Types of alimentary canal are:
In this, mouth and anus or clocal aperture are present. E.g. from Nematodes to Chordates
In this, only one opening i.e. mouth is present. E.g. flatworms
Organisms having two germs layers in the body – outer ectoderm and inner endoderm. E.g. Sponges and Coelentrates
Organisms having three germ layer-ectoderm, mesoderm and endoderm. E.g. flatworms to chordates
- Gills in aquatic animals, tadpoles of amphibians, some mollucs and some echinoderms.
- Tracheae in terrestrial arthropods.
- Book lungs in arthropods.
- Lungs in terrestrial animals.
- Open circulatory system: Blood flows through large open spaces.
2.Cloud circulatory system: Blood flows in definite vessels in definite circuit and blood is in direct contact with the cells. E.g. annelids, vertebrates