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Unformatted text preview: Chapter 25 Chapter 25
Animal Evolution – The Invertebrates Characteristics of Animals Multicelled heterotrophic eukaryotes Reproduce sexually, and perhaps Require oxygen for aerobic respiration asexually Motile at some stage Develop from embryos Symmetry RADIAL BILATERAL
Fig. 25-5, p.406 Animal Tissues Animal Tissues Ectoderm Endoderm Mesoderm The Gut The Gut Region where food is digested and then absorbed Saclike gut Complete digestive system – One opening for taking in food and expelling waste – Opening at both ends; mouth and anus (acoelomate, pseudocoelomate, coelomate) BODY CAVITIES BODY CAVITIES Two Coelomate Lineages Two Coelomate Lineages
Protostomes Mollusks Annelids Arthropods Deuterostomes Echinoderms Chordates The lineages differ from each other in three ways: TYPE OF EARLY CLEAVAGE AFTER FERTILIZATION METHOD OF COELOM FORMATION FATE OF THE FIRST PORE Segmentation Segmentation Repeating series of body units Units may or may not be similar to one another Earthworms segments appear similar Insects segments may be fused and/or have specialized functions Major Animal . Phyla Major Animal . Phyla Echinoderms . Chordates Arthropods Annelids Coelomate Ancestry Mollusks Rotifers Roundworms Bilateral Ancestry Radial Ancestry Multicelled Ancestry Flatworms Cnidarians Sponges Single-celled, protistanlike ancestors Animal Origins Animal Origins Originated during the Precambrian (1.2 billion 670 million years ago) From what? Two hypotheses:
– Multinucleated ciliate became compartmentalized – Cells in a colonial flagellate became specialized Phylum Placozoa Phylum Placozoa One living species, Tricoplax adherens Simplest known animal Twolayer body, 3 mm across Fig. 25-11, p.409 Sponges Phylum Porifera Sponges Phylum Porifera No symmetry No tissues No organs Flagella in collar cells circulate water, amoeboid cells digest/ transport food (filter feeder) Reproduce sexually Microscopic swimming larval stage Phylum Cnidaria Phylum Cnidaria Only animals that produce nematocysts Nerve net Hydrostatic skeleton Saclike gut Diploblastic capsule’s lid at free surface of epidermal cell trigger barbed thread inside capsule nematocyst
Fig. 25-13, p.410 Flatworms: Flatworms: Phylum Platyhelminthes Acoelomate, bilateral, cephalized, triploblastic animals systems All have simple or complex organ Most are hermaphrodites Planarian Organ Systems Fig. 25-16, p.412 Roundworms (Nematoda) Roundworms (Nematoda)
False coelom (pseudocoelom) Complete digestive system(one way gut) Sexes separate pharynx intestine eggs in uterus gonad anus false coelom muscularized body wall Fig. 25-27, p.419 Annelids: Phylum Annelida
SEGMENTED, COELOMATE WORMS SEGMENTED, COELOMATE WORMS Closed circulatory system,most life functions on an organ system level Arthropods: Arthropods: Phylum Arthropoda The phylum with the greatest number of species Four lineages:
– Trilobites (all extinct) – Chelicerates (spiders, mites, scorpions) – Crustaceans (crabs, shrimps, barnacles) – Uniramians (insects, centipedes, millipedes) ADAPTATIONS FOR SUCCESS Hardened exoskeleton Jointed appendages Fused and modified segments Respiratory structures Specialized sensory structures Division of labor Chelicerates and Crustaceans Chelicerates and Crustaceans Originated in seas A few are still marine: horseshoe crabs, sea spiders The arachnids are all terrestrial
Spiders, Mites,Scorpions, Chiggers, Ticks “Daddy longlegs” Most are marine, some freshwater, a few terrestrial Head has two pairs of antenna, three pairs of foodhandling appendages Chelicerates and Crustaceans Chelicerates and Crustaceans Millipedes and Centipedes Millipedes and Centipedes Segmented bodies with many legs Millipedes – Two pairs of legs per “segment” – Scavengers Centipedes – Flattened, with one pair of legs per segment – Predators Insect Diversity Insect Diversity The only winged invertebrates More than 800,000 known species Most successful species are small in size and have a great reproductive capacity Insect Body Plan Insect Body Plan Thorax usually has three pairs of legs and one or two pairs of wings Abdomen contains most internal organs and specialized structure for reproduction Threepart gut Malpighian tubules attach to midgut and serve in elimination of metabolic wastes Open circulatory system (hemocoel) Types of Insect Development
Different stages exploit different resources at different times Growth and molting egg young adult Incomplete metamorphosis egg Complete metamorphosis nymphs adult egg larvae pupa adult Fig. 25-36, p.424 Echinoderms Echinoderms DEUTEROSTOMES Body wall has spines or plates No brain Adults are radial with bilateral features Water vascular system Sea urchin Sea cucumber Brittle star Body Plan of a Sea Star Body Plan of a Sea Star
sieve plate anus upper stomach lower stomach digestive gland eyespot gonad coelom Figure 25.44a Page 429 ...
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