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. 14.10 Phylum Platyhelminthes General Characteristics Bilateral symmetry: body can be divided along one plane of symmetry to yield 2 mirrored halves (anterior, posterior, dorsal, ventral, left and right) Has 1 digestive cavity Acoelomates: lack a coelom (body cavity) Exhibit cephalization: has a head region with sensory structures Body Cavity Classification General Characteristics Triploblastic: contain 3 well defined germ layers ◦ Has mesoderm: region between endo- and ectoderm made of parenchyma ◦ Mesoderm enables the formation of some internal organs (muscular, excretory, and reproductive) ◦ Mesoderm also gives rise to the Parenchyma- a form of solid tissue containing cells and fibers General Characteristics Reach the organ system level of organization Has a central nervous system Platyhelminthes “Firsts” Bilateral symmetry Has digestive cavity Triploblastic Reach the organ system level of organization Cephalization Central nervous system First with an excretory system How are Platyhelminthes different from cnidarians? Cnidarians Platyhelminthes Mesoglea Mesoderm No organ systems Organ systems Diploblastic Triploblastic GVC Digestive cavity Radial Symmetry Bilateral Symmetry Not cephalized Cephalized Nerve net Nervous system with brain Cnidocytes No cnidocytes Gonads Complex reproductive system General Structure: Epidermis Most general characteristics are describing Turbellaria class Epidermis: made from the ectoderm ◦ Ciliated: especially on the ventral surface to aid in movement ◦ Contain many gland cells that secrete a mucous covering to help move General Structure: Epidermis Epidermis has rhabdites: rod-like structures in the cells of the epidermis that are discharged and form a protective mucous covering by expanding when released General Structure: inside the epidermis Contains layers of muscle cells (fibers) ◦ Run circularly, longitudinally, and diagonally ◦ Come from the mesoderm Parenchyma cells: ◦ Develop from the mesoderm ◦ Fills the space between the muscle cells and the visceral organs ◦ Layer that prevents them from being coelomates Locomotion Movement is a concerted effort of ciliary action, mucous, and muscular movements Most movement accomplished by Turbellaria …. Why? The head (superior) is raised while the other portion (inferior) is kept against the surface Glides slowly Anterior end bends from side to side Nutrition and Digestion Class Cestoda are the exception to the following notes on nutrition and digestion ◦ Cestodes have no digestive tract because they are parasites that depend on their host for nutrients- they absorb nutrient from their host Nutrition and Digestion Other classes have: Mouth: near the middle of the ventral surface; opens to the pharynx Pharynx: tubular muscular organ ◦ Contains many gland cells ◦ Can be extended from the mouth during the feeding process ◦ Secrete enzymes to help soften prey ◦ Sucking action from the pharynx breaks off small pieces of the prey Class Turbellaria Ingesting Food Pharynx Nutrition and Digestion Intestine ◦ Tri-clad Intestine (3 trunks)= class Turbellaria ◦ Bi-clad (2 Trunks)= Class Trematoda ◦ No digestive tract= Cestoda) Excretion and Osmoregulation Platyhelminthes are the first organism with an excretory system Consists of Protonephridium: first kidney ◦ System lies in the parenchyma and consists of a network of tubules that run the length of the worm on each side and opens to the surface by minute pores ◦ Side branches terminate in tiny enlargements called flame bulb: cup shaped terminal end that contains flagella to propel the fluid throughout the network to the exit pores (nephridiopores) Excretion and Osmoregulation Primary function of the flame bulb system is to remove the excess water from the tissues Circulatory and Respiratory System Platyhelminthes contain no circulatory or respiratory system Respiration occurs through epidermal cells of the whole body surface (diffusion) To allow enough oxygen to pass in and carbon dioxide to pass out through diffusion-> the thickness can’t be too great This is the reason why the organism is so FLAT!!!! Nervous System Consists of the simplest nervous system called the sub-epidermal nerve plexus Resembles the nerve net of the cnidarians Functions to send the nerve impulses from one end to the other ◦ Consists of a brain, nerve cords, and side branches Nervous System Brain: a mass of ganglion cells at the anterior end ◦ Centered anteriorly ◦ Not needed for muscular coordination involved in locomotion ◦ Functions to initiate behavior and receives stimuli from sensory organs and sends it to the rest of the body Nerve cord: run from the brain to the posterior Side branches: come off the nerve cord and directed toward the inside of the body Forms a ladder type of system Sense Organs Ocelli: light sensitive eye spots Statocysts Have tactile and chemoreceptive cells over entire body Have organs called auricles (ear-like lobes on the side of their head) ◦ Functions in finding food (chemoreceptive) ◦ If they are cut off they have a hard time finding food Reproduction and Regeneration Most information about class Turbellaria Can reproduce asexually and sexually Asexual reproduction accomplished by fission ◦ The area behind the pharynx constricts and the organism separate into 2 animals ◦ Each part will regenerate missing parts Regeneration 29 Many species have remarkable powers of regeneration and repair wounds Phylum Platyhelminthes Reproduction and Regeneration Sexual reproduction ◦ Almost all flatworms are hermaphroditic: contain both male and female sex organs in every organism ◦ Have discrete testes and ovaries ◦ Have a system of tubes and chambers in which fertilization occur ◦ Do not practice self-fertilization-> they reproduce by cross-fertilization ◦ After breeding season the organs degenerate and regenerates new at the beginning of the next season Protandry Mutualistic insemination Sperm is produced first and the organisms exchange sperm with another The organism holds the sperm until the eggs are ready Eggs develop later Platyhelminthes Classification Class Turbellaria ◦ Free living planarians & marine flatworms Class Trematoda ◦ Internal Flukes Class Cestoda ◦ Tapeworms Classification Platyhelminthes Trematoda Planaria Aspidobothrea Digenea Monogenea Cestoda Class Turbellaria Most free living flatworms Marine or freshwater Class of the planaria Can regenerate Not parasitic Planaria class are carnivorous- feeding on small crustaceans, nematodes, rotifers, and insects Most have chemoreceptors to trap prey in mucous (rhabdites) The notes previously taken were on class Turbellaria Form Fits Function The idea that the structure of an organism/part of an organism is related to its function Examples: ◦ Location of the mouth on the Platyhelminthes ◦ Lack of a digestive tract in the Cestoda Class ◦ Shape/depth of the planaria ◦ Turbellaria is the only class highly motile Pretty planaria, not all flatworms are ugly parasites Types and Adaptations of Parasites Endoparasites: Parasites that live inside their host Exoparasites: Parasites that live outside their host Adaptations to a parasitic lifestyle: ◦ Small size- to be undetected ◦ High reproductive capacity ◦ Takes only what they need from the host- not all kill their host ◦ Protective/stabilizing features for attachment ◦ Contains only necessary organ/features ◦ Forms protective cysts for when its outside a host ◦ Penetration glands ◦ Structures (hooks and suckers) for attachment Class Trematoda Class of the parasitic fluke Endoparasites Leaf-like in structure No->little external cilia (does not want to move) Oral and Ventral suckers (attachment) Poorly developed sense organs Biclad digestive tract Require 2 or more hosts Muscular pharynx to permit worm to pump food into gut Sub-Class Digenea Parasitizes all types of vertebrates in a wide range of sites Most cycles include: ◦ Intermediate host: site of asexual reproduction to increase in number of individuals (Mollusc) ◦ Definitive host: site of sexual reproduction where eggs are released (vertebrate) ◦ Some have a Secondary intermediate host Examples are: ◦ Clonorchis sinensis- Liver Fluke ◦ Schistosoma- Blood Fluke ◦ Paragonimus- Lung Fluke Generalize Fluke Body Plan Types of Transmission Passive Transmission: transmission into the host that requires no action from the parasite ◦ Ingestion Active Transmission: transmission into the host that requires the parasite to “actively” work to gain entry into the host ◦ Burrowing Example #1 Clonorchis sinensisLiver Fluke Infects humans, dogs, cats, pigs Found in China, Japan, SE Asia Life Cycle: ◦ Definitive Host: adult parasite found in the bile duct of humans and other fish eating mammals ◦ Intermediate Host: Primary: Snail Secondary: Fish ◦ Mode of Infection: Passive transmission by eating raw/poorly cooked infected fish ◦ Causes: abdominal pain, cirrhosis of the liver, blockage of the bile duct, death Trematode Lifecycle Vocabulary Definitive Host: site of sexual reproduction Miracidium: free swimming ciliated larvae Intermediate Host: site of asexual repro. Sporocyst: produced inside Intermediate host; reproduce asexually to make more sporocysts or redia Redia: 2nd asexual phase to produce redia or cercaria Cercaria: free swimming larval form that emerges from the snail; contains motile tail to swim to next host Metacercarial Cyst: juvenile flukes that burrow into muscle of (secondary) host Fluke Life Cycle Every: Egg Mirror: Miracidium (in water) Spotted: Sporocyst (in snail- primary intermediate host) Red: Redia (in snail- primary intermediate host) Certainly: Cercaria (in snail and water) Met: Metacercaria (in 2nd intermediate host) Approval: Adult (definitive host) Fluke Life Cycle Fluke Life Cycle Clonorchis sinensis- Liver Fluke Example #2: Schistosoma Affects 200 million people in Africa, S. America, Middle East, and Far East Not hermaphroditic: have separate male and female species Dimorphic: the male and female body are structurally different ◦ Male: is larger(width) and contains a gynecophoric canal (groove in the body of the male to contain the female ◦ Female: longer and more slender; “snuggles” in the male canal Species of Schistosoma S. mansoni: adult found in the veins of the large intestine and feeds on blood S. japonicum: found in veins of small intestine; most severe S. haematobium: found in veins of urinary bladder Side Effects of Schistosoma Eggs in the intestinal wall can cause ulceration, abscesses, bloody diarrhea, and pain Eggs can travel to the liver or other sites and cause problems at those sites and can impede circulation If liver is affected it can cause cirrhosis Blood Flukes: Schistosoma japonicum & Schistosoma mansoni Schistosoma Life Cycle Schistosomiasis ◦ Deadly prominent disease in many regions of the world ◦ Bores into the skin of the definitive host and travels in the circulatory system to the heart the lungs and the kidneys where it feeds and grows ◦ Inflammation is caused by eggs becoming trapped in the hosts tissues 62 Chinese liver fluke ◦ Lives in the bile duct of humans, cats, and dogs (1-2 cm.) ◦ Goes through two intermediate hosts ◦ Infection occurs from ingestion of raw fish Phylum Platyhelminthes Life Cycle of Schistosoma Swimmer’s Itch Encysted metacercaria of avian schistosomes Example #3: Paragonimus Lung Flukes Parasitizes wild carnivores, humans, pigs, rodents Humans(vertebrates) are the definitive host Snail is the primary intermediate host Crab is the secondary intermediate host Humans get infected by passive transmission > eating raw crab Upon eating the metacercaria encysts itself in the intestine then penetrates the lung and diaphragm can cause chronic bronchitis Human Lung Fluke Life Cycle Class Cestoda Class of the tapeworms Have long, flat bodies No digestive system…Why??? No cilia in adults Contain microtriches: covering surface of their body serves to increase surface area providing greater absorption Hermaphroditic Well developed muscles No sense organs Class Cestoda Has a scolex: organ for attachment (hooks and/or suckers) Most are polyzoic: body is divided up into a series of proglottids Proglottid: individual segment of a tapeworm body; contains their own set of reproductive organs (can be 3-4,000/animal) Strobila: the length of the tapeworm body behind the scolex consisting of a chain of proglottids Tapeworm Anatomy Growth of a Tapeworm Germinative zone: located behind the scolex; location where new proglottids are formed ◦ As the younger proglottids differentiate each moves posteriorly in the strobila (because of the creation of new proglottid) and its gonads mature ◦ The proglottids can be fertilized by another proglottid in the same or different strobila ◦ Mature eggs can be released through an opening in the proglottid or leave the host when the proglottids are separated from the main body of the worm General information on the lifecycle of tapeworms 2 Hosts ◦ Definitive host: carnivore ◦ Intermediate host: herbivore Adults live in the intestine of the definitive host Larval stages (cysticercus) encyst in muscle of intermediate host Causes : weight loss, indigestion, diarrhea, intestinal blockage, pain Examples of Class Cestoda Taenia saginata: Beef tapeworm ◦ Humans get infected by eating raw/undercooked beef Taenia solium: Pork tapeworm ◦ Humans get infected by eating raw/undercooked pork Diphyllobothrium latum: Fish tapeworm ◦ Humans get infected by eating raw/undercooked fish ◦ Largest tapeworms in humans; common in Great Lakes Echinococcus granulosus: Dog tapeworm ◦ More later Taenia saginata Life Cycle - Human/Beef Tapeworm Pork Tapeworm Taenia solium – Human/Pork Tapeworm Pork Tapeworm More dangerous than beef tapeworm because the larva can encyst in the definitive host rather than intermediate host (by accident) ◦ Causes the formation of bladder worms called cysticerci in human host outside of intestine ◦ Causes a condition called cysticercosis: formation of cysticerci in several organs (eyes and brain)-> leads to blindness, neurological problems, and death ◦ May also form hydatid cyst (more later) Hydatid Cysts in Human Brain Fish Tapeworm Dog Tapeworm Definitive host: Dog Intermediate host: humans, sheep, cattle, deer Humans get infected because dogs can carry tapeworms on their tongues Causes the formation of a special kind of cysticercus called a hydatid cyst: has a single large chamber with daughter cysts inside each containing thousands of scolices Each scolex will produce a worm when eaten by a dog (dog would need to eat human to continue cycle-> usually dead end for parasite) Hydatid cysts can grow slowly and reach the size of a basketball if not detected Hydatid cyst in human heart Comparison of Digestive System Class Feeding TURBELLARIANS FEED ON SMALL INVERTEBRATES Digestion Mouth is used for both ingestion & excretion. Mouth leads to pharynx and is followed by the gut Cestodes FEED ON HOST (INTESTINE OF A VERTEBRATE ANIMAL) Possess no gut or simple gut No mouth or digestive tract Absorb food from environment Digestion is intracellular Trematodes FEED ON HOST TISSUE THROUGH PHARYNX. Contain mouth and simple gut Digestion is extracellular and then intracellular
