Chapter 31.1, Problem 2C

Summary Introduction

To explain: The ways in which cnidarians differ from sponges.

Concept introduction: All sponges belong to a phylum called Porifera. They are the simplest animals with cellular level of organization. They have diverged from other animals early in the evolution. The phylum Cnidaria comprises approximately 9000 species. It includes hydra, jellyfish, sea anemones, corals, and others. Most of them are predominately marine, and others are freshwater species. The body is composed of only two layers of cells. The body exhibits radial symmetry.