Sources

http://www.sheppardsoftware.com/animalpages/animal-family-6.htm

http://www.oceaninn.com/guides/mollusks.htm

http://www.greenfacts.org/glossary/mno/mollusk.htm

http://www.bishopmuseum.org/research/natsci/waipiostudy/students/meet_the_critters/mollusks/introduced/Pomacea_canaliculata.htm

http://hometown.aol.com/ksmith9526/MolluskInformation.htm

www.mcwdn.org/Animals/Mollusks.html

www.sci.sdsu.edu/classes/bio201/mol.annel.htmlhttp://www.sheppardsoftware.com/animalpages/animal-family-6.htm

Anatomic Features of the Average Mollusk

Mucous gland: mucus-secreting organ
Digestive gland: organ that performs the functions of a liver and pancreas.
Crop: grinds up food before it is sent to gizzard to be further ground up.
Stomach: digestive cavity.
Shell: hard protective covering
Copulatory bursa: cavity related to the genital organs.
Heart: blood-pumping organ.
Pericardium: cavity related to the kidneys, situated around the heart.
Nephridium: organ that performs the functions of kidneys.
Genital opening: opening to the genital organs.
Excretory pore: opening through which a mollusk excretes its bodily wastes.
Gill: respiratory organ.
Pleural gland: tear-secreting organ
Pedal gland: organ related to the foot.
Mouth cavity: entrance to the digestive tract.
Tentacle: organ of touch
Eye: sight organ.
Cerebral ganglion: brain

What is a Mollusk

Mollusks are the large and diverse phylum Mollusca, which includes a variety of familiar animalsknown for their decorative shells or as seafood. These include tiny snails, clams, and abalone to larger organisms such as squid, cuttlefish and the octopus There are some 112,000 species within this phylum.

Interesting Facts

Cephalopods such as squid have eyes with lenses, retinas, and other features just like vertebrates. Some gastropods have a well-developed sense of smell and can find food in the water at a large distance. Predators can also be detected and so the mollusk can avoid them. Some mollusks exhibit complicated mating behavior. Some cephalopods possess an amazing ability to learn from experience.
The mollusk phylum is the second largest phylum in the animal kingdom, after the arthropods. Estimates of the number of mollusk species have sometimes exceeded 100,000.

Comparisons With Other Phylums

There are many simmilarities between the annelids and the mollusks. biologists believe that the two phyla are very closely related, branching off from a common ancestor during the precambrian period, about 600 million years ago. The mollusks are bilateral like the annelids. They also share a one-way digestive system characteristic. molluscs are the only phylum of ceolomate without segment bodies. they both have a hydrostatic skeleton for movement. Trochophores the larval stage of life for a mollusk, also appears in segmented worms, in the phylum annelida. .The octopus and the squid, 2 species of mollusk, have some of the most complex nervous systems, held by invertebrates. the giant squid is the world's largest invertebrate.

Habitat and Adaptations

One of the most widespread and successful forms of life, mollusca has managed to make a living in all but a few places. Mollusks can be found in every part of the oceans, from the deep trenches to the shallows, the arctic to the equator. They also adapted to live on land, though not as extensively and in water. Snails, as well as a smaller number of other mollusks, can be found in large numbers in the rainforest canopies, but can also be seen in your backyard. One land type which mollusks have not been able to invade yet are the deserts. Their skin is very moist and requires the presence of water, or else it dessicates. To stop this unpleasant death, land dwelling snail have a thick layer of skin at the opening of their shell which keeps moisture inside. The snails also produce a coat of slime or mucus which stops it from being dried out.

Reproduction

Mollusk reproduction is most commonly done externally, with the release of eggs and sperm into the environment resulting in the fertilization of the eggs. The larvae formed from this type of reproduction are usually free swimming, and either settle of the ocean floor or drift to mature. Some members of the phylum, such as tentacled mollusks and some types of snails, fertilize their eggs internally. Some mollusks are hermaphrodites. They can alternate between the production of male and female gametes, which gives the animal another potential mate... itself.

Mollusks produce a special kind of larvae known as a trochophore, which is translucent and free-swimming. They are round or pear-shaped, and are surrounded by a ring of cilia called the prototroch which propels the larvae through its environment. Also found on the trochophore, above the prototroch, is an ocellus (a simple eye) and a tuft of cilia. Below the belt of cilia are the mouth, stomach, anus, and solenocyte, which regulates internal salt-water balance. In some mollusks, marine snails and bivalves, the trochophore enters a second stage called the veliger before the animal if fully matured. In this stage, the larvae begins to develeop a foot and shell. Trochophores also appear in segmented worms, in the phylum annelida. This fact has led biologists to believe that the two phyla are related, and probably branched off from a common ancestor during the precambrian period, about 600 million years ago.