Monday, June 20, 2011

Mollusks



{ Characteristics }

Mollusks are soft-bodied animals that usually have an internal or external shell. All mollusks have a mantle.


Reproduction

Mollusks have one mean of reproducing. They reproduce sexually.

Mollusks can reproduce sexually through internal or external fertilization. Many gastropods and bivalves reproduce using external fertilization. They release enormous numbers of eggs and sperm into open water that fertilize and develop into free-swimming larvae. Cephalopods and certain gastropods reproduce using internal fertilization. Some mollusks are hermaphroditic, but usually fertilize eggs from another.


Examples of Mollusks

There are three major classes of mollusks: Gastropoda, Bivalvia, and Cephalopoda. The class Gastropoda includes pond snails, land slugs, sea butterflies, sea hares, limpets, and nudibranchs. They are shell-less or single-shelled mollusks that move by using a muscular foot located on the ventral side. The class Bivalvia include clams, oysters, mussels, and scallops. They have two shells that are held together by one or two powerful muscles. The class Cephalopoda includes octopi, squids, cuttlefishes, and nautiluses. They are typically soft-bodies mollusks in which the dead is attached to a single foot. The foot is divided into tentacles or arms.


Vocabulary

trochophore - free-swimming larva stage of an aquatic mollusk

foot - muscular part of a mollusk

mantle - thin layer of tissue that covers most of a mollusks body

shell - structure in mollusks made by glands in the mantle that secrete calcium carbonate

visceral mass - area beneath the mantle of a mollusk that contains the internal organs

radula - tongue-shaped structure used for feeding by snails and slugs

siphon - tubelike structure through which water enters and leaves a mollusk’s body

open circulatory system - system in which blood is not always contained within a network of blood vessels


Works Cited

http://science.plazza.us/wp-content/uploads/2011/05/mollusks.jpg

http://kentsimmons.uwinnipeg.ca/16cm05/1116/33-19-GastropodsCollage.jpg

http://cas.bellarmine.edu/tietjen/AnimalDiversity/bivalvia01.gif

http://cas.bellarmine.edu/tietjen/images/ng_nautilus_1.jpg

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