/t761279a.gif width="388" height="285"]][[image:http://www.aquariumofpacific.org/images/olc/nautilusj.baecker_berlin_zoo_aquarium_pd600.jpg width="395" height="299"]][[image:http://4.bp.blogspot.com/_9rgM0VivwjY/TOo2q99QYxI/AAAAAAAAAWg/fJ79fmbe2zg/s320/bivalve.jpg width="398" height="295"]]