Molluscs 2BIbDF09 10/11

What are molluscs?

Molluscs are invertebrates animals that live in water, and mostly in oceans. There is an estimated number of 100'000 species in the phylum Mollusca. Molluscs appeared in the earliest Cambrian period 545 million years ago. We can define three different groups of molluscs; the Gastropods, the Cephalopods and the Bivalves. All of them have the same body plan separated in three parts. The first part is the foot which is the strong, muscular portion used for locomotion. The second one is the visceral mass, a soft-bodied portion that contains internal organs and the third one is the mantle, that covers and protect the visceral mass. Many molluscs feed by using a rasping organ called a radula. (cf appendix 1)

http://www.andrewgray.com/essays/molluscs.htm

{co { Annexe is FRENCH... You should say APPENDIX Pierre.brawand 16 janvier 2011 à 21:09 (CET)

co

what is a shell? Is it an exoskeleton?

The Gastropods

The Gastropods form the group of molluscs the most important. The Gastropods include the snails whelks, limpets, and the slugs. Why do we call them Gastropods?

The Gastropods meaning stomach-footed. They move by muscle contractions, thanks their ventrally flattened foot.

Where do they live?

Some of them live into the water and the others live in somewhere is humid.

What are the differences between the Land gastropods and the sea gastropods?

The shell of the snails change. the Land snails have thinner shell than the marine snails

The group of gastropods is divided by three under group: The prosobranchs, the nudibrachs and the pulmonés. 

{{co|where did you get this information? In a French website? If this is the case, don't do that. I don't want you to translate. I want you to read in English and to synthesize the main information.}Pierre.brawand 16 janvier 2011 à 21:11 (CET)

The nudibranchs are marine gastropods and they have lost their shell but we called also sea slugs.

These molluscs can be unisexual or hermaphrodite.

They can have a shell like the snails.

The shell is in the shape of spiral,which is used for protection.

They have two pairs of tentacles of which the longest have eyes in the extremity. Although most gastropods are herbivores or detritivores.

The Cephalopods

Cephalopods differ from gastropods and bivalves. Unlike bivalves and most gastropods which have shells, most cephalopods, like the Octopus, miss it. Only a few cephalopods have a heavy external shell (like the Nautilus) or a small and internal shell (like the Squids). They are carnivorous predators made for speed and agility; cephalopods are know for their intelligence and ability to catch their prey. They are found in all oceans of the world. All species of cephalopods have tentacles that they use to catch and hold prey. The tentacles seem to be arms that help them to feed themselves and cling to surfaces, thanks to suction cups on the tentacles too. Cephalopods are great predators thanks to their speed movement, camera eye-vision and their intelligence. They move by jet propulsion. (à dvp) The eyes of the cephalopods don't differ so much with human eyes.

http://sharon-taxonomy2009-p3.wikispaces.com/Mollusca http://www.thecephalopodpage.org/

What are the differences between the species of cephalopods?

http://www.waterencyclopedia.com/Ce-Cr/Cephalopods.html

The Bivalves

Bivalves, including numerous species of clams, oysters, mussels and scallops, have shells divided into two halves hinged together. Most bivalves are sedentary, living in sand or mud in marine and freshwater environments. They use their muscular foot for digging and anchoring.

References

• http://www.earthlife.net/inverts/mollusca.html

Essential Biology with Physiology Campbell/Reece/Simon Second Edition

good start but still a lot of work to do...!Pierre.brawand 16 janvier 2011 à 21:13 (CET)

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