Thursday, March 22, 2012

MOLLUSCA, THE SHELLED INVERTEBRATES OF ANIMAL WORLD

 Introduction :Animal world consist of a particular group of animals which have their body covering made of of shell which is made up of calcium carbonate. Having been composed of calcium carbonate the shell is very hard in texture and give protection to the whole internal vital organs of the body.Inside the shell the various organs of the body are found in compact form concentrated in a mass  and this mass of all the internal visceral organs is known as "visceral mass". The body of these animals consists of the following parts which are anterior head, ventral muscular foot and visceral mass.

Why are they called the macroinvertebrates?: As the molloscs are the invertebrates with comparatively large sized body in comparison to all the other invertevrates from protozoa to arthropoda, they are called macro - invertebrates. Invertebrate animals with large sized body are a little bit different from micro invertebrates in the sense that they have more devveloped systems and structures in the body. Their digestive system, respiratory system,circulatory system,excretory system an reproductive systems  and  nervous systems are all well-developed  than the microinvertebrates.So they are considered to be one step forward in the developmental step according to the Naturalists.

Economic importance of macroinvertebrates including the animals of phylum mollusca: Molluscs and the other macro invertebrates are economically very important animals of nature. They use to live in aquatic and semiaquatic habitat. They always live in association with other animals and plants of nature along with the nonliving components like water, soil temperature, light and dissolved nutrients.
Molluscs help to filter the impure water and purify it. Molluscs use to eat the various dissolved and decayed vegetable materials of the inhabiting water turning the water clear and transparent. So, they are said to be helpful in water purification in the various types of inland waters like rivers, lakes, ponds, streams and pools.

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