Chapter 32.4, Problem 1CC

Summary Introduction

To describe: The evidence that cnidarians share a more recent common ancestor with other animals than with sponges.

Concept introduction: Sponges belong to a phylum called porifera. They have cellular level of organization that is their body is made up aggregates of cells. They have pores in their whole body. These pores help in exchange of nutrient and also remove waste materials. Sponges are primitive animals that diverged from other animals early in the evolution. Certain recent studies have concluded that the sponges are monophyletic.

Cnidaria is a phylum that contains approximately 10,000 species of animals. The animals in this group are usually aquatic (freshwater and marine). They possess a specialized cell called cnidocyte. The cnidocyte helps in capturing prey. The cnidarians are radially symmetrical and have tissue level of organization.