What Are Animals?
How many species of animals have been identified to date? Viddyoze Review The answer is close to two million and they are the most varied living thing on planet Earth. They have struggled to overcome tremendous obstacles, adapting their lifestyles in order to survive. They range from the animals that we all familiar with, big cats and birds of prey to the animals we have never heard of that live on 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.
Because of their differences in sizes animals can live in different ways. Whales have few natural predators and the same is true of elephants, which is the largest land animal. They are able to process food on a very large scale because of the massive size of their bodies. However they take a long time to reach maturity, which means that they are slow to reproduce. Insects on the other hand are easy prey for many animals and their small size means that their bodies are not as energy efficient as large animals. But because they can breed very quickly when the conditions are in their favour, their numbers can rise at a very fast rate.
Almost all of the world's largest and most familiar animals are vertebrates; these are animals that have backbones. They include the fastest animals on land, sea and air and also the world's most intelligent species (homo sapiens). Vertebrates are all related to each other, sharing a common ancestry that goes back millions of years. However despite the fact that vertebrates lead the animal kingdom in many fields, they only make up a small minority of the animal species known today. Animals without backbones, invertebrates, constitute the vast majority of animal species.
Invertebrates often have very little in common with each other (unlike vertebrates), apart from their lack of a backbone. The giant squid which is the largest invertebrate, can measure over 16 metres long but it is very much an exception. Most of the invertebrates are very small and live in inaccessible habitats.
