THE HEXAPODS AND MYRIAPODA
The insects are most successful animals. Zoologists have described approximately 750 100 species of insects. The actual number of insect species is 30 million. Most of the described species are in tropicalrain forests. The insect species comprise 75% of all living species. There are numerous freshwater and parasitic insect species. But the molt successful insects are terrestrial. The success of these insect is due to their ability to exploit terrestrial habitats.
Evolution of insects: Animals were absent in terrestrial environments of late Silurian and early Devonian periods (about 400 million years ago). The herbaceous plants and the firs forests began to flourish. Enough ozone accumulated in the upper atmosphere. It filters ultraviolet radiation from the sun. Therefore, a large amount of photosynthetic production was available for animal. Animal started living in terrestrial environment. The animals faced little competition from other animals for resources. But they placed may problems in terrestrial life. Support and movement was difficult on land. Similarly regulation of water, ion (electrolyte) and temperature was also a problem on land.
Adaptations in insects: A number of factors are responsible for dominance of insects on terrestrial habitats. These are:
- The exoskeleton adapted the insects on land.
- The evolution of a waxy epicuticle increases the water conserving properties of exoskeleton.
- The evolution of flight also played a big role in success of insects. The ability to fly helps them in many ways. It allows them to use wide resources of food. They can migrate to new habitat.
- They develop desiccation-resistant eggs.
- Their larvae undergo metamorphosis.
- They have high reproductive potential.
- They have different types of mouthparts and feeding habits.