The Animal Kingdom

Which of these is an “animal”?

Answer: They are all animals! Characteristics of Animals: -Heterotrophic -Eukaryotic -Multicellular -Lack cell walls, but have cell membrane 95% = invertebrates (do not have backbone) 5% = vertebrates (have a backbone)

Characteristics Used to Classify Animals Body organization—Does the animal have tissues, or tissues organized into organs, or organ systems? Number of body layers—Does the animal have two or three layers? Body symmetry—Does the animal have radial or bilateral symmetry? Digestive tract or gut—Does the animal’s gut have only one opening or does it have two openings: a mouth for food intake and an anus for expulsion of body waste? Coelom or body cavity—Does the animal have a true body cavity, is it partially formed, or is it absent?

Body Layers There are three different types of germ layers: ectoderm (“ecto” meaning outer and “derm” meaning skin or layer), endoderm (“endo” meaning inner), and mesoderm (“meso” meaning middle)

Body Layers Cells from the ectoderm will form skin and the nervous system. Feathers, scales, hair, and nails also come from the ectoderm. Cells from the endoderm will form the lining of the gut. Most animals have a mesoderm. It gives rise to organs of the circulatory, reproductive, excretory, and muscular systems. The simplest animals, such as the sponges and jellyfish, have no mesoderm.

Body Symmetry Radial symmetry- Animals like hydra, jellyfish, and starfish, are not well suited to rapid locomotion. No one region of the animal always leads. Bilateral symmetry – Animals that have a true head region. Because the head tends to enter a new environment first, nerve cells are usually concentrated in this area.

Body Symmetry

Identify the Symmetry

Digestive Tract Hydra and jellyfish have a saclike gut with a single opening. More complex animals, such as earthworms and birds, have a tubelike gut with a separate mouth and anus.

Digestive Tract or Gut?

Body Cavity / Coelom Coelom - Located between the body wall and the gut, and contains and protects the internal organs The coelom develops from the mesoderm and has lining of cells called the peritoneum The peritoneum also surrounds the internal organs and holds them in place Less complex invertebrates may lack a coelom or may have an intermediate structure called a pseudocoelom

Body Cavity / Coelom

What do you think the advantage of having a coelom is? Allows the animal to grow large Allows space for internal organs such as lungs, heart, stomach, and intestines to expand and contract and to slide by each other as the animal moves The fluid of the cavity may further aid in waste removal and in the circulation of food materials and oxygen