Monday, 28 November 2011

Invertebrate



Animals that lack backbone are called as invertebrates. These invertebrates are seen in all places from deserts to forests and from caves to seabed and even in unbearable Polar Regions. They can also been seen in the air.
And most of the invertebrates are small in their size and only few reach the impressive sizes. For example the heaviest invertebrate is the giant squid and the longest one is the ribbon worms and the smallest one is the rotifers. 
Ribbon Worms


 
Rotifers

Other animals that are considered as invertebrates are spiders, worms, snails, centipedes, clams, jellyfish, crabs and squid.
All the species that belong to invertebrates have their own life cycle. All invertebrates lay eggs and the eggs of some species directly hatch into an adult and some enter into the larvae stage and then move into an adult.


Since the invertebrates are many in number they all share a single characteristic in common.
The first and common characteristic of all the invertebrates is that they all lack backbone
These soft bodied animals maintain their body shape by maintaining their internal pressure. Some invertebrates have hard outer covering called as exoskeleton to protect them from their predators.


The exoskeleton not only prevent the animals from their enemies they also provide a support to their muscles and in the land they prevent the water content from evaporating so that the animal species does not dry up.The body of the invertebrates is of two types. They are radial symmetry and the other one is called as bilateral symmetry.

Bilateral symmetry


 
Radial Symmetry

Invertebrates have simple nervous system. The internal anatomy of the invertebrates differs from each other. Some may have respiratory, excretory and circulatory organs and in some species these organs may be absent. 

With 2 million known animal species on earth nearly 95% of the animals are invertebrates. 
These invertebrates can be found in all the environments from hot desserts to unbearable polar zones. These vertebrates are seen in different shapes, sizes and colours.


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