What do most of us know about animals? The answer is very little. There are almost two million species of animals on this planet today and their continued survival after one billion years is testament to their endurance and brilliance. At one extreme they are the big cats and elephants that most of us are familiar with, to the unknown animals somewhere beneath the sea bed.

Animals are usually easy to distinguish from other forms of life because most of them have the ability to move. This rule works very well for most of the animals that live on the land but it is not always the case for those that live in water. Here they live in water and in some cases have trailing arms or tentacles that make them look like plants. A reliable way of identifying animals is by their basic biological features. Their bodies are composed of many cells and they have nerves and muscles that enable them to respond to the world around them. They get the energy that they need by taking in food.

Animals are highly complex and responsive compared to other forms of life. Even the most simplest of animals react quickly to changes around them, shrinking away from potential danger or reaching out for food. The animals that are able to learn from experience and are unique to the animal world, are those animals with well developed nervous systems. The worlds largest living animals, baleen whales can live up to 25 metres long and weigh 120 tons. At the other end of the scale are microscopic organisms and sub microscopic flies and beetles. These animals are so tiny that their weight is negligible but they still possess the body systems that are needed for survival.  Read more...