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Animal Evolution –The Invertebrates. Chapter 25 Part 1. Impacts, Issues Old Genes, New Drugs. Humans and other vertebrates share genes with invertebrates, including the cone snail – which makes powerful conotoxins. 25.1 Animal Traits and Body Plans. Animals
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Animal Evolution –The Invertebrates Chapter 25 Part 1
Impacts, IssuesOld Genes, New Drugs • Humans and other vertebrates share genes with invertebrates, including the cone snail – which makes powerful conotoxins
25.1 Animal Traits and Body Plans • Animals • Multicelled heterotrophs that move about during part or all of the life cycle • Body cells do not have a wall and are typically diploid • The overwhelming majority are invertebrates
Animal Body Plans: Organization • Tissues • Cells of a particular type and function, organized in a specific pattern • Tissue formation begins in an embryo • Ectoderm and endoderm • Mesoderm
Tissue Formation • Formation of a three-layer animal embryo
ectoderm mesoderm endoderm Fig. 25-2, p. 404
Animal Body Plans: Body Symmetry • Body Symmetry • Simplest animals are asymmetrical (sponges) • Jellyfish and hydras have radial symmetry • Most animals have bilateral symmetry • Cephalization • In most bilateral animals, nerve cells are concentrated at the head end
posterior anterior Fig. 25-3, p. 405
Animal Body Plans: Gut and Body Cavity • Gut • Digestive sac (incomplete digestive system) or tube (complete) that opens at the body surface • Typically, a body cavity surrounds the gut • Coelom: Cavity lined by mesodermal tissue • Pseudocoel: Cavity is partially lined • Acoelomates have no body cavity
epidermis gut cavity organs packed between gut and body wall A No coelom (acoelomate animal) Fig. 25-4a, p. 405
epidermis gut cavity B Pseudocoel (pseudocoelomate animal) unlined body cavity around gut Fig. 25-4b, p. 405
gut cavity epidermis C Coelom (coelomate animal) body cavity with a lining (dark blue) derived from mesoderm Fig. 25-4c, p. 405
Two Lineages of Bilateral Animals • Protostomes • First opening in the embryo becomes the mouth • Second opening becomes the anus • Deuterostomes • First opening in the embryo becomes the anus • Second opening becomes the mouth
Animal Body Plans: Circulation • In small animals, gases and nutrients diffuse through the body • Most animals have a circulatory system • Closed circulatory system: Heart pumps blood through a continuous vessel system • Open circulatory system: Blood leaves the vessels
Animal Body Plans: Segmentation • Many bilateral animals are segmented • Similar units repeated along length of body • Repetition allows evolution of specialization
25.2 Animal Origins and Adaptive Radiation • Fossils and gene comparisons among modern species provide insights into how animals arose and diversified
Becoming Multicellular • Animals probably evolved from a colonial, choanoflagellate-like protist • Choanoflagellates (“collared flagellate”) • Modern protists most closely related to animals • A collar of microvilli surrounds the flagellum • Have proteins similar to adhesion or intercellular signaling proteins in animals
amoebozoans fungi choanoflagellates animals Fig. 25-5c, p. 406
A Great Adaptive Radiation • Animals underwent a dramatic adaptive radiation during the Cambrian
Relationships and Classification • Animals have traditionally been classified based on morphology and developmental pattern • Mainly features of body cavities • A newer system puts all animals with a three-layer embryo into protostomes or deuterostomes • Protostomes are divided into animals that molt (Ecdysozoa) and don’t molt (Lophotrochozoa)
chordates Deuterostomes echinoderms arthropods tardigrades Protostomes annelids mollusks Coelomate animals rotifers Pseudocoelomate animals roundworms flatworms Acoelomate animals Animals with a 3-layer embryo cnidarians Animals with tissues sponges Animals placozoans Fig. 25-7a, p. 407
Deuterostomes chordates echinoderms arthropods Ecdysozoa tardigrades roundworms Protostomes rotifers mollusks Lophotrochozoa annelids flatworms Animals with a 3-layer embryo cnidarians Animals with tissues sponges placozoans Animals Fig. 25-7b, p. 407
25.1-25.2 Key ConceptsIntroducing the Animals • Animals are multicelled heterotrophs that actively move about during all or part of the life cycle • Early animals were small and structurally simple • Their descendants evolved a more complex structure and greater integration among specialized parts
25.3 The Simplest Living Animal • Placozoans, the simplest known animals, have no body symmetry, no tissues, and just four different types of cells • Example: Trichoplax adherens
25.4 The Sponges • Sponges are simple but successful; they have survived in seas since Precambrian times • Sponges (phylum Porifera) • Attach to seafloor or other surfaces • No symmetry, tissues, or organs • Pores with flagellated collar cells filter water • Sexual or asexual reproduction
water out glassy structural elements amoeboid cell pore semifluid matrix central cavity flattened surface cells collar cell water in water in flagellum collar of microvilli nucleus Fig. 25-10, p. 409
Sponge Reproduction and Dispersal • Hermaphrodite • Individual that produces both eggs and sperm • Sperm are released into water; eggs are retained • Zygote develops into ciliated larva • Larva • Free-living, sexually immature stage in life cycle • Settles and develops into adult
Sponge Characteristics • Toxins and fibrous or sharp body parts deter predators • Some freshwater sponges survive unfavorable conditions by producing gemmules • Sponges show cell adhesion, self-recognition
25.5 Cnidarians—True Tissues • Cnidarians (phylum Cnidaria) • Radial animals with two tissue layers • Medusae (jellyfishes) are bell shaped and drift • Polyps (sea anemones) are tubular with one end usually attached to a surface • Four classes: hydrozoans, anthozoans, cubozoans, and scyphozoans
gastrovascular cavity outer epithelium (epidermis) mesoglea (matrix) inner epithelium (gastrodermis) gastrovascular cavity Fig. 25-11, p. 410