Chapter 33 - Invertebrates. This chapter presents the following content: This chapter describe how a sponge feeds and digests its food, list the characteristics of the phylum Cnidaria that distinguish it from other animal phyla, list the four classes of Cnidaria and distinguish among them based on life cycle morphology, list the characteristics of Platyhelminthes and distinguish among the four classes, describe the features of molluscs and distinguish among the four classes. | CHAPTER 33 INVERTEBRATES Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Section A: Parazoa 1. Phylum Porifera: Sponges are sessile with porous bodies and choanocytes More than a million extant species of animals are known, and at least as many more will probably be identified by future biologists. Animals are grouped into about 35 phyla. Animals inhabit nearly all environment on Earth, but most phyla consist mainly of aquatic species. Most live in the seas, where the first animals probably arose. Terrestrial habitats pose special problems for animals. Only the vertebrates and arthropods have great diversity. Introduction Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Our sense of animal diversity is biased in favor of vertebrates, the animals with backbones, which are well represented in terrestrial environments. But vertebrates are just one subphylum within the phylum Chordata, less than 5% of all animal species. Most of the animals inhabiting a tidepool, a coral reef, or the rocks on a stream bottom are invertebrates, the animals without backbones. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Based on both molecular evidence and the morphology of their choanocytes, sponges represent the lineage closest to the colonial choanoflagellates. The germ layers of sponges are loose federations of cells, which are not really tissues because the cells are relatively unspecialized. Sponges are sessile animals that lack nerves or muscles. However, individual cells can sense and react to changes in the environment. 1. Phylum Porifera: Sponges are sessile with porous bodies and choanocytes Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings The 9,000 or so species of sponges range in height from about 1 cm to 2 m and most are marine. About 100 species live in fresh water. The body of a simple sponge resembles a sac perforated with holes. Water is drawn through the pores . | CHAPTER 33 INVERTEBRATES Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Section A: Parazoa 1. Phylum Porifera: Sponges are sessile with porous bodies and choanocytes More than a million extant species of animals are known, and at least as many more will probably be identified by future biologists. Animals are grouped into about 35 phyla. Animals inhabit nearly all environment on Earth, but most phyla consist mainly of aquatic species. Most live in the seas, where the first animals probably arose. Terrestrial habitats pose special problems for animals. Only the vertebrates and arthropods have great diversity. Introduction Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Our sense of animal diversity is biased in favor of vertebrates, the animals with backbones, which are well represented in terrestrial environments. But vertebrates are just one subphylum within the phylum Chordata, less than 5% of all animal species. Most of the .
