Slide 1 The first group of organisms we will look at are the sponges in phylum Porifera. They are the representative group of parazoans. The sponges do not have true tissues and do not have symmetry.
Slide 2 The term "Parazoa" literally translates as "beside the animals". This is the first group of animals to evolve and some biologists suggest the sponges should not be classified as animals at all.
Slide 3 The sponges have some characteristics of the animals - they have a motile stage and they are ingestive heterotrophs. However, they do not have true tissues or symmetry - all other animals do. Just like the plants and fungi, the animals evolved from an aquatic protist and the sponges are a completely aquatic group. Most of them live in marine environments but there are some freshwater sponges. Some biologists suggest that the sponges are not truly multicellular but rather a colony of interdependent cells.
Slide 4 One reason that some biologists think they are colonial is because they have such minimal cellular differentiation. There are distinct cell types but they do not function together as tissues and behave in many ways like individual cells living colonially.
Slide 5 The sponges are widespread in marine environments and can be quite beautiful. Many people use natural sea sponges for bathing, painting and other crafts.