General features of animals

The following features characterize members of the Kingdom Animalia:

(d) Active Movement.
The ability of animals to move more rapidly and in more complex ways than members of other kingdoms is perhaps their most striking characteristic, one that is directly related to the flexibility of their cells and the evolution of nerve and muscle tissues. A remarkable form of movement unique to animals is flying, an ability that is well developed among vertebrates and insects such as this butterfly. The only terrestrial vertebrate group never to have evolved flight is the amphibians.