Mollusks are bilaterally symmetrical, and has more than two cell layers, organs, and tissues. The body of mollusks has no cavity. They have a through gut, with a mouth and an anus. They have a pair of kidneys, and reproduce normally.Mollusks have an open circulatory system and have gaseous exchange organs called ctenidial gills. They feed on a wide range of materials, and live in various environments.
Major groups
Mollusca is a very wide range group that includes clams, snails, and octopus. Gastropods (snails) are coiled while bivalves (clams) have two shells that are bilaterally symmetrical.
All Mollusca:
Abalone
Bivalves (ribbed)
Bivalves (smooth)
Bivalves (mussel)
Bivalves (scallop)
Gastropods (high spiral)
Gastropods (low spiral)
Ecological roles
Mollusks which include land snails, freshwater snails, mussels, clams, and slugs, are vital to healthy ecosystems. Land snails, for example, not only provide food for a host of small mammals and birds, but they play vital roles in recycling nutrients in forests. Freshwater snails also provide food for fish, including trout and salmon, and recycle plant and animal waste. Mollusks are also considered ecological indicators, providing a window into the health of and entire ecosystem
Referances
http://www.earthlife.net/inverts/mollusca.html
http://www.msnucleus.org/membership/html/jh/biological/mollusca/lesson1/mollusca1a.html
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