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Chapter 15

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Department
Biology
Course
Biology 1225
Professor
Michael Butler
Semester
Fall

Description
Chapter 15 Animal Evolution ***Exam All animals are: 1. multicellular 2. heterotrophic (need to get food outside of own body) 3. aerobes (need oxygen) 4. except for sponges and cynidarians (example: jellyfish, sea anemone) possess three embryonic cell layers – which form tissues, organs, organ systems 5. their cells are unwalled 6. they move (irritability) ***Exam Major trends in evolution include 1. cephalization – (head) 2. symmetry 3. a coelom (fluid filled cavity between intestines and body wall cushions and protects internal organs) 4. segmentation 1. Animals are multicelled heterotrophs that typically ingest food. Their cells are unwalled 2. Animals reproduce sexually and in many cases asexually. They go through a period of embryonic development and most move about during at least part of their life cycle 3. ***Most animals are invertebrates 1 15.2 Animal origins, traits and trends pg. 287 1. The earliest animals were aggregations of cells (multicellular) ***Sponges*** 2. A tissue consists of one or more types of cells that are organized in a specific pattern and that carry out a particular task – In the early lineages embryos had two tissue layers: an outer ectoderm and an inner endoderm. In later lineages, cell movements produced a middle embryonic layer called a mesoderm. The evolution of a three layer embryo allowed an increase in structural complexity 3. Radial symmetry – Cnidarians like jellyfish or sea anemones have radial symmetry (body parts are repeated around a central axis like the spokes on a wheel. Radial animals have no front or back end. They attach to an underwater surface or drift along, so their food can arrive from any direction. 4. Bilateral symmetry – All other animals have bilateral symmetry. They have a right and left half with body parts repeated on either side of the body. Bilateral animals have a distinctive head end that has a concentration of nerve cells 5. Animals with a 3 layer embryo are classified into two groups that differ in the way they develop as embryos . In protostomes – the first opening that forms on an embryo becomes the mouth. Proto means first and stoma means opening. 6. In deuterostomes the second opening becomes the mouth 2 15.3 Invertebrate Diversity pg. 290 Major animal phyla pg. 288 INVERTEBRATES (1 – 8) 1. Sponges (undifferentiated) - Multicellular - asymmetrical body - Aggregation of cells - Digestion is intracellular – Collar cells filter bits of food from water, engulf them by endocytosis then digest them 2. Cnidarians (Jellyfish or sea anemone) - multicellular - radial symmetry - 2 embryonic cells (no mesoderm) - tissues but no organs - uses tentacles with stinging cells to capture food 3. Flatworms (Planarian or tapeworm) - multicellular - bilateral symmetry - 3 embryonic cells - protostome development - a digestive tract with just one opening - ***NO coelom(fluid filled cavity between intestines and body wall) ie. Eucoelom - tissues and organs but no body cavity. - Beginning of a central nervous system – a brain 3 4. Annelids (earthworm) - multicellular - bilateral symmetry - 3 embryonic cells - protostome development - complete digestive system - have a coelom - tissues and organs - a segmented body plan and a true circulatory system with primitive hearts 5. Mollusks (clams, mussels, snails, squid, octopus) - multicellular - bilateral symmetry - 3 embryonic cells - protostome development - a reduced coelom - tissues and organs - have a mantle which generates the hard shell in clams, mussels and snails - the squid and octopus have a more advanced visual acuity - well developed brain which is needed when an animal is predator and needs rapid response to stimulus and rapid movement 6. Roundworms (giant roundworm that lives inside humans sometimes – can also infect pigs and livestock) - multicellular - bilateral symmetry - 3 embryonic cells - protostome development - a true but simple gastrointestinal tract with a mouth and an anus - ***a pseudo coelom or eucoelom - tissues and organs - unsegmented worm with a cuticle that is mottled as the animal grows 4 7. Arthropods (insects, butterflies, spiders(arachnids), crustaceans - multicellular - bilateral symmetry - 3 embryonic cells - protostome development - tissues and organs - an external hard protective exoskeleton(that is periodically molted) that also reduces water loss for life on land and jointed legs - many appendages allowing efficient movement ***First successful land based animal*** 8. Echinoderms (sea star, sea urchins, sea cucumbers) - Multicellular - radial animals with bilateral larvae - These evolved from bilaterally symmetrical ancestors into a radially symmetrical body plan ( example of regressive evolution) - 3 embryonic cells - **deuterostome development - water vascular system and
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