Porifera | Animalia | Diversity in Living Organisms

layers of cells: one makes up cells on the outside of the body, and the other makess the inner lining of the body. Some of these species live in colonies (corals), while others have a solitary like-span (Hydra). Jellyfish and sea anemones are common examples (see Fig. 7.13). 7.5 Animalia These are organisms which are eukaryotic, multicellular and heterotrophic. Their cells do not have cell-walls. Most animals are mobile. They are further classified based on the extent and type of the body design differentiation found. Tentacles Tentacles Stinging cell 7.5.1 PORIFERA The word means organisms with holes. These are non-motile animals attached to some solid Mouth support. There are holes or 'pores', all over the body. These lead to a canal system that helps in circulating water throughout the body to bring in food and oxygen. These animals are covered with a hard outside layer or skeleton. The body design involves very Epidermis Mesoglea- Gastrodermis Gastrovascular cavity minimal differentiation and division into Sea anemone tissues. They are commonly called sponges, and are mainly found in marine habitats. Some examples are shown in Fig. 7.12. Foot Hydra Fig. 7.13: Coelenterata 7.5.3 PLATYHELMINTHES The body of animals in this group is far more complexly designed than in the two other groups we have considered so far. The body is bilaterally symmetrical, meaning that the left and the right halves of the body have the same design. There are three layers of cells from which differentiated tissues can be Еuplectelia Sycon made, which is why such animals are called triploblastic. This allows outside and inside body linings as well as some organs to be made. There is thus some degree of tissue formation. However, there is no true internal body cavity or coelom, in which well- developed organs can be accommodated. The body is flattened dorsiventrally, meaning from top to bottom, which is why these animals are called flatworms. They are either free- living or parasitic. Some examples are free- living animals like planarians, or parasitic animals like liverflukes (see Fig. 7.14 for examples). Spongilla Fig. 7.12: Porifera 7.5.2 COELENTERATA These are animals living in water. They show more body design differentiation. There is a cavity in the body. The body is made of two