The Animal Kingdom An Introduction to Animal Diversity

The Animal Kingdom: An Introduction to Animal Diversity Chapter 29

Learning Objective 1 • What characters are common to most animals?

Kingdom Animalia • • Eukaryotic Multicellular Heterotrophic Cells specialized for specific functions

Structure • Body plan • • basic structure and functional design of body Animals have diverse body plans

Function • Most animals • • • are capable of locomotion at some time during life cycle can respond adaptively to external stimuli can reproduce sexually

Sexual Reproduction • Sperm and egg unite (zygote) • Zygote undergoes cleavage • cell divisions produce hollow ball of cells (blastula) • • Blastula undergoes gastrulation • forms embryonic tissues

KEY CONCEPTS • Animals are multicellular, eukaryotic heterotrophs

Explore the characteristics of animals by clicking on the figures in Thomson. NOW.

Learning Objective 2 • Compare the advantages and disadvantages of life in the ocean, in fresh water, and on land

Marine Environments • Provide • • Fluid and salt balance • • relatively stable temperatures buoyancy readily available food more easily maintained than in fresh water Disadvantages: • currents and other water movements

Fresh Water • Provides • • • less constant environment less food Animals must osmoregulate • fresh water is hypotonic to tissue fluid

Terrestrial Animals • Have adaptations that • • • protect them from drying out protect them from temperature changes protect their gametes and embryos

Marine and Terrestrial Environments

Learning Objective 3 • Use current hypotheses to trace the early evolution of animals

Hypotheses • Proterozoic eon • • • most animal clades diverged over long period based on molecular data Cambrian Radiation • • new body plans rapidly evolved among clades first fossils of these animals

Hox Genes • Hox gene group • • controls early development in animal groups Cambrian period • • many Hox genes had evolved mutations could have resulted in rapid changes in animal body plans

Learning Objective 4 • How do biologists use structural characters (variations in body symmetry, number of tissue layers, type of body cavity) and patterns of early development to infer relationships among animal phyla?

Symmetry • Cnidarians and ctenophores are closely related • • • because they share radial symmetry most other animals exhibit bilateral symmetry Cephalization (development of head) • evolved with bilateral symmetry

Radial and Bilateral Symmetry

Radial symmetry (top view) Fig. 29 -3 a, p. 623

Radial symmetry (side view) Fig. 29 -3 b, p. 623

Dorsal Frontal section Caudal Posterior Anterior Cephalic Ventral Cross (or transverse) section Bilateral symmetry (lateral view) Fig. 29 -3 c, p. 623

Dorsal Sagittal section Medial Frontal section Lateral Ventral Bilateral symmetry (front view) Fig. 29 -3 d, p. 623

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Other Structural Characters • Relationships can be based on • • • level of tissue development type of body cavity Embryonic tissues (germ layers)

Coelom Formation

Schizocoely — characteristic of protostomes Enterocoely — characteristic of deuterostomes Ectoderm Developing mesoderm Blastopore Ectoderm Presumptive mesoderm Enterocoelic pouch Endoderm Mesoderm Ectoderm Developing coelom (Schizocoel) Ectoderm Endoderm Gut Ectoderm Endoderm Mesoderm Gut Coelom (Enterocoel) Coelom Mesoderm Gut Endoderm Mesentery Epidermis (ectoderm) Coelom Muscle layer (mesoderm) Gut Peritoneum (mesoderm) Fig. 29 -6, p. 626

Schizocoely — characteristic of protostomes Enterocoely — characteristic of deuterostomes Ectoderm Developing mesoderm Blastopore Ectoderm Presumptive mesoderm Enterocoelic pouch Endoderm Mesoderm Ectoderm Endoderm Gut Ectoderm Endoderm Developing coelom (Schizocoel) Mesoderm Coelom (Enterocoel) Gut Coelom Mesoderm Gut Endoderm Mesentery Epidermis (ectoderm) Coelom Muscle layer (mesoderm) Peritoneum (mesoderm) Gut Stepped Art Fig. 29 -6, p. 626

Germ Layers • Outer layer (ectoderm) • • Inner layer (endoderm) • • gives rise to body covering, nervous system lines the gut and other digestive organs Middle layer (mesoderm) • gives rise to most other body structures

Body Plans

Epidermis (from ectoderm) Muscle layer (from mesoderm) Mesenchyme (gelatin-like tissue) Epithelium (from endoderm) (a) Acoelomate—flatworm (liver fluke). Fig. 29 -4 a, p. 624

Pseudocoelom Epidermis (from ectoderm) Muscle layer (from mesoderm) Epithelium (from endoderm) (b) Pseudocoelomate—nematode. Fig. 29 -4 b, p. 624

Coelom Epidermis (from ectoderm) Muscle layer (from mesoderm) Peritoneum (from mesoderm) Epithelium (from endoderm) Mesentery (from mesoderm) (c) True coelomate—vertebrate. Fig. 29 -4 c, p. 624

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Bilateral Symmetry • Acoelomate • • Pseudocoelomate • • no body cavity not completely lined with mesoderm Coelomate, (animal with true coelom) • body cavity completely lined with mesoderm

Bilateral Animals • Two major evolutionary branches: • Protostomia • • mollusks, annelids, arthropods Deuterostomia • echinoderms, chordates

Blastopore • Opening from embryonic gut to outside • In protostomes • • develops into the mouth In deuterostomes • becomes the anus

Cleavage 1 • Protostomes • • • undergo spiral cleavage early cell divisions diagonal to polar axis Deuterostomes • • • undergo radial cleavage early cell divisions either parallel or at right angles to polar axis cells lie directly above or below one another

Spiral and Radial Cleavage

Polar axis Top view Spiral cleavage Fig. 29 -5 a, p. 625

Polar axis Top view Radial cleavage Fig. 29 -5 b, p. 625

Cleavage 2 • Protostomes • • • undergo determinate cleavage fate of each embryonic cell is fixed very early Deuterostomes • • undergo indeterminate cleavage fate of each embryonic cell is more flexible

Relationships Based on Structure

Parazoa Eumetazoa Bilateria Echinodermata Coelomates Chordata Hemichordata Mollusca Annelida Deuterostomia Arthropoda Onychophora Tardigrada Rotifera Nematoda Nemertea Platyhelminthes Ctenophora Cnidaria Acoelomates Pseudocoelomates Protostomia Porifera Choanoflagellates Radiata Segmentation Pseudocoelom Deuterostome development True coelom Radial symmetry Protostome development Three tissue layers (mesoderm) Bilateral symmetry Tissues (ectoderm and endoderm) Multicellularity Choanoflagellate ancestor Fig. 29 -7, p. 627

KEY CONCEPTS • Biologists classify animals based on their body plan and features of their early development

Learning Objective 5 • What are three major contributions to animal phylogeny made by molecular systematics? • Identify the three major clades of bilateral animals

Molecular Systematics 1 • Confirmed much of animal phylogeny based on structural characters • including axiom that animal body plans usually evolved from simple to complex

Molecular Systematics 2 • Provided evidence for exceptions to “simple-to-complex” rule • Example • molecular data indicate flatworms and ribbon worms evolved from more complex animals, became simpler over time

Molecular Systematics 3 • Molecular data suggest pseudocoelomate animals do not form natural group • probably evolved from coelomate ancestors

Protostomes • 2 clades based on molecular data: • Lophotrochozoa • • flatworms, ribbon worms, mollusks, annelids, lophophorate phyla, rotifers Ecdysozoa (animals that molt) • nematodes and arthropods

3 Clades of Bilateral Animals Lophotrochozoa • • • Ecdysozoa Deuterostomia

Relationships Based on Molecular Data

Parazoa Eumetazoa Bilateria Chordata Hemichordata Arthropoda Onychophora Tardigrada Nematoda Rotifera Lophophorate phyla Annelida Mollusca Nemertea Platyhelminthes Ctenophora Cnidaria Ecdysozoa Lophotrochozoa Echinodermata Deuterostomia Protostomia Porifera Choanoflagellates Radiata Segmentation Protostome pattern of development Radial symmetry Deuterostome pattern of development Bilateral symmetry, three tissue layers, body cavity Tissues Multicellularity Choanoflagellate ancestor Fig. 29 -8 a, p. 629

Choanoflagellate ancestor Fig. 29 -8 b, p. 629 Deuterostomia Ecdysozoa Lophotrochozoa Radiata Parazoa

KEY CONCEPTS • Molecular data indicate that bilateral animals split into three major clades: • two protostome groups—Lophotrochozoa (such as flatworms, mollusks, and annelids) and Ecdysozoa (such as nematodes and arthropods)—and deuterostomes (echinoderms and chordates)

Learning Objective 6 • What are the distinguishing characteristics of phylum Porifera?

Phylum Porifera • Sponges • • animals characterized by flagellate collar cells (choanocytes) The only members of the Parazoa • sister group of Eumetazoa

Sponge Structure • Sponge body • • sac with tiny openings for water to enter central cavity (spongocoel) open end (osculum) for water to exit Sponge cells • • loosely associated do not form true tissues

Sponge Structure

Deuterostomia Ecdysozoa Lophotrochozoa Radiata Porifera Parazoa Choanoflagellate ancestor Fig. 29 -9 a, p. 630

Incurrent pores Water movement Osculum Spongocoel Epidermal cell Porocyte Spicule Flagellum Microvillus Nucleus Collar cell Amoeboid cell in mesohyl Collar Fig. 29 -9 b, p. 630

KEY CONCEPTS • Sponges (phylum Porifera) are characterized by collar cells and by loosely associated cells that do not form true tissues

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Learn more about sponge structure by clicking on the figure in Thomson. NOW.

Learning Objective 7 • What are the distinguishing characteristics of phylum Cnidaria? • Describe four classes of this phylum • Give examples of animals that belong to each class

Phylum Cnidaria 1 • Characterized by • • • radial symmetry two tissue layers cnidocytes (cells containing nematocysts)

Nematocysts

Cnidocyte Nucleus Thread Capsule Nematocyst (not discharged) Cnidocil (trigger) Thread Nematocyst (discharged) Fig. 29 -11 b, p. 634

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Phylum Cnidaria 2 • Gastrovascular cavity • • with single opening for mouth and anus Nerve cells form irregular, nondirectional nerve nets • connect sensory cells with contractile and gland cells

Cnidarian Structure • Hydra

Tentacles Cnidocytes (stinging cells) 1 mm Mouth Bud Gastrovascular cavity Epidermis Mesoglea Gastrodermis Egg (ovum) Ovary Fig. 29 -12, p. 634

Cnidaria Life Cycle • Sessile polyp stage • • form with dorsal mouth surrounded by tentacles Free-swimming medusa (jellyfish) stage

Cnidaria Life Cycle • Obelia

1 Reproductive polyps produce medusae by budding asexually Mouth Tentacle Medusae Feeding polyp Medusa bud Reproductive polyp Gastrovascular cavity Egg 2 Free-swimming medusae reproduce sexually. Sperm Planula larva 3 Zygote develops into ciliated planula larva. Polyp colony 5 Colony grows as new polyps bud and remain attached. (b) Life cycle of Obelia. Young polyp colony 4 Larva develops into polyp that forms new colony. Fig. 29 -13 b, p. 635

4 Classes of Phylum Cnidaria 1. Class Hydrozoa (hydras, hydroids, Portuguese man-of-war) • • typically polyps may be solitary or colonial 2. Class Scyphozoa (jellyfish) • generally medusae

4 Classes of Phylum Cnidaria 3. Class Cubozoa (“box jellyfish”) • have complex eyes that form blurred images 4. Class Anthozoa (sea anemones, corals) • • • polyps may be solitary or colonial differ from hydrozoans in organization of gastrovascular cavity

Cnidarians

Deuterostomia Ecdysozoa Lophotrochozoa Ctenophora Cnidaria Parazoa Radiata Choanoflagellate ancestor Fig. 29 -10 (1), p. 633

Mouth Epidermis Mesoglea Gastrodermis Gastrovascular cavity Class Hydrozoa (polyp) Fig. 29 -10 a, p. 633

Mouth Mesoglea Gastrodermis Epidermis Gastrovascular cavity Class Scyphozoa (medusa) Fig. 29 -10 b, p. 633

Mouth Epidermis Mesoglea Gastrodermis Gastrovascular cavity Class Anthozoa (polyp) Fig. 29 -10 c, p. 633

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KEY CONCEPTS • Members of phylum Cnidaria (hydras, jellyfish, sea anemones) are characterized by radial symmetry, two tissue layers, and cnidocytes, cells that contain stinging organelles

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Learn more about cnidarian body forms, nematocysts, and life cycles by clicking on the figures in Thomson. NOW.

Learning Objective 8 • What are the distinguishing characteristics of phylum Ctenophora?

Phylum Ctenophora • Comb jellies • • fragile, luminescent marine predators biradial symmetry eight rows of cilia that resemble combs tentacles with adhesive glue cells

Comb Jelly

KEY CONCEPTS • Members of phylum Ctenophora (comb jellies) have biradial symmetry, two tissue layers, eight rows of cilia, and tentacles with adhesive glue cells