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Chapter 26: Sponges, Cnidarians, and Unsegmented Worms Section 1: Introduction to the Animal Kingdom Introduction to the Animal Kingdom 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 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 membraneenclosed organelles An animal is a multicellular eukaryotic heterotroph whose cells lack cell walls 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 Trends in Animal Evolution Small clusters of nerve cells are called ganglia In the most complex animals, large numbers of nerve cells gather together to form larger structures called brains Chapter 26: Sponges, Cnidarians, and Unsegmented Worms Section 2: Sponges 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 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 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 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 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 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 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 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 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 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 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 Chapter 26: Sponges, Cnidarians, and Unsegmented Worms Section 3: Cnidarians 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 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 flowerlike polyp and the motile bell-shaped medusa Some cnidarians, such as sea nettles and sea anemones, are solitary. Others, such as gorgonian coral polyps, are colonial. 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 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 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 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 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 Form and Function in Cnidarians Most cnidarians can reproduce both sexually and asexually Polyps can produce new polyps asexually by budding When medusae mature, they reproduce sexually by releasing gametes into the water Fertilization occurs either in open water or inside an egg-carrying medusa The zygote grows into a ciliated larva that swims around for some time Later, the larva settles down, attaches to a hard surface, and changes into a polyp that begins the cycle again Hydras and Their Relatives Class Hydrozoa is made up of cnidarians that spend most of their lives as polyps, although they usually have a short medusa stage Most hydrozoan polyps grow in branching sessile colonies Range in length from a few centimeters to more than a meter Specialized polyps perform particular functions Feeding Reproduction Defense Hydras and Their Relatives Most common are the hydras Hydras can reproduce either asexually by budding or sexually by producing eggs and sperm in their body walls In most species of hydras, the sexes are separate However, a few species are hermaphrodites An individual that has both male and female reproductive organs and produces both sperm and eggs Hydras and Their Relatives One unusual hydrozoan in the Portuguese man-of-war Form floating colonies that contain several polyps One polyp forms a balloon-like float that keeps the colony on the surface Some of the polyps produce long stinging tentacles that paralyze and capture prey Some polyps digest the food held by tentacles Jellyfish Class Scyphozoa Go through the same life-cycle stages as hydrozoans Some jellyfish, such as the lion’s mane, often grow up to 2 meters in diameter The largest jellyfish ever found was more than 3.6 meters in diameter and had tentacles more than 30 meters long The nematocysts of most jellyfish are harmless to humans, but a few can cause painful stings One tiny Australian jellyfish has a toxin powerful enough to cause death in 3 – to 20 minutes Sea Anemones and Corals Class Anthozoa Most beautiful and ecologically important invertebrates Have only the polyp stage in their life cycle Adult polyps reproduce sexually by producing eggs and sperm that are released into the water The zygote grows into a ciliated larva that settles to the ocean bottom and becomes a new polyp Many anthozoans also reproduce asexually by budding Sea Anemones and Corals Sea anemones are solitary polyps that live in the sea from the low-tide line to great depths Although they can catch food with the nematocysts on their tentacles, many shallowwater species depend heavily on their photosynthetic symbionts Some sea anemones can grow up to a meter in diameter Sea Anemones and Corals Corals grow in shallow tropical water around the world Corals produce skeletons of calcium carbonate or limestone Most corals are colonial As a coral colony grows, new polyps are produced by budding Sea Anemones and Corals Coral colonies grow very slowly, but they may live for hundreds, or even thousands, of years Together, countless coral colonies produce huge structures called coral reefs Some of these reefs are enormous and contain more rock and living tissue than even the largest human cities The Great Barrier Reef off the coast of Australia is more than 2000 km long and some 80 km wide How Cnidarians Fit into the World Certain fish, shrimp, and other small animals live among the tentacles of large sea anemones Corals and the reefs provide shelter for thousands of species of marine life Reefs protect the land from erosion Jewelry and decorations Medical research Chapter 26: Sponges, Cnidarians, and Unsegmented Worms Section 4: Unsegmented Worms Unsegmented Worms Unsegmented worms have bodies that are not divided into special segments Phylum Platyhelminthes Consists of simple animals called flatworms Phylum Nematoda Consists of long, thin worms called roundworms Flatworms The members of the phylum Platyhelminthes are the simplest animals with bilateral symmetry Most members of this phylum exhibit enough cephalization, or development of the anterior end, to have what we call a head Many flatworms are no more than a few millimeters thick, although they may be up to 20 meters long Flatworms have more developed organ systems than either sponges or cnidarians Form and Function in Flatworms Flatworms feed in either of two very different ways Worms may be carnivores that feed on tiny aquatic animals Free-living flatworms have a gastrovascular cavity with one opening at the end of a muscular tube called a pharynx They use the pharynx to suck food into the gastrovascular cavity The gastrovascular cavity forms an intestine with many branches along the entire length of the worm Form and Function in Flatworms In the intestines, enzymes help break down the food into small particles These particles are taken inside the cells of the intestinal wall, where digestion is completed Like Cnidarians, flatworms expel undigested material through the mouth Form and Function in Flatworms Many other flatworms are parasites that feed on blood, tissue fluids, or pieces of cells inside the body of their host In many parasitic flatworms, the digestive tract is simpler than in free-living forms Tapeworms, which live within the intestines of their host, do not have any digestive tract at all They have hooks and/or suckers with which they latch onto the intestinal wall of the host Form and Function in Flatworms From this position, they can simply absorb the food that passes by – food that has already been broken down by the host’s digestive enzymes Flatworms lack any kind of specialized circulatory or respiratory system Freshwater flatworms such as planarians have structures called flame cells that help them get rid of extra water Form and Function in Flatworms Free-living flatworms have nervous systems that are much more developed than those of cnidarians and sponges They have a definite head in which a simple brain is located One or more long nerve cords run from the brain down the length of the body on either side Many flatworms have one or more pairs of light-sensitive organs called ocelli, or eyespots Form and Function in Flatworms The nervous system of free-living flatworms allows them to gather information from their environment – information that they use to locate food and to find dark hiding places Parasitic flatworms often do not have much of a nervous system Form and Function in Flatworms Free-living flatworms usually use two means of locomotion at once Cilia on their epidermal cells help them glide through the water Muscle cells controlled by the nervous system allow them to twist and turn so that they are able to react to environmental conditions Form and Function in Flatworms Reproduction in free-living flatworms can be either sexual or asexual Most free-living flatworms are hermaphrodites The eggs hatch within a few weeks Planarians The free-living flatworms belong to the class Turbellaria Most familiar members of this class are planarians Turbellarians vary greatly in color, form, and size Although most Turbellarians are less that 1 cm in length, some giant land planarians, which are found in moist tropical areas, can attain lengths of more than 60 cm Flukes Class Trematoda contains parasitic flatworms known as flukes Most flukes are internal parasites that infect the blood and organs These flukes have complicated life cycles that involve at least two different host animals Blood flukes are found primarily in Southeast Asia, North Africa, and other tropical areas Humans are the primary hosts of blood flukes Flukes Most flukes are hermaphrodites and undergo sexual reproduction in a manner similar to that of free-living flatworms Flukes produce many more eggs than free-living flatworms Blood flukes lay so many eggs that the tiny blood vessels of the host’s intestine break open The broken blood vessels leak both blood and eggs into the intestine Flukes The eggs are not digested by the host and thus become part of the feces In developed countries, where there are toilets and proper sewage systems, these eggs are usually destroyed in the sewage treatment process But in many undeveloped parts of the world, human wastes are simply tossed into streams or even used as fertilizer Flukes Once the fluke eggs get into the water, they hatch into swimming larvae When these larvae find a snail of the correct species, they burrow inside it and digest its tissues The snail is an intermediate host for the fluke In the intermediate host, the flukes reproduce asexually Flukes The resulting new worms break out of the snail and swim around in the water If they find a human, the worms bore through the skin and eat their way to the blood vessels In the blood, the get carried around through the heart and lungs to the intestine, where they live as adults Flukes People infected with blood flukes get terribly sick They become weak and often die – either as a direct result of the fluke infection or because they cannot recover from other diseases in their weakened condition Tapeworms Members of the class Cestoda are long, flat parasitic worms that live a very simple life They have a head called a scolex on which there are several suckers and a ring of hooks These structures attach to the intestinal walls of humans and other animals Adult human tapeworms can be up to 18 meters long Tapeworms almost never kill their host Tapeworms Behind the scolex of the tapeworm is a narrow neck region that is constantly dividing to form many proglottids, or sections, that make up most of the body of the tapeworm The youngest and smallest proglottids are at the anterior end of the tapeworm Male and female reproductive organs are contained in the proglottids Tapeworms If food or water contaminated with tapeworm eggs is consumed by cows, pigs, fish, or other intermediate hosts, the eggs enter the intermediate host and hatch into larvae These larvae grow for a time and then burrow into the muscle tissue of the intermediate host and form a dormant protective stage called a cyst Tapeworms If a human eats raw or incompletely cooked meat containing these cysts, the larvae become active within the human host Once inside the intestine of a new host, they latch onto the intestinal wall and grow into adult worms Roundworms Members of the phylum Nematoda, which are known as roundworms, are among the simplest animals to have a digestive system with two openings – a mouth and an anus Food enters through the mouth, and undigested food leaves through the anus Roundworms may be the most numerous of all multicellular animals A single rotting apple can contain as many as 90,000 roundworms Form and Function in Roundworms Most roundworms are free-living All roundworms have a long tube-shaped digestive tract with openings at both ends Any material in the food that cannot be digested leaves through an opening called the anus Roundworms breathe and excrete their metabolic wastes through their body walls They have no internal transport system Form and Function in Roundworms Roundworms have simple nervous systems They have several ganglia in the head region but no definite brain Roundworms reproduce sexually Fertilization takes place inside the body of the female How Unsegmented Worms Fit into the World Do not have a lot of positive influence on humans Responsible for some of the most painful and horrific diseases known Hookworm Eye worm Trichinosis