Topic 7: Animal Diversity Ch. 32-34 Characteristics of Animals pp.704-705 Animals: Are eukaryotic Are multicellular Are ingestive heterotrophs Have no cell walls Most are motile Most have tissues organized into organs organized into systems. Characteristics of Animals Animal taxa are organized based on these distinguishing characteristics: Symmetry Tissue layers Body cavity Skeletal system Symmetry pp.708-709 Symmetry - The arrangement of parts in relation to planes and centralized axes. Asymmetrical - No plane will consistently divide an organism into equal parts. Symmetrical - One or more planes will divide an organism into equal parts. Fig. 33.40 Symmetry Radial symmetry More than one plane can divide the animal into equal parts. E.g. Jellyfish There is an oral (mouth) and aboral (anus) end. There is no head. This symmetry is best suited to sessile animals or those that move in any direction. Symmetry Bilateral Symmetry Only one plane can divide the animal into equal parts. E.g. Humans Bilaterally symmetrical animals can be divided into anterior (front) and posterior (back), as well as dorsal (top) and ventral (bottom) parts. Fig. 32.7 Fig. 32.7 1
Symmetry Bilateral animals move in one direction and are cephalized. Cephalization Concentration of sensory structures at the anterior of the animal. This results in the formation of a head. If one end of the organism always encounters a new environment first, it makes sense to have most sensory organs there. To process this information, a complex nervous system is needed. Therefore, bilateral animals usually have a more complex and centralized nervous system than radially symmetrical animals. Tissue Layers p. 709 Fig. 49.2 During embryonic development, animals have up to three tissue layers (germ layers). As the organism matures these tissues become other parts of the body: 1. Ectoderm Covers the early embryo. It becomes the skin and nervous system. 2. Mesoderm Makes up the middle of the embryo. It becomes bone and muscle. 3. Endoderm Inner layer of the embryo. It becomes the digestive system. Tissue Layers Some animals have no tissue layers. Others have two and are called diploblastic. Those with three are called triploblastic. 2
pp.709-710 If an animal has three tissue layers, it can be placed into one of three groups based on its body cavity. Body cavity (or coelom) A fluid filled space inside of an animal. It is not the same as the space inside of the digestive system (the gut or lumen). A coelom allows for greater surface area and greater complexity. Acoelomate No body cavity. Fig. 32.8 Pseudocoelomate There is a fluid filled space with mesodermally derived tissue on only one side. Fig. 32.8 Eucoelomate There is a fluid filled space lined by mesodermally derived tissue on all sides. Fig. 32.8 In some animals the coelom serves as a skeleton or it can help with circulation. Hemocoel - Coelom used for circulation. Hemolymph is moved around the cavity to transport nutrients, waste and gases. Since blood vessels are not used, this type of circulation is called an open circulatory system. Fig. 33.20 Skeletal System pp.1187-1190 The functions of skeletal systems are support, movement, and protection. There are three basic types: 1. Hydrostatic skeleton Fluid held under pressure in a body compartment. Muscles can work against this pressure to move the organism. E.g. earthworm Fig. 50.35 3
Skeletal System 2. Endoskeleton A hard internal skeleton inside of soft tissue. E.g. Humans. Skeletal System 3. Exoskeleton A hard skeleton that encases the outside of the animal. E.g. beetles Fig. 50.36 Fig. 50.34 Challenge - Rank the types of skeletons from most protection to least protection: - Why don t all organisms have the most protective skeleton? Animal Phyla - We will examine the characteristics that distinguish animals in seven different phyla. - Porifera - Cnidaria - Platyhelminthes - Nematoda - Annelida - Arthropoda - Chordata Phylum Porifera pp.717-721 ~ 9000 species. E.g. Sponge Sponges are asymmetrical. There is only a cellular level of organization, therefore no tissues and no coelom. Fig. 33.4 Phylum Porifera They have an endoskeleton made of flexible spongin and rigid glass spicules. Sponges are the least complex animals. They are all aquatic and sessile. There is no nervous system. Fig. 33.4 4
Phylum Cnidaria pp.721-724 ~ 10,000 species. E.g. Hydra Cnidarians are radially symmetrical. They are diploblastic (only endoderm and ectoderm). There is no coelom. They have a hydrostatic skeleton made from water in their gastrovascuar cavity. Coral produce an exoskeleton. Phylum Cnidaria They are all aquatic. Some are sessile, some motile, and some alternate between sessile and motile forms. There is a diffuse nerve net and sensory cells located around the periphery of the animal. Fig. 33.5 Phylum Platyhelminthes pp.724-727 ~ 20,000 species. E.g. Planaria Platyhelminthes are bilaterally symmetrical. They are triploblastic and acoelomate. They have a hydrostatic skeleton. Fig. 33.10 Phylum Platyhelminthes They all live in wet habitats. There is cephalization in some species with nerve ganglia concentrated and sense organs concentrated in the head. Fig. 33.12 Phylum Nematoda pp.734-735 ~ 25,000 species. E.g. Ascaris Nematodes are bilaterally symmetrical. They are triploblastic and pseudocoelomate. Their pseudocoelom provides a hydrostatic skeleton. Fig. 33.26 Phylum Nematoda Ascaris is a parasite but most are free living herbivores. There is limited cephalization with a nerve ring around the mouth and sense organs concentrated in the head. 5
Phylum Annelida pp.732-734 ~ 16,000 species. E.g. Earthworm Annelids are bilaterally symmetrical. They are triploblastic and eucoelomate. They are segmented Segmented Animal s body is divided into a series of repeated sections. Phylum Annelida The segments are fluid filled and act as a hydrostatic skeleton. All live in wet habitats. There is cephalization with nerve ganglia and sense organs concentrated in the head. Fig. 50.35 Fig. 33.24 Phylum Arthropoda pp.735-743 ~ 1,500,000 species. E.g. Grasshopper Arthropods are bilaterally symmetrical. They are triploblastic and eucoelomate. They are segmented with a jointed exoskeleton. Fig. 33.35 Phylum Arthropoda Arthropods can be found in most habitats on Earth. There is cephalization with a brain and sense organs concentrated in the head. Fig. 33.39 Phylum Chordata pp.745, Ch.34 ~ 60,000 species. E.g. Boney fish and mammals (both in the subphylum Vertebrata) Chordates are bilaterally symmetrical. They are triploblastic and eucoelomate. There is an endoskeleton. Fig. 34.19 Fig. 34.39 Phylum Chordata Chordates can be found in most habitats on Earth. There is advanced cephalization with a brain and sense organs concentrated in the head. We will focus on subphylum Vertebrata, which includes all animals with a backbone. 6