1. Mollusca

2. classes

3. Mollusca is one of the most diverse groups of animals on the planet,
at least 50,000 living species (and more likely around 200,000).
It includes such familiar organisms as snails, octopuses, squid, clams, scallops, oysters, and chitons.

4. Mollusca also includes some lesser known groups like the monoplacophorans, a group once thought to be extinct for millions of years until one was found in 1952 in the deep ocean off the coast of Costa Rica.

5. Molluscs are a group of organisms that all have soft bodies which typically have a "head" and a "foot" region.
Often their bodies are covered by a hard exoskeleton, as in the shells of snails and clams or the plates of chitons.

8. part of almost every ecosystem in the world
molluscs are extremely important members of many ecological communities.
They range in distribution from terrestrial mountain tops to the hot vents and cold seeps of the deep sea, and range in size from 20-meter-long giant squid to microscopic aplacophorans, a millimeter or less in length, that live between sand grains.

9. all molluscs share some unique characteristics that define their body plan.
The body has a head, a foot and a visceral mass.
This is all covered with a mantle (also known as a pallium) that typically secretes the shell.
In some groups, like slugs and octopuses, the mantle is secondarily lost, while in others, it is used for other activities, such as respiration.

10. The buccal cavity, at the anterior of the mollusc, contains a radula (lost in bivalves) — a ribbon of teeth supported by an odontophore, a muscular structure. The radula is generally used for feeding. The ventral foot is used in locomotion. This foot propels the mollusc by utilizing muscular waves and/or cilia in combination with mucus.