Chapter 26: Sponges, Cnidarians, and Unsegmented Worms

1. Chapter 26: Sponges, Cnidarians, and Unsegmented Worms Section 1: Introduction to the Animal Kingdom

2. Introduction to the Animal Kingdom • The animal kingdom is the most diverse in form • Each animal performs the essential functions of life in its own special way • Two divisions that we will use to separate the animal kingdom are vertebrates and invertebrates • Vertebrates have a backbone • Invertebrates have no backbone

3. What Is an Animal? • All animals share certain basic characteristics • Animals are heterotrophs (they do NOT make their own food) • Instead, they obtain the nutrients and energy they need by feeding on organic compounds that have been made by other organisms

4. What Is an Animal? • Animals are multicellular, which means that their bodies are composed of more than one cell • Animal cells are also eukaryotic – they contain a nucleus and membrane-enclosed organelles • An animal is a multicellular eukaryotic heterotroph whose cells lack cell walls

5. Cell Specialization and Division of Labor • The bodies of animals contain many types of specialized cells • Each specialized cell has a shape, physical structure, and chemical composition that make it uniquely suited to perform a particular function within a multicellular organism • For this reason, groups of specialized cells carry out different tasks for the organism – division of labor

6. What Animals Must Do to Survive • In order to survive, animals must be able to perform a number of essential functions • For each animal group we study in the next several chapters, we will examine these functions and describe the cells, tissues, organs, and organ systems that perform them

7. Feeding • Animals have evolved a variety of ways to feed • Herbivores eat plants • Carnivores eat animals • Parasites live and feed either inside or attached to outer surfaces of other organisms, causing harm to the host • Filter feeders strain tiny floating plants and animals from the water around them • Detritus feeders feed on tiny bits of decaying plants and animals

8. Respiration • Living cells consume oxygen and give off carbon dioxide in the process of cellular respiration • Entire animals must respire, or breathe, in order to take in and give off these gases • Small animals that live in water or in moist soil may respire through their skin

9. Respiration • For large active animals, however, respiration through the skin is not efficient • The respiratory systems these animals have evolved take many different forms in adaptations suited to different habitats

10. Internal Transport • Some aquatic animals can function without an internal transport system • But once an animal reaches a certain size, it must somehow carry oxygen, nutrients, and waste products to and from cells deep within its body • Many multicellular animals have evolved a circulatory system in which a pumping organ called a heart forces a fluid called blood through a series of blood vessels

11. Excretion • Cellular metabolism produces chemical wastes such as ammonia that are harmful and must be eliminated • Small aquatic animals depend on diffusion to carry wastes from their tissues into the surrounding water • But larger animals, both in water and on land, must work to remove poisonous metabolic wastes

12. Response • Animals must keep watch on their surroundings to find food, spot predators, and identify others of their own kind • To do this, animals use specialized cells called nerve cells, which hook up together to form a nervous system

13. Response • Sense organs, such as eyes and ears, gather information from the environment by responding to light, sound, temperature, and other stimuli • The brain, which is the nervous system’s control center, processes the information and regulates how the animal responds • The complexity of the nervous system varies greatly in animals

14. Movement • Some animals are sessile, which means that they live their entire adult lives attached to one spot • But many animals are motile, which means that they move around • To move, most animals use tissues called muscles that generate force by contracting • In the most successful groups of animals, muscles work together with a skeleton, or the system of solid support in the body

15. Movement • Insects and their relatives wear their skeletons on the outside of their bodies • exoskeletons • Reptiles, birds, and mammals have their skeletons inside their bodies • endoskeletons • We call the combination of an animal’s muscles and skeleton its musculo – skeletal system

16. Reproduction • Animals must reproduce or their species will not survive • Some animals switch back and forth between asexual and sexual reproduction • Many animals that reproduce sexually bear their young alive

17. Reproduction • Others lay eggs • The eggs of some species hatch into baby animals that look just like miniature adults • These baby animals increase in size but do not change their overall form • Direct development

18. Reproduction • In other species, eggs hatch into larvae, which are immature stages that look and act nothing like the adults • As larvae grow, they undergo a process called metamorphosis in which they change shape dramatically • Indirect development

19. Trends in Animal Evolution • The levels of organization become higher as animals become more complex in form • The essential functions of less complex animals are carried out on the cell or tissue level of organization • As you move on to more complex animals, you will observe a steady increase in the number of specialized tissues • You will also see those tissues joining together to form more and more specialized organs and organ systems

20. Trends in Animal Evolution • Some of the simplest animals have radial symmetry; most complex animals have bilateral symmetry • Some of the simplest animals have body parts that repeat around an imaginary line drawn through the center of their body • Radial symmetry • Animals with radial symmetry never have any kind of real “head” • Many of them are sessile, although some drift or move in a random pattern

21. Trends in Animal Evolution • Most complex invertebrates and all vertebrates have body parts that repeat on either side of an imaginary line drawn down the middle of their body • One side of the body is a mirror image of the other • These animals are said to have bilateral symmetry

22. Trends in Animal Evolution • Animals with bilateral symmetry have specialized front and back ends as well as upper and lower sides • Anterior = front end • Posterior = back end • Dorsal = upper side • Ventral = lower side

23. Trends in Animal Evolution • More complex animals tend to have a concentration of sense organs and nerve cells in their anterior (head) end • This gathering of sense organs and nerve cells into the head region is called cephalization • Nerve cells in the head gather into clusters that process the information gathered by the nervous system and control responses to stimuli

24. Trends in Animal Evolution • Small clusters of nerve cells are calledganglia • In the most complex animals, large numbers of nerve cells gather together to form larger structures called brains

25. Chapter 26: Sponges, Cnidarians, and Unsegmented Worms Section 2: Sponges

26. Sponges • Sponges are among the most ancient of all animals that are alive today • Most sponges live in the sea, although a few live in freshwater lakes and streams • Sponges inhabit almost all areas of the sea – from the polar regions to the tropics and from the low-tide line down into water several hundred meters deep

29. Sponges • Sponges belong to the phylum Porifera • Literally means pore-bearers • Tiny openings all over their body • Sponges were once thought to be plants • Sponges are sessile and show little detectable movement • Sponges are heterotrophic, have no cell walls, and contain several specialized cell types that live together

30. Sponges • Sponges are very different from other animals • Sponges have nothing that even vaguely resembles a mouth or gut, and they have no specialized tissues or organ systems • Most biologists believe that sponges evolved from single-celled ancestors separately from other multicellular animals • The evolutionary line that gave rise to sponges was a dead end that produced no other groups of animals

31. Form and Function in Sponges • Very simple body plan • The body of a sponge forms a wall around a central cavity • In this wall are thousands of pores • A steady current of water moves through these pores into the central cavity • This current is powered by the flagella of cells called collar cells

32. Form and Function in Sponges • The water that gathers in the central cavity exits through a large hole called the osculum • The current of water that flows through the body of a sponge delivers food and oxygen to the cells and carries away cellular waste products • The water also transports gametes or larvae out of the sponge’s body

33. Form and Function in Sponges • Many sponges manufacture thin, spiny spicules that form the skeleton of the sponge • A special kind of cell called an amebocyte builds the spicules from either calcium carbonate or silica • These spicules interlock to form beautiful and delicate skeletons • The softer but stronger sponge skeletons that we know as natural bath sponges consist of fibers of a protein called spongin

35. Form and Function in Sponges • Sponges are filter feeders that sift microscopic particles of food from the water that passes through them • All digestion in sponges is intracellular; it takes place inside cells • The water flowing through a sponge simultaneously serves as its respiratory, excretory, and internal transport system • As water passes through the body wall, sponge cells remove oxygen from it and give off carbon dioxide to it

36. Form and Function in Sponges • The water that flows through the body of a sponge also plays a role in sexual reproduction • Although eggs are kept inside the body wall of a sponge, sperm are released into the water flowing through the sponge and are thus carried out into the open water • If those sperm are taken in by another sponge, they are picked up by amebocytes and carried to that sponge’s eggs, where fertilization occurs

37. Form and Function in Sponges • The zygote that results develops into a larva that swims and can be carried by currents for a long distance before it settles down and grows into a new sponge • Sponges can also reproduce asexually • Faced with cold winters, some freshwater sponges produce structures called gemmules • Sphere-shaped collections of amebocytes surrounded by a tough layer of spicules • Can survive long periods of freezing temperatures and drought • When conditions become favorable, gemmules grow into new sponges

38. Form and Function in Sponges • Sponges can also reproduce asexually by budding • In this process, part of a sponge simply falls off the parent and grows into a new sponge • Remarkable powers of regeneration

39. How Sponges Fit into the World • Sponges provide housing for many other marine animals • Sponges are also involved in symbiotic relationships with other organisms • Humans have used the dried and cleaned bodies of some sponges in bathing • Some chemicals that sponges secrete are being used as powerful antibiotics that are used to treat bacteria and fungi

41. Chapter 26: Sponges, Cnidarians, and Unsegmented Worms Section 3: Cnidarians

42. Cnidarians • The phylum Cnidaria includes many animals with brilliant colors and unusual shapes • Jellyfish, sea anemones, etc. • These beautiful and fascinating animals are found all over the world, but most species live only in the sea

43. What is a Cnidarian? • Cnidarians are soft-bodied animals with stinging tentacles arranged in circles around their mouth • Some cnidarians live as single individuals • Others live as groups of dozens or even thousands of individuals connected into a colony • All cnidarians exhibit radial symmetry and have specialized cells and tissues • Many cnidarians have life cycles that include two different-looking stages, the sessile flowerlikepolyp and the motile bell-shaped medusa

44. Some cnidarians, such as sea nettles and sea anemones, are solitary. Others, such as gorgonian coral polyps, are colonial.

45. What is a Cnidarian? • Both polyps and medusa have a body wall that surrounds an internal space called the gastrovascular cavity • This is where digestion takes place • The body wall consists of three layers: • Epidermis • Layer of cells that covers the outer surface of the cnidarian’s body • Mesoglea • Located between the epidermis and the gastroderm • Gastroderm • Layer of cells that covers the inner surface, lining the gastrovascular cavity

47. Form and Function in Cnidarians • Almost all cnidarians capture and eat small animals by using stinging structures called nematocysts, which are located on their tentacles • Poison-filled sac containing a tightly coiled spring loaded dart • When an animal touches a nematocyst, the dart uncoils and buries itself into the skin of the animal • Paralyzes or kills the prey

48. Form and Function in Cnidarians • From here, the cnidarian’s tentacles push the food through the mouth and into the gastrovascular cavity • There the food is gradually broken up into tiny pieces • These food fragments are taken up by special cells in the gastroderm that digests them further • The nutrients are then transported throughout the body by diffusion • Any materials that cannot be digested are passed back out through the mouth, which is the only opening in the gastrovascular cavity

49. Form and Function in Cnidarians • Because most cnidarians are only a few cell layers thick, they have not had to evolve many complicated body systems in order to survive • There is no organized internal transport network or excretory system in cnidarians • Cnidarians also lack a central nervous system and anything that could be called a brain • They have simple nervous systems called nerve nets • Concentrated around the mouth

50. Form and Function in Cnidarians • Cnidarians lack muscle cells that most other animals use to move about • Many of the epidermal cells in cnidarians can change shape when stimulated by the nervous system • Cnidarian polyps can expand, shrink, and move their tentacles by relaxing or contracting these epidermal cells