Worms: Flatworms, Roundworms, and Rotifers Objectives: State the distinguishing characteristics of flatworms Describe the anatomy of a planarian Compare and contrast free-living and parasitic flatworms Diagram the life cycle of a fluke Describe the life cycle of a tapeworm Describe the body plan of a pseudocoelomate Explain the relationship between humans and three types of parasitic roundworms Describe the anatomy of a rotifer

Platyhelminthes Members of the phylum Platyhelminthes are called flatworms. Their bodies develop from three germ layers and are more complex than those of sponges, cnidarians, and ctenophores. Flatworms have Bilateral symmetry, with dorsal and ventral surfaces, right and left sides, and anterior and posterior ends.

What Is a Flatworm? Flatworms are soft, flattened worms that have tissues and internal organ systems. They are the simplest animals to have three embryonic germ layers, bilateral symmetry, and cephalization.

What Is a Flatworm? Flatworms are acoelomates, which means they have no coelom. A coelom is a fluid-filled body cavity that is lined with tissue derived from mesoderm. The digestive cavity is the only body cavity in a flatworm. Flatworms have bilateral symmetry.

What Is a Flatworm? Three germ layers of a flatworm Flatworms are the simplest animals to have three embryonic germ layers—ectoderm, endoderm, and mesoderm.

Form and Function in Flatworms Flatworms are thin and most of their cells are close to the external environment. All flatworms rely on diffusion for respiration, excretion, and circulation.

Form and Function in Flatworms Free-living flatworms have organ systems for digestion, excretion, response, and reproduction. Parasitic species are typically simpler in structure than free-living flatworms.

Form and Function in Flatworms Feeding  Flatworms have a digestive cavity with a single opening through which both food and wastes pass. Near the mouth is a muscular tube called a pharynx. Flatworms extend the pharynx out of the mouth. The pharynx then pumps food into the digestive cavity.

Form and Function in Flatworms Most parasitic worms do not need a complex digestive system. They obtain nutrients from foods that have already been digested by their host.

Form and Function in Flatworms Respiration, Circulation, and Excretion  Flatworms do not need a circulatory system to transport materials.  Flatworms rely on diffusion to transport oxygen and nutrients to their internal tissues, and to remove carbon dioxide and other wastes from their bodies.

Form and Function in Flatworms Flatworms have no gills or respiratory organs, heart, blood vessels, or blood. Some flatworms have flame cells which are specialized cells that remove excess water from the body. Flame cells may filter and remove metabolic wastes.

Form and Function in Flatworms Response   In free-living flatworms, a head encloses ganglia, or groups of nerve cells, that control the nervous system. Two long nerve cords run from the ganglia along both sides of the body.

Form and Function in Flatworms Many free-living flatworms have eyespots. Eyespots are groups of cells that can detect changes in light. Most flatworms have specialized cells that detect external stimuli. The nervous systems of free-living flatworms allow them to gather information from their environment.

Form and Function in Flatworms Digestive Structures of a Planarian All flatworms, including this planarian, have organ systems that perform essential life functions. The digestive cavity is branched throughout the body and opens to the outside through the pharynx. Photo Credit: ©Carolina Biological Supply Company/Phototake

Excretory, Nervous, and Reproductive Structures of a Planarian Ganglia Nerve cords Excretory system Ovary Testes All flatworms, including this planarian, have organ systems that perform essential life functions. The excretory system (in purple) consists of many flame cells (in red) that maintain water balance and may remove waste. The nervous system (in dark gray) consists of ganglia and two nerve cords that run the length of the body. The reproductive system (in green) has testes and ovaries, or male and female reproductive organs, along both sides of the body. Flame cell Excretory tubule

Form and Function in Flatworms Movement   Free-living flatworms move in two ways. Cilia on their epidermal cells help them glide through the water and over the bottom of a stream or pond. Muscle cells controlled by the nervous system allow them to twist and turn.

Form and Function in Flatworms Reproduction  Most free-living flatworms are hermaphrodites that reproduce sexually. A hermaphrodite is an individual that has both male and female reproductive organs. Two worms join in a pair and deliver sperm to each other. The eggs are laid in clusters and hatch within a few weeks.

Form and Function in Flatworms Asexual reproduction takes place by fission, in which an organism splits in two. Each half grows new parts to become a complete organism. Parasitic flatworms often have complex life cycles that involve both sexual and asexual reproduction.

Classes of Flatworms What are the characteristics of the three Classes of flatworms?

Classes of Flatworms The three main groups of flatworms are turbellarians Trematoda- flukes Cestoda- tapeworms Most turbellarians are free-living. Most other flatworm species are parasites.

Classes of Flatworms Class Turbellarians Turbellarians are free-living flatworms. Most live in marine or fresh water. Most species live in the sand or mud under stones and shells.

Classes of Flatworms Class Trematoda- Flukes Flukes are parasitic flatworms. Most flukes infect the internal organs of their host. Usually don’t kill the host. Host are typically Animals and humans No special sense organs Mostly aquatic Most less than 1cm long Schistosoma- Genus of flukes that cause Schistosomiasis.

Form and Function in Flatworms Flukes can infect the blood or organs of the host. Some flukes are external parasites. In the typical life cycle of parasitic flukes, the fluke lives in multiple hosts.

Form and Function in Flatworms Life Cycle of a Blood Fluke Flukes usually infect the internal organs of their host. The life cycle of the blood fluke Schistosoma mansoni involves two hosts: humans and snails.

Form and Function in Flatworms A blood fluke’s primary host is a human. Blood flukes infect humans by burrowing through the skin. Human intestine Tailed larva Flukes usually infect the internal organs of their host. The life cycle of the blood fluke Schistosoma mansoni involves two hosts: humans and snails.

Form and Function in Flatworms Once inside the human, they are carried to the blood vessels of the intestines. In the intestines the flukes mature and reproduce. Embryos are released and are passed out of the body with feces. Adult fluke Embryo Flukes usually infect the internal organs of their host. The life cycle of the blood fluke Schistosoma mansoni involves two hosts: humans and snails.

Form and Function in Flatworms If the embryos reach water, they develop into swimming larvae that infect a snail (the intermediate host). An intermediate host is an organism in which a parasite reproduces asexually. Embryo Ciliated larva Flukes usually infect the internal organs of their host. The life cycle of the blood fluke Schistosoma mansoni involves two hosts: humans and snails. Life Cycle of a Blood Fluke

Form and Function in Flatworms Larvae that result from asexual reproduction are released from the snail into the water to begin the cycle again. Flukes usually infect the internal organs of their host. The life cycle of the blood fluke Schistosoma mansoni involves two hosts: humans and snails. Life Cycle of a Blood Fluke

Form and Function in Flatworms Class Cestoda- Tapeworms  Tapeworms are long, flat, parasitic worms that are adapted to life inside the intestines of their hosts. No organs for locomotion, senses, or digestion. They absorb from the hosts digestive system. Can be up to 40 feet long.

Form and Function in Flatworms Tapeworms have no digestive tract and absorb digested food directly through their body walls. The head of an adult tapeworm, called a scolex, is a structure that can contain suckers or hooks. The tapeworm uses its scolex to attach to the intestinal wall of its host.

Form and Function in Flatworms Structures of a Tapeworm Tapeworms are parasitic flatworms that live in the intestines of their host. A tapeworm attaches to the host using hooks or suckers on its scolex. A single tapeworm is made of many proglottids. The youngest proglottids are at the anterior (head) end, and the largest and most mature proglottids are at the posterior (tail) end. After eggs have been fertilized, proglottids break off and release zygotes that are then passed out of the host in feces.

Form and Function in Flatworms Proglottids are the segments that make up most of the worm's body. Mature proglottids contain both male and female reproductive organs. Sperm produced by the testes (male reproductive organs), can fertilize eggs of other tapeworms or of the same individual.

Form and Function in Flatworms After the eggs are fertilized, the proglottids break off and burst to release the zygotes. The zygotes are passed out of the host in feces. The eggs ingested by an intermediate host hatch and grow into larvae. Larvae burrow into the intermediate host’s muscle tissue.

Form and Function in Flatworms Larvae form a dormant protective stage called a cyst. If a human eats incompletely cooked meat containing these cysts, the larvae become active and grow into adult worms within the human’s intestines, beginning the cycle again.

Nematoda and Rotifera Members of the Phyla Nematoda and Rotifera have bilateral symmetry and contain a fluid-filled space. This space holds the internal organs and serves as a storage area for eggs and sperm. It also supports the body and provides a structure against which the muscles can contract.

Phylum Nematoda Nematoda is made up of roundworms, worms with long slender bodies that taper at both ends. Roundworms are Pseudocoelomates Pseudocoelomates is a hollow fluid filled cavity that has mesoderm lining the outside and endoderm on the inside. (coelomates have mesoderm lining the entire cavity)

What Is a Roundworm? Roundworms are un-segmented worms that have pseudocoeloms and digestive systems with two openings—a mouth and an anus.

What Is a Roundworm? This cavity is partially lined with tissue derived from the mesoderm and is called a pseudocoelom, meaning, “false coelom.” Roundworms such as hookworms are unsegmented worms that have a pseudocoelom and a digestive system with a mouth and an anus. Roundworms develop from three germ layers, and a pseudocoelom forms between the endoderm and mesoderm layers.

What Is a Roundworm? Roundworms have a digestive tract with two openings. Food moves in one direction through the digestive tract of roundworms. Any food that is not digested leaves the body through the anus.

Form and Function in Roundworms Roundworms have specialized tissues and organ systems that carry out essential physiological functions.

Form and Function in Roundworms Feeding Many free-living roundworms use grasping mouthparts and spines to catch and eat other small animals.

Form and Function in Roundworms Respiration, Circulation, and Excretion Roundworms exchange gases and excrete metabolic waste through their body walls. They depend on diffusion to carry nutrients and waste through their bodies.

Form and Function in Roundworms Response Roundworms have simple nervous systems, consisting of several ganglia. Several nerves extend from ganglia in the head and run the length of the body. These nerves transmit sensory information and control movement.

Form and Function in Roundworms Movement Fluid in the pseudocoelom and muscles extending the length of their bodies function as a hydrostatic skeleton. Aquatic roundworms contract muscles to move like snakes through the water. Soil-dwelling roundworms push their way through the soil by thrashing around.

Form and Function in Roundworms Reproduction  Roundworms reproduce sexually. Most species have separate sexes. Roundworms reproduce using internal fertilization. Parasitic roundworms often have life cycles that involve two or three different hosts or several organs within a single host.

Roundworms and Human Disease What roundworms cause human disease?

Roundworms and Human Disease Parasitic roundworms include trichinosis-causing worms, filarial worms, ascarid worms, and hookworms.

Roundworms and Human Disease Trichinosis-Causing Worms  Adult Trichinella worms live and mate in the intestines of their hosts. Female worms carrying fertilized eggs burrow into the intestinal wall and release larvae. Larvae travel through the bloodstream and burrow into organs and tissues.

Roundworms and Human Disease The larvae form cysts and become inactive in the host’s muscle tissue. Trichinella completes its life cycle only when another animal eats muscle tissue containing these cysts. Humans can get trichinosis by eating raw or incompletely cooked pork.

Roundworms and Human Disease Filarial Worms  Filarial worms are threadlike worms that live in the blood and lymph vessels of birds and mammals. They are transmitted by biting insects. Large numbers of filarial worms may block the passage of fluids within lymph vessels and cause swelling.

Roundworms and Human Disease Ascarid Worms  Ascaris lumbricoides is a serious parasite of humans and many other vertebrate animals. It absorbs digested food from the host’s small intestine. Ascaris lumbricoides is commonly spread by eating foods that are not washed properly.

Roundworms and Human Disease Ascaris Life Cycle 1 Human ingests food or water containing Ascaris eggs. Ascaris lumbricoides fill the host’s intestine. These worms absorb the host’s digested food and can cause severe malnutrition. Blockage of the intestine can be severe enough that it causes death.

Roundworms and Human Disease Ascaris Life Cycle 2 The eggs travel to the small intestine and develop into larvae. Ascaris lumbricoides fill the host’s intestine. These worms absorb the host’s digested food and can cause severe malnutrition. Blockage of the intestine can be severe enough that it causes death.

Roundworms and Human Disease Ascaris Life Cycle 3 Larvae enter blood vessels and are carried to the lungs

Roundworms and Human Disease Ascaris Life Cycle 4 Larvae are coughed up and swallowed. They then travel to the small intestine where they develop to maturity Ascaris lumbricoides fill the host’s intestine. These worms absorb the host’s digested food and can cause severe malnutrition. Blockage of the intestine can be severe enough that it causes death.

Roundworms and Human Disease Ascaris Life Cycle 5 Eggs are released and leave the host in faces. Ascaris lumbricoides fill the host’s intestine. These worms absorb the host’s digested food and can cause severe malnutrition. Blockage of the intestine can be severe enough that it causes death.

Roundworms and Human Disease Hookworms  Hookworm eggs hatch and develop in the soil. They use sharp tooth like plates and hooks to burrow into the skin and enter the bloodstream.

Roundworms and Human Disease Hookworms travel through the blood of their host to the lungs and down to the intestines. There, they suck the host’s blood, causing weakness and poor growth.

Phylum Rotifera Most Rotifers are transparent, free-living animals that live in fresh water. When they are in dry conditions the look like grains of sand and then will go back to their normal state when wet. Have cilia near the mouth. Looks like a pair of rotating wheels. They sweep food- algae, bacteria, and protozoans- into their digestive tracks.

Rotifers

Copyright Pearson Prentice Hall  Annelids Objectives: What are the defining features of annelids What are the characteristics of the three classes of annelids Test Friday Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall What Is an Annelid? What are the defining features of annelids? Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall What Is an Annelid? What Is an Annelid? Annelids are worms with segmented bodies. They have a true coelom that is lined with tissue derived from mesoderm. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall What Is an Annelid? Three Germ Layers of an Annelid Has a true Coelom- Eucoelomate Annelids are among the simplest animals to have a true coelom that is lined with mesoderm. Annelids are also called segmented worms because the body is divided into many similar segments. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall What Is an Annelid? The body of an annelid is divided into segments. Each segment is separated by septum, which are internal walls between each segment. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall What Is an Annelid? Body segments may carry eyes, antennae, other sense organs, or be specialized for functions such as respiration. Bristles called setae may be attached to each segment. Annelids have a tube-within-a-tube digestive tract that food passes through from the mouth to the anus. Copyright Pearson Prentice Hall

Form and Function in Annelids Annelids have complex organ systems. Many of these systems are unique because of the segmented body plan of this group. Copyright Pearson Prentice Hall

Form and Function in Annelids Feeding and Digestion In carnivorous species, the pharynx usually holds two or more sharp jaws that are used to attack prey. Annelids that feed on decaying vegetation have a pharynx covered with sticky mucus. Other annelids obtain nutrients by filter feeding. Copyright Pearson Prentice Hall

Form and Function in Annelids In earthworms, the pharynx pumps food and soil into the esophagus. The food then moves through the crop, where it can be stored. It then moves through the gizzard, where it is ground into smaller pieces. The food is absorbed farther along in the digestive tract in the intestine. Copyright Pearson Prentice Hall

Form and Function in Annelids Circulation  Annelids typically have a closed circulatory system, in which blood is contained within a network of blood vessels. Copyright Pearson Prentice Hall

Form and Function in Annelids Blood in the dorsal (top) vessel moves toward the head of the worm. The dorsal blood vessel functions like a heart because it contracts rhythmically and helps pump blood. Dorsal blood vessel Copyright Pearson Prentice Hall

Form and Function in Annelids Blood in the ventral (bottom) vessel runs from head to tail. Ventral blood vessel Copyright Pearson Prentice Hall

Form and Function in Annelids In each body segment, a pair of smaller blood vessels connect the dorsal and ventral blood vessels and supply blood to the internal organs. Copyright Pearson Prentice Hall

Form and Function in Annelids Respiration  Aquatic annelids often breathe through gills. A gill is an organ specialized for the exchange of gases underwater. Land-dwelling annelids take in oxygen and give off carbon dioxide through their moist skin. Copyright Pearson Prentice Hall

Form and Function in Annelids Excretion   Digestive waste passes out through the anus. Cellular waste containing nitrogen is eliminated by nephridia. Copyright Pearson Prentice Hall

Form and Function in Annelids Nephridia are excretory organs that filter fluid in the coelom. Nephridia Copyright Pearson Prentice Hall

Form and Function in Annelids Response   Most annelids have a well-developed nervous system consisting of a brain and several nerve cords. Brain Ganglia Copyright Pearson Prentice Hall

Form and Function in Annelids Movement   Annelids have two groups of body muscles that function as part of a hydrostatic skeleton. Longitudinal muscles run from the front of the worm to the rear and can contract to make the worm shorter and fatter. Copyright Pearson Prentice Hall

Form and Function in Annelids Circular muscles wrap around each body segment and can contract to make the worm longer and thinner. The earthworm moves by alternately contracting these two sets of muscles. Copyright Pearson Prentice Hall

Form and Function in Annelids Reproduction    Most annelids reproduce sexually. Some species use external fertilization and have separate sexes. Other annelids are hermaphrodites. Two worms attach to each other, exchange sperm, and then store the sperm in special sacs. Copyright Pearson Prentice Hall

Form and Function in Annelids When eggs are ready for fertilization, a clitellum secretes a mucus ring into which eggs and sperm are released. A clitellum is a band of thickened, specialized segments. After eggs are fertilized in the ring, the ring slips off the worm's body and forms a protective cocoon. Young worms hatch weeks later. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Groups of Annelids What are the characteristics of the three classes of annelids? Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Groups of Annelids Annelids are divided into three classes oligochaetes leeches polychaetes Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Groups of Annelids Oligochaetes Oligochaetes contains earthworms and their relatives. Oligochaetes typically have streamlined bodies and relatively few setae compared to polychaetes. Most oligochaetes live in soil or fresh water. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Groups of Annelids Leeches The class Hirudinea contains the leeches. Leeches are typically external parasites that suck the blood and body fluids of their host. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Groups of Annelids Leeches have powerful suckers at both ends of their bodies that help them cling to their hosts. Some leeches force a muscular extension called a proboscis into the tissue of their host. Others slice into the skin with a razor-sharp pair of jaws. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Groups of Annelids The leech uses its pharynx to suck blood from the wound. Some leeches release a substance that anesthetizes the wound—keeping the host from knowing it has been bitten. Leeches were once used to treat medical conditions. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Groups of Annelids Polychaetes Polychaetes include sandworms, bloodworms, and their relatives. Polychaetes are marine annelids that have paired, paddlelike appendages tipped with setae. The setae are brushlike structures on the worm. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Ecology of Annelids Ecology of Annelids Earthworms and many other annelids spend their lives burrowing through soil, aerating and mixing it. Earthworms help plant matter decompose. Earthworm castings are rich in nitrogen, phosphorus, potassium, micronutrients, and beneficial bacteria. Copyright Pearson Prentice Hall