Animal Diversity: Key Features, Anatomical Branch Points, and Major Phyla

1. Chapter 23 Animal Diversity I: Invertebrates

2. Chapter 23 At a Glance • 23.1 What Are the Key Features of Animals? • 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? • 23.3 What Are the Major Animal Phyla?

3. 23.1 What Are the Key Features of Animals? • Animals possess all of the following characteristics • Eukaryotes(真核生物) • Multicellularity (多细胞) • Their cells lack a cell wall(无细胞壁) • They obtain energy by consuming other organisms(吃) • Most reproduce sexually (有性生殖) • They are motile at some point in the life cycle(运动 ) • They are able to respond rapidly to external stimuli(反应快)

4. 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? • Most animal phyla that currently populate Earth were present by the Cambrian(寒武纪) period (544 million years ago) • The scarcity of pre-Cambrian fossils led systematists to search for clues about the evolutionary history of animals by examining features of: • Anatomy • Embryological development • DNA sequences

5. 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? • Certain features represent evolutionary milestones, and mark major branching points on the animal evolutionary tree • The appearance of tissues (组织) • The appearance of body symmetry (躯体对称性) • Protostome(原口动物) and deuterostome(后口动物) development

6. An Evolutionary Tree of Some Major Animal Phyla Fig. 23-1

7. 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? • Animals with radial symmetry can be divided into roughly equal halves by any plane that passes through the central axis • Animals with radial symmetry have two embryonic tissue (germ) layers(胚层) • Ectoderm(外胚层), which is an outer layer that covers the body, lines its inner cavities, and forms the nervous system • Endoderm(内胚层), which is an inner layer that lines most hollow organs • Bilaterally symmetrical animals have three embryonic tissue (germ) layers • A layer of mesoderm(中胚层) between the ectoderm and endoderm forms muscles, and the circulatory and skeletal systems

9. 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? • Bilaterally symmetrical animals have heads • Animals with bilateral symmetry can be divided into mirror-image halves only along one plane that runs down the midline • These animals exhibit cephalization(头部化), the concentration of sensory organs and a brain in a well-defined head, with definite anterior (head) and posterior (which may feature a tail) regions

10. Body Symmetry and Cephalization central axis anterior plane of symmetry plane of symmetry posterior (a) Radial symmetry (b) Bilateral symmetry Fig. 23-2

12. 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? • Most bilateral animals have body cavities(体腔) • Body cavities are fluid-filled cavities between the digestive tube and the outer body wall • Body cavities have a variety of functions • They can act as a skeleton, providing support for the body and a framework against which muscles can act • They can form a protective buffer between the internal organs and the outside world • They can allow organs to move independently of the body wall

13. Body Cavities The body cavity is completely lined with tissue derived from mesoderm The body cavity is partially, but not completely, lined with tissue derived from mesoderm There is no cavity between the body wall and digestive tract body wall body wall body wall pseudocoelom coelom digestive tract digestive tract digestive tract digestive cavity digestive cavity digestive cavity (a) “True” coelom (annelids, chordates) (b) “False” or pseudocoelom (roundworms) (c) No coelom (cnidarians, flatworms) Fig. 23-3

14. 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? • Bilateral organisms develop in one of two ways based on embryological development • Protostome(原口动物) development • In these animals, the body cavity forms within the space between the body wall and the digestive cavity • These animals include nematodes, arthropods, annelids, and mollusks • Deuterostome(后口动物) development • In these animals, the body cavity forms as an outgrowth of the digestive cavity • Echinoderms and chordates are deuterostomes

15. 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? • Protostomes include two distinct evolutionary lines • Ecdysozoans(退皮动物) • Bodies are covered by an outer layer that is periodically shed • Examples include the arthropods and roundworms • Lophotrochozoans (冠轮动物) • This group has a lophophore(触手冠) (a special feeding structure) as well as a phyla that passes through a trochophore(担轮幼虫) larva developmental stage • Examples include mollusks, annelids, and flatworms

16. 23.3 What Are the Major Animal Phyla? • Animals probably originated from ancestral colonial protists • Present day biologists recognize about 27 phyla of animals • Most animals are invertebrates (lack a vertebral column) • Less than 3% of all known animals are vertebrates (possess a vertebral column)

17. 23.3 What Are the Major Animal Phyla? • Sponges have a simple body plan • Sponges belong to the phylum Porifera(海绵动物门) and are found in most marine and aquatic environments • Sponges do not move, but occur in a variety of sizes and shapes • They may reproduce asexually by budding(出芽), where the adult produces miniature versions of itself that drop off and assume an independent existence • They may reproduce sexually through fusion of sperm and eggs

18. The Diversity of Sponges Fig. 23-4

19. 23.3 What Are the Major Animal Phyla? • Sponges lack true tissues and organs • The sponge body is perforated by tiny pores through which water passes, and by fewer, large openings through which water is expelled • As water passes through the sponge, oxygen is extracted, and microorganisms are filtered out and digested by individual cells

20. 23.3 What Are the Major Animal Phyla? • Sponge cells are specialized for different functions • Epithelial cells(上皮细胞) are flat cells that cover the outer body surface • Pore cells (孔细胞)are modified epithelial cells that regulate the flow of water through pores • Collar cells(领细胞) are flagellated cells that maintain water flow through the sponge • Amoeboid cells (变形细胞)are motile cells that digest and distribute nutrients, produce reproductive cells, and secrete skeletal projections called spicules (骨针)

21. The Body Plan of Sponges (water flow out of the sponge) epithelial cell pore spicules (water flow into the sponge) amoeboid cell pore cell collar cell (water flow) Fig. 23-5

22. 23.3 What Are the Major Animal Phyla? • Cnidarians are well-armed predators • Sea jellies, sea anemones, corals, and hydrozoans belong to the phylum Cnidaria(腔肠动物门) • These animals are mostly marine and are all carnivorous predators(肉食动物) • The cells of cnidarians are arranged into distinct tissues, including a contractile muscle-like tissue and an organized nerve net

23. 23.3 What Are the Major Animal Phyla? • Cnidarians are well-armed predators (continued) • The nerve net(网络状神经系统) of cnidarians branches throughout the body and controls the contractile tissue to bring about movement and feeding behavior • Most cnidarians lack true organs and have no brain

24. Cnidarian Diversity Fig. 23-6

25. 23.3 What Are the Major Animal Phyla? • Cnidarians have two body plans: the polyp(水螅型) and the medusa(水母型) • Many species have life cycles that include both body plans • Polyps and medusae develop from two germ layers—the endoderm and the ectoderm—with a jelly-like substance between the layers • The polyp is attached to rocks, while the medusa floats in the water; both have tentacles with cnidocytes(刺细胞), specialized cells that function in defense and the capture of prey

26. Polyp and Medusa lining of gastrovascular cavity lining of gastrovascular cavity mouth gastrovascular cavity tentacle body wall body wall tentacle gastrovascular cavity foot mouth (a) Polyp (b) Medusa Fig. 23-7

27. 23.3 What Are the Major Animal Phyla? • Cnidarians have stinging cells called cnidocytes(刺细胞) that are used to capture prey and for defense • Cnidocytes contain a finely coiled filament that is explosively expelled when the trigger is touched • Some filaments inject poison into the prey • Others either stick to or entangle small prey • The venom of some can cause extreme pain or death in humans

28. Cnidarian Weaponry: The Cnidocyte trigger filament trigger nuclei (b) Cnidocytes Fig. 23-8

29. 23.3 What Are the Major Animal Phyla? • Cnidarians have a gastrovascular cavity(消化循环腔), a sac-like digestive chamber with a single opening that serves as both a mouth and an anus • Tentacles force the prey through the opening into the gastrovascular cavity • Digestive enzymes secreted into this cavity break down some of the food, and further digestion occurs within the cells lining the cavity • Undigested wastes are expelled from the opening when digestion is completed

30. 23.3 What Are the Major Animal Phyla? • Many corals secrete hard skeletons • In many coral species, polyps form colonies • Colonial polyps secrete a hard external skeleton of calcium carbonate • The skeleton remains after the polyp dies • New polyps build on the skeletal remnants of earlier generations • Coral reefs are found in both cold and warm oceans, and provide undersea habitats that support a wealth of diversity

31. 23.3 What Are the Major Animal Phyla? • Comb jellies belong to the phylum Ctenophora(栉水母动物门) • These animals resemble some cnidarians, but form, instead, a distinct evolutionary lineage • The comb jellies use cilia to move • All comb jellies are carnivorous, eating tiny invertebrate animals that they capture with sticky tentacles • Most comb jellies are hermaphroditic(雌雄同体) and can release both eggs and sperm into seawater; fertilized eggs gradually develop into larvae and then adults

32. 23.3 What Are the Major Animal Phyla? • Flatworms may be parasitic or free living • Flatworms are bilaterally symmetrical and belong to the phylum Platyhelminthes(扁形动物门) • Many species are parasites(寄生动物), organisms that live in or on the body of another organism • Non-parasitic, free-living flatworms inhabit aquatic, marine, and moist terrestrial habitats • Flatworms can reproduce both sexually and asexually; most are hermaphroditic(雌雄同体), having both male and female sexual organs

33. 23.3 What Are the Major Animal Phyla? • Flatworms have organs but lack respiratory and circulatory systems • They possess a distinct head, along with sensory organs • The eyespots(眼点) of freshwater planarians(涡虫) detect light and dark • Their nervous system consist of clusters of nerve cells called ganglia(神经节) (singular: ganglion) in the head, forming a simple brain • They have paired nerve cords (神经索)that extend the length of the body and conduct nerve signals to and from the ganglia

34. 23.3 What Are the Major Animal Phyla? • Flatworms have organs but lack respiratory and circulatory systems (continued) • In the absence of a respiratory system, gas exchange is accomplished by diffusion between body cells and the environment • In the absence of a circulatory system, the digestive cavity has a branching structure that reaches all parts of the body and allows digested nutrients to diffuse into nearby cells

35. 23.3 What Are the Major Animal Phyla? • Flatworms are bilaterally symmetrical, rather than radially symmetrical • This body plan is accompanied by cephalization, where sense organs are concentrated in the anterior portion of the body • This enhances an animal’s ability to respond appropriately to any stimuli that it encounters

36. 23.3 What Are the Major Animal Phyla? • Some flatworms are harmful to humans • Tapeworms(绦虫) can infect people who eat improperly cooked beef, pork, or fish that has been infected by the worms • Tapeworm larvae form encapsulated resting structures, called cysts(包囊), in the muscles of these animals • The cysts hatch in the human digestive tract, and the young tapeworms attach themselves to the lining of the intestine

37. The Life Cycle of the Human Pork Tapeworm A human eats poorly cooked pork with live cysts 1 A larval tapeworm is liberated by digestion and attaches to the human’s intestine 2 adult tapeworm head (attachment site) 6 inches The tapeworm matures in a human intestine, producing a series of reproductive segments; each segment contains both male and female sex organs 3 The larvae form cysts in pig muscle 8 Eggs are shed from the posterior end of the worm and are passed with human feces 4 A pig eats food contaminated by infected feces 5 Larvae hatch in the pig’s intestine 6 The larvae migrate through blood vessels to pig muscle 7 Fig. 23-10

38. Flatworm Diversity Fig. 23-9

39. 23.3 What Are the Major Animal Phyla? • Annelids are segmented worms and belong to the phylum Annelida(环节动物门) • The annelid body is divided into a series of repeating units (segmentation) • The segments contain identical copies of nerves, excretory structures (排泄器官), and muscles that allows for complex movement • Annelids have a fluid-filled coelom • The coelom functions as a hydrostatic skeleton(流体静力学性骨骼), where pressurized fluid provides a framework against which muscles can act

40. 23.3 What Are the Major Animal Phyla? • Many annelids reproduce sexually • Some species are hermaphroditic; others have separate sexes • During copulation, sperm are transferred from one individual to the other • In hermaphroditic species, sperm transfer may be mutual, with each partner donating and receiving sperm • Some annelids reproduce asexually by fragmentation • The body breaks into two pieces, each of which regenerates the missing part

41. 23.3 What Are the Major Animal Phyla? • Annelids have a closed circulatory system (blood is confined to the heart and blood vessels) • The circulatory system distributes gases and nutrients throughout body • The blood is filtered and wastes are removed by excretory organs callednephridia(肾管)

42. 23.3 What Are the Major Animal Phyla? • The annelid nervous system consists of: • A simple brain in the head • A series of repeating paired segmental ganglia joined by a pair of ventral nerve cords extending the length of the body

43. 23.3 What Are the Major Animal Phyla? • The annelid digestive system consists of a tubular gut with two openings—a mouth and an anus • Digestion occurs in a series of compartments • Pharynx(咽): draws in food • Esophagus(食道): conducts food to crop • Crop(嗉囊): stores food • Gizzard(砂囊): grinds food • Intestine(肠): absorbs digested nutrients

44. An Annelid, The Earthworm nephridia coelom excretory pore intestine ventral nerve cord anus coelom brain pharynx mouth ventral vessel hearts esophagus crop gizzard intestine Fig. 23-11 ventral nerve cord

45. 23.3 What Are the Major Animal Phyla? • The 9,000 species of annelids fall into three main subgroups • Oligochaetes(寡毛纲) • Polychaetes (多毛纲) • Leeches(蛭纲)

46. 23.3 What Are the Major Animal Phyla? • Oligochaetes (寡毛纲) • These worms live in moist terrestrial habitats • This group includes earthworms and its relatives • As a result of their extensive tunneling through soils, earthworms have major roles in aerating the soil and mixing its organic matter, which are favorable activities for plant growth

47. 23.3 What Are the Major Animal Phyla? • Polychaetes (多毛纲) • Most polychaetes live in the ocean • Some have tubes from which they project feathery gills used for gas exchange and to filter the water for microscopic food • Others have segmental, paired, fleshy paddles that are used for locomotion

48. 23.3 What Are the Major Animal Phyla? • Leeches (蛭纲) • Leeches live in fresh water or moist terrestrial habitats • They are either carnivorous (prey on smaller invertebrates) or parasitic (suck the blood of larger animals)

49. Diverse Annelids Fig. 23-12

50. 23.3 What Are the Major Animal Phyla? • Most mollusks have shells • The phylum Mollusca(软体动物门) consists of clams, snails, and cephalopods • Most mollusks have open circulatory systems(开管式循环系统) (blood is not confined to the heart and blood vessels) • Blood percolates through a hemocoel(血腔) (or blood cavity), bathing the internal organs directly • Mollusks have an extension of the body wall, called a mantle(外套膜), that forms a chamber for the gills and, in shelled species, secretes the shell