All animals that live on land must overcome certain common problems. Terrestrial animals must have:
1. a moist membrane that allows for an adequate gas exchange between the atmosphere and the organism,
2. a means of support and locomotion suitable for land travel,
3. methods to conserve internal water,
4. a means of reproduction and early embryonic development in which large amounts of water are not required, and
5. methods to survive the rapid and extreme climatic changes that characterize many terrestrial habitats.
