Chapter 17 Part I - BIOS 1063 Chapter 17 Evolution of...

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BIOS 1063 Chapter 17 Evolution of Animals I. Overview of Animal Diversity A. Characteristics of Animals 1. Multicellular 2. Heterotrophs Ingestion of food 3. Most animals reproduce sexually (animals prefer sex, now that’s a surprise). 4. During development animals form the following stages: 1) zygote, fertilization 2) blastula , which is a hollow ball of cells (in humans, the blastula is the stage that implants in the uterus). 3) Gastrula: this where 3 germ layers form 3 germ layers: 1. Endoderm -forms the digestive tract, 2. Ectoderm forms the skin and nervous system , 3. Mesoderm -forms muscle, bones, blood. Some animals have a life history where they change from a sexually immature juvenile form called Larva. Larva are morphologically distinct from the adult, they even eat different foods- may even have different habitats. Metamorphosis- change from the larva stage to the sexually mature adult stage. Larva when it has fed enough and reaches a certain size, it will form a cocoon -the pupa stage where all the internal organs break down and reform into an adult organism. Dormant genes are expressed to form the adult. B. Cambrian Explosion: Animals evolved from a colonial flagellated protist (protozoan) that lived in the Precambrian seas. By the late Precambrian-a diversity of animals had evolved, then came the Cambrian explosion. Cambrian period : 545 million years ago, animal diversity exploded. In a span of 10 million years: all the major animal body plans we see today evolved. This is so distinctly marked in the fossil records that it was given its own period in geologic history i.e. the Cambrian Period. C. Animal Phylogeny: 4 major branch points in animal evolution 1. Multicellularity 2. True Tissues 3. Body plans Radial symmetry vs Bilateral symmetry 4. Body Cavities-Pseudocoelom and -true coelom We are most comfortable with vertebrate animals (animals that have backbones) such as horses, dogs, cats, elephants, frogs, birds fish etc. Vertebrates only make up about 5% of all animals. Invertebrates make up the other 95% of the animals on this planet.
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II. Major Invertebrate Phyla A: Sponges -Phylum Porifera named for their pores. These animals are sessile ( they don't move) and benthic ( live at the bottom of ocean or lakes). Sponges are the most primitive of animals on our planet, They have no true tissues-just groups of cells, not really connected into a tissue. 1- Poracytes -outside layer of cells that form the pores. 2- Flagellated Choanocytes line the interior of the organism around the central cavity. Flagella beat in synchrony and bring water into the cavity from outside pores. Water brings in the nutrients (bacteria and protists) for the sessile sponge to eat. Amoebacytes are cells that move around and distribute the nutrients throughout the sponge. B.
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This note was uploaded on 06/02/2011 for the course BIO 1083 taught by Professor Williamson during the Spring '08 term at University of New Orleans.

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Chapter 17 Part I - BIOS 1063 Chapter 17 Evolution of...

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