Question

Outline the major events in animal evolution/themes of animal evolution. including types of body cavities and their descriptions, and give examples of animals that display these themes

Answer 1

Evolution in animal.

Evolution in animal takes place from single cell Protozoa to multicellular human being. Human being has topmost position on evolutionary tree.

During evolution, single cell Protozoa evolve into multicellular metazoa. Metazoa includes large number of animal according to the sequence of evolution. The first member of metazoa is sponges future also known as Porifera. Porifera has cellular level of Organisation in which there is no any tissue system. After that nematodes are involved in evolutionary history. Who have tissue grade of organisation and first nervous system appear in this animal. In respect of digestive system Protozoa have intracellular digestive system with no body cavity. Porifera also have intracellular digestion and a body cavity with single opening. Coelentrates and Platyhelminthes are also have alimentary Canal with single opening and body cavity is tube like. All the animals are called acoelomate. After Platyhelminthes animals have pseudocoelom or true coelome. During evolution the elementary canal and body cavity becomes more complex. Body cavity of higher animals are tube within a tube like. In which alum this type of arrangement develop entary Canal completely separate from the body cavity. This type of arrangement develop more efficient digestion of food. Likewise every organ system becomes more and more Complex in higher animal according to the events of evolution.