Platyhelminthes Characteristics

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  Annelida, Chordata, Echinoderm and Platyhelminthes (Animal Phylum)

  • (Author)
  • 2014(Publication Date)
  • Academic Studio

    (Publisher)

  ________________________ WORLD TECHNOLOGIES ________________________ Chapter- 16 Flatworm Platyhelminth worms Temporal range: 40–0 Ma Bedford's flatworm, Pseudobiceros bedfordi Scientific classification Kingdom: Animalia (unranked): Protostomia (unranked): Spiralia (unranked): Platyzoa Phylum: Platyhelminthes Gegenbaur, 1859 Classes Cestoda Monogenea Trematoda Turbellaria The flatworms , known in scientific literature as Platyhelminthes or Plathelminthes (from the Gree k πλατύ, platy , meaning flat and ἕ λμινς (root: ἑ λμινθ -), helminth-, meaning worm) are a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrate animals. Unlike other bilaterians, they have no body cavity, and no ________________________ WORLD TECHNOLOGIES ________________________ specialized circulatory and respiratory organs, which restricts them to flattened shapes that allow oxygen and nutrients to pass through their bodies by diffusion. In traditional zoology texts Platyhelminthes are divided into Turbellaria, which are mostly non-parasitic animals such as planarians, and three entirely parasitic groups: Cestoda, Trematoda and Monogenea. Turbellarians are mostly predators, and live in water or in shaded, humid terrestrial environments such as leaf litter. Cestodes (tapeworms) and trematodes (flukes) have complex life-cycles, with mature stages that live as parasites in the digestive systems of fish or land vertebrates, and intermediate stages that infest secondary hosts. The eggs of trematodes are excreted from their main hosts, whereas adult cestodes generate vast numbers of hermaphroditic, segment-like proglottids which detach when mature, are excreted and then release eggs. Unlike the other parasitic groups, the monogeneans are external parasites infesting aquatic animals, and their larvae metamorphose into the adult form after attaching to a suitable host.

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  The Invertebrate Tree of Life

  • Gonzalo Giribet, Gregory D. Edgecombe(Authors)
  • 2020(Publication Date)
  • Princeton University Press

    (Publisher)

  43

  PLATYHELMINTHES

  Platyhelminthes20 (the “flatworms”) constitutes a cosmopolitan phylum of aquatic and terrestrial invertebrates known from about 29,300 (Zhang, 2011; based on estimates from S. Tyler) to 30,000 described species (Caira and Littlewood, 2013). These include both free-living and parasitic worms, three-quarters of the diversity belonging to a clade of mostly vertebrate parasitic forms (flukes, tapeworms, and their relatives). Flatworms have become one of the most important models for studying regeneration (mostly on planarians or triclads but also on macrostomorphs), and the flukes and tapeworms are among the most studied parasites. An important number of species impact on human health, parasitizing 200 million people in 74 countries (Chitsulo et al., 2004), as is the case for the five species of human blood flukes in the genus Schistosoma, the agent of schistosomiasis or bilharzia. In addition, platyhelminths have played a major role in understanding animal evolution, especially given their acoelomate condition, completely ciliated epidermis, and blind digestive system with a generally ventral mouth—features that made them a candidate for the “most basal” bilaterians. It is for this reason that many books and science documentaries persist in referring to the platyhelminths as the first animals to incorporate a third embryonic layer (the mesoderm), the first excretory organs, or the first steps toward cephalization, their generally ventral mouth and blind gut supposed to signal an “intermediate” evolutionary position. They are thus often referred to as “basal bilaterians” or “basal protostomes”—see our discussion about “basal” in the introductory chapter. Paradoxically, their complex reproductive organs were cited as an oddity of parallel origins of complexity. Instead, the core of Platyhelminthes is now known to be a derived group of protostomes, deeply nested within Spiralia, yet some former members of the phylum, Acoelomorpha, still retain this key evolutionary position—as sister group to all other bilaterians—and display many of these supposedly primitive traits (see chapter 12

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  Echinoderm and Platyhelminthes (Animal Phylum)

  • (Author)
  • 2014(Publication Date)
  • White Word Publications

    (Publisher)

  ________________________ WORLD TECHNOLOGIES ________________________ Chapter- 7 Flatworm Platyhelminth worms Temporal range: 40–0 Ma Bedford's flatworm, Pseudobiceros bedfordi Scientific classification Kingdom: Animalia (unranked): Protostomia (unranked): Spiralia (unranked): Platyzoa Phylum: Platyhelminthes Gegenbaur, 1859 Classes Cestoda Monogenea Trematoda Turbellaria The flatworms , known in scientific literature as Platyhelminthes or Plathelminthes (from the Greek πλατύ, platy , meaning flat and ἕ λμινς (root: ἑ λμινθ -), helminth-, meaning worm) are a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrate animals. Unlike other bilaterians, they have no body cavity, and no ________________________ WORLD TECHNOLOGIES ________________________ specialized circulatory and respiratory organs, which restricts them to flattened shapes that allow oxygen and nutrients to pass through their bodies by diffusion. In traditional zoology texts Platyhelminthes are divided into Turbellaria, which are mostly non-parasitic animals such as planarians, and three entirely parasitic groups: Cestoda, Trematoda and Monogenea. Turbellarians are mostly predators, and live in water or in shaded, humid terrestrial environments such as leaf litter. Cestodes (tapeworms) and trematodes (flukes) have complex life-cycles, with mature stages that live as parasites in the digestive systems of fish or land vertebrates, and intermediate stages that infest secondary hosts. The eggs of trematodes are excreted from their main hosts, whereas adult cestodes generate vast numbers of hermaphroditic, segment-like proglottids which detach when mature, are excreted and then release eggs. Unlike the other parasitic groups, the monogeneans are external parasites infesting aquatic animals, and their larvae metamorphose into the adult form after attaching to a suitable host.

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  Invertebrate Zoology

  • (Author)
  • 2014(Publication Date)
  • Research World

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  Hence the Turbellaria as traditionally defined are paraphyletic. Description Traditional classifications divide the Platyhelminthes into four groups: Turbellaria and the wholly parasitic Trematoda, Monogenea and Cestoda. In this classification the Turbellaria include the Acoelomorpha (Acoela and Nemertodermatida). The name Turbellaria refers to the whirlpools of microscopic particles created close the skins of aquatic species by the movement of their cilia. Features common to all Platyhelminthes Platyhelminthes are bilaterally symmetrical animals, in other words their left and right sides are mirror images of each other; this also implies that they have distinct top and bottom surfaces and distinct head and tail ends. Like other bilaterians they have three main cell layers (it is triploblastic), while the radially symmetrical cnidarians and ctenophore have only two cell layers. Unlike most other bilaterians, platyhelminthes have no internal body cavity and are therefore described as acoelomates. They also lack specialized circulatory and respiratory organs The lack of circulatory and respiratory organs limits platyhelminths to sizes and shapes that enable oxygen to reach and carbon dioxide to leave all parts of their bodies by simple diffusion. Hence many are microscopic and the large species have flat ribbon-like or leaf-like shapes. The guts of large species have many branches, so that nutrients can diffuse to all parts of the body. Respiration through the whole surface of the body makes ________________________ WORLD TECHNOLOGIES ________________________ platyhelminthes vulnerable to fluid loss, and restricts them to environments where dehydration is unlikely: sea and freshwater; moist terrestrial environments such as leaf litter or between grains of soil; and as parasites within other animals.

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  Parasitology

  An Integrated Approach

  • Alan Gunn, Sarah J. Pitt(Authors)
  • 2022(Publication Date)
  • Wiley

    (Publisher)

  5 Platyhelminth and Acanthocephalan Parasites

  CONTENTS

  • 5.1 Introduction
  • 5.2 Phylum Platyhelminthes
  • 5.2.1 Trematoda
  • 5.3 Class Cestoda
  • 5.3.1 Order Pseudophyllidea/Diphyllobothridea
  • 5.3.2 Order Cyclophyllidea
  • 5.4 Phylum Acanthocephala

  5.1 Introduction

  In this chapter, we will introduce three of the most important groups of parasitic ‘worms’. Namely, the flatworms (flukes), the tapeworms, and the thorny headed worms. The term ‘worm’ is, in a way, unfortunate because these organisms are only very distantly related to the real worms – the Annelida. Furthermore, most Annelida are free‐living although one group, the Hirudinea, includes the leeches, some of which feed on blood and some people consider these to be parasites. The thorny‐headed worms or acanthocephalans to give them their scientific name are unusual parasites. They are common parasites, but they rarely infect humans and domestic animals and therefore seldom gain attention in the scientific literature. They do, however, have some fascinating biological traits.

  5.2 Phylum Platyhelminthes

  Members of the phylum Platyhelminthes are commonly known as the ‘flatworms’ on the not unreasonable basis that they are dorsoventrally flattened and worm‐like in appearance. They are acoelomate soft‐bodied animals that are bilaterally symmetrical (i.e., their left side is the same as their right side) with an obvious head‐end. Most platyhelminths have a mouth at the anterior end although in some free‐living species the mouth is situated at or close to the centre of the body, while in tapeworms the mouth is absent. Tapeworms also lack a gut although this is present in most other platyhelminth species and usually consists of a blind‐ending sack or series of branching tubules. The lack of an anus means that waste material is passed back through the mouth. Platyhelminths do, however, have a ramifying series of tubules that constitute their ‘excretory system’. Flame cells (protonephridia) maintain the movement of fluid within the excretory system, and the waste is removed through excretory pores. Because the excretory system removes excess water and ions, it is sometimes referred to as the osmoregulatory system. Most platyhelminths are hermaphrodites, containing both male and female reproductive organs, although in a few species there are separate male and female sexes.

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  Foundations of Wildlife Diseases

  • Richard G. Botzler, Richard N. Brown(Authors)
  • 2014(Publication Date)
  • University of California Press

    (Publisher)

  85 FOUR Flatworms trematodes and cestodes CONTENTS Introduction to Phylum Platyhelminthes 85 Trematodes (Flukes) 86 Digenetic Trematodes 86 Liver Trematodes 90 Fascioloides magna 90 Dicrocoelium dendriticum 93 Intestinal Trematodes 96 Sphaeridiotrema globulus and S. pseudoglobulus 96 Ribeiroia ondatrae 97 Blood Flukes (Schistosomes) 101 Cestodes 102 Cyclophyllidean Cestodes: Mammals 102 Life Cycles Using a Cysticercus 107 Life Cycles Using a Coenurus 108 Taenia (Multiceps) multiceps 10 8 Life Cycles Involving Hydatid Cysts 109 Echinococcus multilocularis 110 Other Echinococcus spp. 112 Cyclophyllidea: Avian Cestodes 113 Literature Cited 113 INTRODUCTION TO PHYLUM PLATYHELMINTHES Platyhelminths ( platy: f lat, helminth: worm) are a phylum of simple, soft-bodied, dorsoventrally flattened invertebrates with bilateral symmetry. While there is a blind gut in some, none have a body cavity (coelom); thus, platyhelminths are classified as acoe-lomates (Roberts and Janovy 2000). They are among the simplest animals to have a nervous system. Platyhelminths of interest for wildlife belong to the Class Cercomeridia (App. 1: Table 3). Two platyhelminth groups are of major importance in wildlife disease studies: trematodes (Subclass Trematoda), also called flukes, and cestodes (Infraclass Cestoidea), also called tapeworms (Roberts and Janovy 2000) (App. 1: Table 3). Although there are many free-living platyhelminths, all trematodes and cestodes engage in parasitic life styles. 86 flatworms TREMATODES (FLUKES) Trematodes are characterized as having an oral sucker that includes a pharynx, and with a vari-ably placed ventral sucker (acetabulum) as a hold-fast organ (Roberts and Janovy 2000) (Fig. 4.1); a few trematodes have only one sucker, usually at the anterior end (Bush et al. 2001). While lacking coeloms, trematodes have well-developed meso-derms that form the parenchyma, reproductive organs, and musculature in the adult stages (Roberts and Janovy 2000).

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  Parasitology

  • Jack Chernin(Author)
  • 2000(Publication Date)
  • CRC Press

    (Publisher)

  In bitch and puppies the larvae migrate from gut to liver, lungs and trachea. Coughed up and swallowed, they develop into L4 larvae and adults and then release eggs. ■ SUMMARY The characteristics and an outline classification of the Phylum Platyhelminthes are presented. The basic morphology and physiology of a typical cestode, trematode and nematode are described. The general plan of the life-cycles of each group is outlined. The cestodes have several different types of metacestode (larval stages) which occur within the inter-mediate hosts; and it is some of these that are the cause of severe pathology in humans and domestic animals. The trematodes have an even more complex life-cycle but the intermediate host is always a species of mollusc. The basic life-cycle and variations that occur are outlined. The nema-todes have a more regular pattern to their life-cycles. Normally the larvae moult four times into the next stage before reaching sexual maturity. END OF CHAPTER QUESTIONS PLATYHELMINTHS Question 3.1 What are the distinguishing features of the phylum Platyhelminthes? Question 3.2 How many body layers are there in platyhelminths and what are the layers called? 40 P L A T Y H E L M I N T H S Question 3.3 Question 3.4 Question 3.5 Question 3.6 Question 3.7 Question 3.8 Question 3.9 Question 3.10 CESTODES Question 3.1 Question 3.2 Question 3.3 Question 3.4 Question 3.5 Question 3.6 Question 3.7 Question 3.8 Question 3.9 Question 3.10 Question 3.11 Question 3.12 Question 3.13 Question 3.14 TREMATODES Question 3.1 Question 3.2 Question 3.3 Question 3.4 Question 3.5 Question 3.6 Question 3.7 Question 3.8 Question 3.9 Question 3.10 NEMATODES Question 3.1 Question 3.2 Question 3.3 Question 3.4 Question 3.5 What is the difference between a coelomate and an acoelomate animal? Name the different organs normally found in platyhelminths. How do these organisms ‘respire’? How do platyhelminths remove liquid metabolic waste products? Name the classes within this phylum.

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  Thorp and Covich's Freshwater Invertebrates

  Keys to Nearctic Fauna

  • James H. Thorp, D. Christopher Rogers(Authors)
  • 2015(Publication Date)
  • Academic Press

    (Publisher)

  Chapter 5

  Phylum Platyhelminthes

  Carolina Noreña     Departamento Biodiversidad y Biología Evolutiva, Museo Nacional de Ciencias Naturales (CSIC), Madrid, Spain

  Cristina Damborenea,  and Francisco Brusa     División Zoología Invertebrados, Museo de La Plata, CONICET, La Plata, Argentina

  Abstract

  The second volume in this landmark series includes an introductory chapter followed by 15 taxonomically specific chapters with identification keys to Nearctic freshwater invertebrates (protozoa through arthropods). Other than the second chapter’s treatment of the diverse, multi-phyla array of protozoa (ciliates, flagellates, and amoebas), each of the remaining 14 chapters is limited to a single phylum. Chapters include the following six sections: Introduction, Limitations (to taxonomic identification of that group), Terminology and Morphology (information needed to use the keys), Material Preparation and Preservation, Identification Keys, and References. This volume complements Volume I’s global coverage of “Ecology and General Biology,” and thus, only minimal information on those topics is included here. Volume II is devoted to the identification of inland water invertebrates of the Nearctic Bioregion including Canada, the continental United States, Mexico north of the Tropic of Cancer, Bermuda, and Greenland. Most keys terminate at either the level of genus or species, and generalized distribution data is included.

  Keywords

  Catenulida; Flatworm; Freshwater; Planaria; Rhabditophora; Turbellaria

  Chapter Outline

  Introduction  91

  Limitations  91

  Terminology and Morphology  92

  Material Preparation and Preservation  92

  Keys to Platyhelminthes  96

  Acknowledgments  109

  References  109

  Introduction

  The flatworms of the phylum Platyhelminthes comprise free-living (“Turbellaria”) and obligate parasitic organisms (Monogenea, Digenea, Aspidogastrea, and Cestoda, today grouped in Neodermata). “Turbellaria” includes an amazing variety of forms, but built in a similar way. All have the following characteristics: bilateral symmetry, organs embedded in a solid cellular matrix (the parenchyma), a sac-like gut without an anus, a nervous system with an anterior “brain” and lateral nerve chords, and internal fluids that are regulated by protonephridia. Most are cross-fertilizing hermaphrodites, with morphologically diverse structures like sclerotic parts of the male copulatory organ that forms stylets of different shape and complexity, and with endolecithal or ectolecithal eggs. Variation also can be found in the location and shape of the pharynx along the main body-axis.

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  Principles of Veterinary Parasitology

  • Dennis Jacobs, Mark Fox, Lynda Gibbons, Carlos Hermosilla(Authors)
  • 2015(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  CHAPTER 5 Platyhelminthes (‘flatworms’)

  1. 5.1 Introduction
  2. 5.2 Cestodes
     1. 5.2.1 Key concepts
  3. 5.3 Cyclophyllidean tapeworms
     1. 5.3.1 Cyclophyllidean life-cycle
     2. 5.3.2 Metacestodes
     3. 5.3.3 Taenia
        1. Metacestodes
        2. Taenia species of humans
        3. Taenia species of dogs
        4. Taenia species of cats
     4. 5.3.4 Echinococcus
        1. Metacestodes
        2. Life-cycle
        3. Hydatid disease
     5. Epidemiology
        1. Alveolar hydatid disease
     6. 5.3.5 Other cyclophyllidean tapeworms
        1. Metacestode
        2. Anoplocephala
        3. Moniezia
        4. Dipylidium
        5. Poultry cestodes
  4. 5.4 Pseudophyllidean tapeworms
     1. 5.4.1 Pseudophyllidean life-cycle
     2. Avoid common mistakes!
     3. 5.4.2 Important pseudophyllideans
  5. 5.5 Cestocidal drugs
     1. 5.5.1 Praziquantel
  6. 5.6 Trematodes
     1. 5.6.1 Digenean trematodes
        1. Body structure
        2. Life-cycles
        3. Important digenean trematodes
     2. 5.6.2 Fasciola
        1. Preparasitic life-cycle
        2. Snail biology
        3. Parasitic migration
        4. Disease manifestations
        5. Pathogenesis of acute disease
        6. Pathogenesis of chronic disease
     3. 5.6.3 Other digenean trematodes
        1. Paramphistomum
        2. Dicrocoelium
        3. Fascioloides
        4. Schistosoma
        5. Trematodes of dogs and cats
  7. 5.7 Flukicidal drugs
     1. 5.7.1 Benzimidazoles
     2. 5.7.2 Salicylanilides

  5.1 Introduction

  Platyhelminths typically have a flattened body with suckers, or similar structures, for attachment to their host. Most are hermaphrodite (i.e. each individual has male and female sex organs). The body surface (‘tegument’) is metabolically active and therefore structurally and functionally distinct from the arthropod exoskeleton, the cuticle of nematodes or mammalian skin.

  The term platyhelminth (meaning ‘flatworm’) encompasses two major parasitic groups: the Cestoda (tapeworms) and the Trematoda (flukes). Adult cestodes are segmented and ribbon-like, reminiscent of a tape-measure – hence the traditional name ‘tapeworm’ (see Figure 5.1 ). They have no alimentary tract and absorb nutrients through the tegument. In contrast, trematodes do have a mouth and internal digestive system. They are leaf-shaped and unsegmented (see Figure 5.2 ).

  Figure 5.1

  A typical tapeworm (Taenia saginata

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  Interrelationships of the Platyhelminthes

  • D T J Littlewood, R. A. Bray(Authors)
  • 2014(Publication Date)
  • CRC Press

    (Publisher)

  In contrast to other invertebrate groups-most notably molluscs, arthropods and nematodes, where there is a broad spectrum of FaRP isoforms -the complement of these neuropeptides in flatworms appears to be restricted to very few molecules. As Comparative neurobiology of Platyhelminthes 249 such, their value in flatworm phylogenetics would seem to be very limited. Conclusions In conclusion, it is clear that the phylogenetic significance of neurobiological data of flatworms is restricted. Some features may be due to parallelism, whilst others confirm postulated relationships of closely related species. However, as a conse-quence of distinct trends in the neuronal evolution, a common pattern in the organization of the nervous system and its chem-istry has been observed in all flatworms, apart from Acoela; a CNS composed of a brain and a pair of longitudinal nerve cords, and a PNS composed of minor cords and plexuses, all of which express a complement of classical and peptidic mes-senger molecules. Features possibly due to parallelism are: 1) morphological similarities superimposed on the basic orthogo-nal plan; 2) advanced features in neuronal cytoarchitecture shared by polyclads, rhabdocoels and vertebrates; 3) 'glial' cells and lamellae scattered in members of several flatworm taxa; and 4) presynaptic paramem braneous structures reminis-cent of those in arthropods and vertebrates. Nevertheless, the fundamental question posed in the introduction remains to be answered. Do these variations in the flatworm nervous systems reflect independent evolution or primitiveness? Chapter 23 The use of life-cycle characters in studies of the evolution of cestodes Jan Beveridge There has been a long history of the use of life-cycle characters in attempts to elucidate the phylogeny both of the cestodes and related groups of platyhelminth parasites.

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