common types of animals in mollusk group
The Six Classes of Mollusksby Cassandra Pataky
Since 600 million years ago when the first mollusks were formed in the ocean, distinguishable classes emerged among the shells and Phylum Molluska. The following are the six classes of mollusk shells:
1. GASTROPODA
These shells emerged 600 million years ago. No other class has as many species (more than 50,000) or are as widely collected. They extend from the coastline to the abyssal zone and colonize from fresh water to dry land. Gastropods are characterized by their spiral structures and colors.
2. MONOPLACOPHORES
Also emerging at the same time as gastropods, these shells all live on seabeds and only reach about an inch in total length.
3. POLYPLACOPHORES
Emerging 500 million years ago, polyplacophores (aka chitons) live a few inches below the water's surface on reefs. Their shells consist of eight tiny plates layered as shingles with pores. Today there are about 600 species ranging from intertidal areas to the abyssal zone.
4. SCAPHOPODS
About 550 million years ago these shells washed up on beaches around the world. They are small, curved, white tubes formed for specialization purposes. There are 350 species existing today buried in sandy seabeds from the intertidal area to the abyssal zone. There maximum length is five inches and they tend to be white in color.
5. BIVALVES
The first of these shells evolved 425 million years ago during the Cambian or Ordovician period. This class contains approx. 10, 000 species which are mostly marine and freshwater. The largest one is the giant clam and is 4.5 feet long. Bivalves are as their name suggests: two hinged plates (valves) that provide complete protection for the organisms living within them.
6. CEPHALOPODS
Emerging about 525 million years ago, these shells are the most evolved of all six classes and the mollusks are carnivorous. Their shells appear as an "outer hull", but are more commonly internal. There are about 600 of these living species today and, including the giant squid, they may reach lengths of 65 feet.
taken from : http://www.sanibelhistory.org/classes_mollusks.htm
Since 600 million years ago when the first mollusks were formed in the ocean, distinguishable classes emerged among the shells and Phylum Molluska. The following are the six classes of mollusk shells:
1. GASTROPODA
These shells emerged 600 million years ago. No other class has as many species (more than 50,000) or are as widely collected. They extend from the coastline to the abyssal zone and colonize from fresh water to dry land. Gastropods are characterized by their spiral structures and colors.
2. MONOPLACOPHORES
Also emerging at the same time as gastropods, these shells all live on seabeds and only reach about an inch in total length.
3. POLYPLACOPHORES
Emerging 500 million years ago, polyplacophores (aka chitons) live a few inches below the water's surface on reefs. Their shells consist of eight tiny plates layered as shingles with pores. Today there are about 600 species ranging from intertidal areas to the abyssal zone.
4. SCAPHOPODS
About 550 million years ago these shells washed up on beaches around the world. They are small, curved, white tubes formed for specialization purposes. There are 350 species existing today buried in sandy seabeds from the intertidal area to the abyssal zone. There maximum length is five inches and they tend to be white in color.
5. BIVALVES
The first of these shells evolved 425 million years ago during the Cambian or Ordovician period. This class contains approx. 10, 000 species which are mostly marine and freshwater. The largest one is the giant clam and is 4.5 feet long. Bivalves are as their name suggests: two hinged plates (valves) that provide complete protection for the organisms living within them.
6. CEPHALOPODS
Emerging about 525 million years ago, these shells are the most evolved of all six classes and the mollusks are carnivorous. Their shells appear as an "outer hull", but are more commonly internal. There are about 600 of these living species today and, including the giant squid, they may reach lengths of 65 feet.
taken from : http://www.sanibelhistory.org/classes_mollusks.htm
Mollusks are a large group of invertebrate animals. Mollusks have soft bodies, and their bodies are not divided into rings like the segmented worms called annelids . Mollusks don't have legs, though some have flexible tentacles for sensing their environment or grabbing things. Most mollusk species grow a hard shell for protection, but their shell grows in only one or two pieces. It doesn't have joints like the exoskeletons of insects and crustaceans .
There are almost 100,000 species of mollusks around the world, and many tens of thousands more undiscovered. Most mollusk species only live in the ocean, but some live in freshwater or on land. In Michigan there are about 300 species of mollusks known, with more to be found.
There are three main groups of mollusks. Snails ( Gastropoda ) are the most diverse group, there are tens of thousands of species. Nearly all snails grow a spiral shell that is all one piece. A few snail groups have stopped growing shells; they're called slugs . The next largest group is Bivalvia , the clams, oysters, and mussels . These are mollusks with two shells that they can close up tight for protection. Finally there is Cephalopoda , the squids and octopuses. They only live in salt water, so we won't say much about them here. They have no shells, but are larger, smarter, and faster than their relatives in the other groups. Squids and octopuses are all predators; they eat fish, crustaceans, and other mollusks.
taken from : http://www.biokids.umich.edu/critters/Mollusca/
Mollusks were among the first inhabitants of the Earth. Fossils of mollusks have been found in rocks and date back over 500 million years. Mollusk fossils are usually well preserved because of their hard shell.
Most mollusks have a soft, skin-like organ covered with a hard outside shell. Some mollusks live on land, such as the snail and slug. Other mollusks live in water, such as the oyster, mussel, clam, squid and octopus.
Land living mollusks, like the snail, move slowly on a flat sole called a foot.
Ocean living mollusks move or swim by jet propulsion. They propel themselves by ejecting water from their body. For example, the squid ejects water from a cavity within its body, and the scallop ejects water to move by clamping its shell clamp
taken from : http://www.kidport.com/reflib/science/animals/mollusks.htm
Most mollusks have a soft, skin-like organ covered with a hard outside shell. Some mollusks live on land, such as the snail and slug. Other mollusks live in water, such as the oyster, mussel, clam, squid and octopus.
Land living mollusks, like the snail, move slowly on a flat sole called a foot.
Ocean living mollusks move or swim by jet propulsion. They propel themselves by ejecting water from their body. For example, the squid ejects water from a cavity within its body, and the scallop ejects water to move by clamping its shell clamp
taken from : http://www.kidport.com/reflib/science/animals/mollusks.htm