Chapter 24 Animal Evolution – The Invertebrates Sections 1-7

1. Chapter 24Animal Evolution –The InvertebratesSections 1-7

2. 24.2 Animal Traits and Body Plans • Animals are multicelled heterotrophs that move about during part or all of the life cycle • Their body cells do not have a wall and are typically diploid • Gametes are the only haploid stage in an animal life cycle

3. Major Animal Phyla Sponges Cnidarians Flatworms Annelids Mollusks Roundworms Arthropods Echinoderms Chordates Molting Trochophore Larva Deuterostome Development Protostome Development Radial Symmetry Bilateral Symmetry Tissues Multicellularity

4. Animal Body Plans: Organization • The most ancient animal lineages such as sponges are organized as aggregations of cells • Most animal cells are organized as tissues consisting of one or more cell types organized to perform a specific function • Tissue formation begins in an embryo • Some have two tissue layers: ectoderm and endoderm • Later lineages also have middle layer: mesoderm

5. 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

6. Gut and Body Cavity • Most animals have a gutthat opens at the body surface • Digestive sac (incomplete digestive system) • Digestive tube (complete digestive system) • Typically, a body cavity surrounds the gut • Coelom: Cavity lined by mesodermal tissue • Pseudocoelom: Cavity is partially lined • Acoelomates have no body cavity

7. epidermis (from ectoderm) tissues, organs (from mesoderm) gut tissue (from endoderm) gut cavity A Acoelomate body plan of a flatworm. Figure 24-3a p395

8. coelom epidermis (from ectoderm) tissues, organs (from mesoderm) gut tissue (from endoderm) gut cavity B Coelomate body plan of an earthworm. Figure 24-3b p395

9. pseudocoelom epidermis (from ectoderm) tissues, organs (from mesoderm) gut tissue (from endoderm) gut cavity C Pseudocoelomate body plan of a roundworm. Figure 24-3c p395

10. Two Lineages of Bilateral Animals • Protostomes • Blastopore in the embryo becomes the mouth • Second opening becomes the anus • Deuterostomes • Blastopore in the embryo becomes the anus • Second opening becomes the mouth

11. Take-Home Message:What are animals? • Animals are multicelled heterotrophs with unwalled, typically diploid cells; animals are motile for part or all of their life • Early animals had an asymmetrical body plan. Later, radially symmetrical and then bilaterally symmetrical bodies evolved • Most bilaterally symmetrical animals have a fluid-filled coelom • The two lineages of bilaterally symmetrical animals, protostomes and deuterostomes, differ in development, but both develop from an embryo that has three tissue layers

12. Colonial Origins • Animals probably evolved from a colonial, choanoflagellate-like protist • Choanoflagellates (“collared flagellate”) are the modern protists most closely related to animals • A collar of microvilli surrounds the flagellum • They have proteins similar to adhesion or intercellular signaling proteins in animals

13. The Cambrian Explosion • Animals underwent a dramatic adaptive radiation during the Cambrian (542–488 million years ago) • By the end of this period, all major animal lineages were present in the seas • Contributing factors include increased oxygen levels, movement of landmasses, and evolution of homeotic genes

14. Take-Home Message: Animal origins and diversification • Animals probably evolved from a colonial protist that resembled modern choanoflagellates • Biomarkers characteristic of sponges have been found in rocks that date back more than 635 million years • Some representatives of modern animal lineages are found among the Ediacarans • A great adaptive radiation of animals took place during the Cambrian period

15. 24.4 The Sponges • Sponges (phylum Porifera) • Sessile animalsthat attach to seafloor or other surfaces • No symmetry, tissues, or organs • Fibrous proteins and glassy silica spikes provide structure and discourage predation • Pores with flagellated collar cells filter water • Digestion is intracellular • Amoeboid cells in the jellylike matrix receive nutrients from collar cells and distribute them through the body

16. Take-Home Message:What are sponges? • Sponges are mostly marine animals that have an asymmetrical body without any tissues or organs • Ciliated larvae swim briefly, but adults are sessile filter feeders that strain bits of food from water flowing through their pores

17. 24.5 Cnidarians—True Tissues • Cnidarians(phylum Cnidaria) • Radial animals with two tissue layers • A tentacle-ringed orifice opens onto a gastrovascular cavitythat functions in digestion and gas exchange • Two cnidarian body plans: • Medusae (jellyfishes) are bell shaped and drift • Polyps(sea anemones) are tubular with one end usually attached to a surface

18. Two Cnidarian Body Plans gastrovascular cavity outer epithelium (epidermis) mesoglea (matrix) inner epithelium (gastrodermis) gastrovascular cavity

19. reproductive polyp female medusa male medusa 6 ovum sperm 1 zygote feeding polyp 5 2 3 4 one branch of a colony growth of a polyp ciliated bilateral larva Stepped Art Figure 24-9b p399

20. Anthozoans • Anthozoans such as corals and sea anemones have no medusa stage • Gametes form on polyps • Coral reefs are colonies of polyps that enclose themselves in secreted calcium carbonate • Photosynthetic dinoflagellates live in the polyp’s tissues and provide it with sugars

21. Take-Home Message:What are cnidarians? • Cnidarians are radial, mostly marine predators with two tissue layers; there are two body plans: medusa and polyp • Tentacles with cnidocytes surround a mouth that opens onto a gastrovascular cavity; a nerve net interacts with the hydrostatic skeleton to allow movement • Cnidarians include sea anemones, jellies, and corals; reef-building corals secrete the calcium carbonate that forms reefs

22. 24.6 Flatworms—Simple Organ Systems • Flatworms(phylum Platyhelminthes) have a three-layer embryo that develops into an adult with many organ systems but no coelom • Three main classes: turbellarians, flukes (trematodes), and tapeworms (cestodes)

23. Structure of a Free-Living Flatworm • Planarians, a free-living flatworm • Propelled by cilia that cover their body surface • A pharynx sucks food into a highly branched gastrovascular cavity • Nutrients and oxygen diffuse to body cells • Chemical receptors and two light-detecting eyespots • Simple brain consisting of paired ganglia • Nerve cordsrun the length of the body • Reproduce sexually or asexually • Tubules with flame cells regulate water and solute levels

24. ovary testis oviduct genital pore Figure 24-12c p400

25. Parasites: Flukes and Tapeworms • Blood flukes (Schistosoma) • Reproduction takes place in mammals • Immature stages live in intermediate hosts (snails) • Tapeworms • Live and reproduce in the vertebrate gut • Body consists of proglottids – repeating hermaphroditic body units behind a hooked scolex

26. 1 proglottid scolex 2 beef with larval tapeworm tapeworm in cattle muscle 5 4 3 proglottid with fertilized eggs larva Stepped Art Figure 24-13 p401

27. Take-Home Message:What are flatworms? • Flatworms are bilateral, acoelomate animals with a gastrovascular cavity, a cephalized nervous system, and a system for regulating water and solutes • Free-living flatworms include marine species and freshwater planarians • Flukes and tapeworms are parasitic flatworms; both groups include species that infect humans

28. 24.7 Annelids—Segmented Worms • Annelids (phylum Annelida) are bilateral worms with a coelom, a closed circulatory system, and a segmented body; typically with chaetae (chitin reinforced bristles) • Three main groups: marine worms (polychaetes), oligochaetes (including earthworms), and leeches

29. Leeches – Bloodsuckers and Others • Leeches lack bristles and have a sucker at either end • Many are scavengers or predators of small invertebrates • Some attach to a vertebrate, pierce its skin, and suck blood –their saliva has a protein that keeps blood from clotting

30. Earthworm – An Oligochaete • Earthworms: • Body is segmented inside and out • Fluid-filled coelom is divided into chambers • Exchange gases across body surfaces • Have five hearts and a closed circulatory system • Complete digestive system • Nephridia regulate coelomic fluid • Nervous system of ganglia and nerve cords • Hydrostatic skeleton • Hermaphroditic

31. anus secretory region (clitellum) intestine gizzard crop esophagus pharynx longitudinal muscle mouth ventral nerve cord circular muscle brain 2 of 5 hearts Figure 24-16a1 p403

32. excretory organ dorsal blood vessel fluid-filled coelom gut ventral blood vessel ventral nerve cord Figure 24-16a2 p403

33. Chapter 24Animal Evolution –The InvertebratesSections 8-15

34. 25.8 Mollusks—Animals With a Mantle • Mollusks (phylum Mollusca) • Bilaterally symmetrical with a reduced coelom • Mantlecovers internal organs, secretes a shell • Gills for respiration in aquatic species • Feed using a hard radula • Have a complete digestive tract

35. gill excretory organ anus heart mantle cavity digestive gland stomach shell edge of mantle that covers organs foot radula Figure 24-18a p404

36. Mollusk Diversity • Chitons • Eight overlapping plates • Gastropods(snails, slugs) • Undergo torsion during development • Include the only terrestrial mollusks • Bivalves(mussels, clams, oysters) • Hinged, two-part shell • Cephalopods (squids, octopuses) • Large, fast and smart; closed circulatory system

37. Terrestrial Gastropods • In land-dwelling snails and slugs, a lung replaces the gill • Glands on the foot secrete mucus that protects the animal as it moves across dry, abrasive surfaces • Land-dwellers tend to be hermaphrodites; the embryos of these groups develop directly into adults

38. Bivalve Body Plan: Clam adductor muscle (cut) mouth left mantle adductor muscle (cut) Water flows out through exhalant siphon Water flows in through inhalant siphon foot palps left gill shell

39. Cephalopods • Cephalopod (“head foot”) • Tentacles attached to the head are evolutionary modifications of the foot; they surround the mouth, which has a hard, horny beak • Include the fastest (squids), biggest (giant squid), and smartest (octopuses) invertebrates • Jet propulsion, complex eyes, closed circulatory system, complex behavior

40. Cephalopod: Octopus

41. Take-Home Message:What are mollusks? • Mollusks are invertebrates with a bilateral body plan, a reduced coelom, and a mantle that drapes over their internal organs. In most species, the mantle secretes a protective hardened shell • Most mollusks are aquatic, but some gastropods have adapted to life on land • In addition to gastropods, mollusks include chitons, bivalves, and cephalopods

42. 24.10 Roundworms:Unsegmented Worms That Molt • Roundworms (phylum Nematoda) are unsegmented, pseudocoelomate worms with a secreted cuticle that is molted • Most are decomposers, some are parasites • Human parasites include Ascaris (intestinal roundworm), Wuchereria (elephantiasis), and Enterobius (pinworms) • Roundworms also affect livestock, pets, and crop plants

43. Roundworm Body Plan pharynx intestine eggs in uterus gonad false coelom (unlined body cavity) muscular body wall anus

44. Roundworms That Infect Humans

45. 24.11 Arthropods: • Arthropods(phylum Arthropoda) are the most diverse animal phylum, with more than a million species • Bilateral, with a reduced coelom • Hard, jointed external skeleton • Complete digestive system; open circulatory system; respiratory and excretory organs • Sexes are usually separate; some hermaphrodites • Modern arthropods include horseshoe crabs, spiders, ticks, crabs, lobsters, centipedes, and insects

46. Key Arthropod Adaptations • A hardened exoskeleton (cuticle) • Hormones control molting • Jointed appendages for movement • Some legs are modified for special tasks • Highly modified segments • Example: wings

47. Key Arthropod Adaptations (cont.) • Sensory specializations • Compound eyes • Antennae that detect touch and chemicals • Specialized developmental stages • Body plans may change by metamorphosis • Example: Caterpillar and butterfly

48. Molting An Old Exoskeleton.

49. Take-Home Message: What factors contribute to arthropod success? • Arthropods are the most diverse animal phylum; in addition to modern groups, they include the extinct trilobites • A hardened exoskeleton protects the body and prevents water loss on land; the exoskeleton is molted as the animal grows, and it is thin at joints to allow movement; sensory specializations include antennae and compound eyes • In many groups, larvae differ from adults in body form and utilize different resources

50. Chelicerate Structure • Chelicerates • Body with two regions, a cephalothorax (fused head and thorax) and an abdomen • Walking legs attach to the cephalothorax • Head has eyes, but no antennae • Paired feeding appendages near the mouth (chelicerae)