systematic adaptations of phylum platyhelminthes n.
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Systematic Adaptations of Phylum Platyhelminthes. The Flatworms. Derived Characteristics. Organ level of organization Well developed, specialized anatomical structures Incomplete gastrulation Gastrovascular cavity with one opening Triploblastic

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derived characteristics
Derived Characteristics
  • Organ level of organization
    • Well developed, specialized anatomical structures
  • Incomplete gastrulation
    • Gastrovascular cavity with one opening
  • Triploblastic
    • True mesodermal tissue filling space between endoderm and ectoderm (note “parenchyma”)
  • Bilateral Symmetry
    • 2 symmetrical sides about longitudinal axis
  • Cephalization
    • Concentration of sensory apparatus at anterior end
body form development
Body Form & Development
  • Acoelomate
  • Parenchyma derived from mesodermal tissue
  • Elongated body
  • No appendages
  • Simple integument
  • Ciliated in free living flatworms, but lacking cilia in parasitic forms
  • Glandular tissue associated with skin
    • Mucous glands
    • “Dual gland” for adhesion and release
skeletal muscular
Skeletal & Muscular
  • Hydrostatic Skeleton
  • Parenchymal tissue holds a constant (“static”) volume of water (“hydro”)
  • Compression/contraction in one direction must necessarily result in expansion/elongation in a different direction
  • Well developed muscles are present in the body wall
    • Longitudinal
    • Circular
    • Oblique
muscular arrangement
Muscular arrangement
  • Predict the result from the contraction of:
    • Longitudinal muscle (2)
    • Circular muscle (1)
    • Oblique muscle (3)
watch these flatworms move
Watch these flatworms move
nervous sensory
Nervous & Sensory
  • Centralized nervous system
    • Paired solid, ventral nerve cords
    • “Ladder” type nervouse organization – Transverse nerves connecting longitudinal nerve cords
  • Concentration of nerve tissue forming cephalic ganglia (simple brain)
nervous sensory1
Nervous & Sensory
  • Cephalization
    • Concentration of sense organs in anterior body region
  • Sense organs
    • Photoreceptors (note “ocelli”)
    • Chemoreceptors (note “auricles”)
  • The development of the digestive cavity is incomplete, forming a gastrovascular cavity with a single opening
  • Digestion is largely extracellular, although some flatworms complete the process in food vacuoles (intracellular)
  • The class turbellaria are free living and carnivorous, and have well developed gastrovascular cavities
  • The other classes of flatworms are parasitic, dependent upon the host for digestion
  • Mouth located ventrally
  • Free living turbellaria have an extensible pharynx
  • The highly branched gastrovascular cavity brings digested food in close proximity to all body tissues
  • As the gastrovascular cavity has only 1 opening, wastes are excreted through the pharynx or retained
watch these flatworms feeding
Watch these flatworms feeding
  • The gastrovascular cavity in parasitic forms is diminished (as in this photo) or absent (as in the tapeworms)
  • When present, the gastrovascular cavity is generally Y shaped
osmoregulation vs excretion
Osmoregulation vs. Excretion?
  • Osmoregulation is the removal of excess water
  • Excretion is the removal of metabolic waste (mostly nitrogen compounds like ammonia or urea that accumulate from metabolism of protein) and excess dissolved materials (salts)
  • The flame cells are concerned with osmoregulation
  • Metabolic wastes are generally removed by simple diffusion
excretion osmoregulation
Excretion & Osmoregulation
  • “Protonephridia” – primitive excretory tubules driven by Flame Cells.
  • The “flame” consists of several flagellae that drive fluids through tubules that lead to collecting tubules
excretion osmoregulation1
Excretion & Osmoregulation
  • There is considerable variation in the structure of osmoregulation systems in the flatworm classes, from simple excretory pores to a bladder
  • Due to the simplicity of the flatworm body form, many are capable of reproducing asexually. In low density populations, asexual reproduction (by budding or fission) may be predominant
  • Flatworms are monoecious (one reproductive form – AKA hermaphroditic) but generally are unable to self-fertilize
  • Parasitic forms have complex life cycles, often involving one or more intermediate hosts.
flatworm reproductive organs
Flatworm reproductive organs
  • This flatworm is free living. Its muscular and digestive systems, while not shown above, are well developed
  • Note the presence of both male and female gonads (Monoecious)
fluke reproductive organs
Fluke reproductive organs
  • This liver fluke is parasitic. It depend on its host for locomotion and digestion, allowing it to devote more of its energy and anatomy to reproduction
  • Note that is also is monoecious. The testes are more pink, and located posteriorly
  • The ovary is darker and more centrally located
tapeworm reproductive organs
Tapeworm reproductive organs
  • Tapeworms are parasitic. Their digestive system is absent. Almost their entire anatomy is devoted to reproduction
  • They have a segmented body, with both testes and ovaries located in each segment
trematode life cycle
Trematode Life Cycle
classes of platyhelminthes
Classes of Platyhelminthes
  • The Phylum platyhelminthes is divided into 4 classes
    • Class Turbellaria – The free living flatworms
    • Class Trematoda – The digenetic flukes
      • Digenetic = 2 or more hosts
    • Class Monogenea – The monogenetic flukes
      • Monogenetic = 1 host
    • Class Cestoda – The tapeworms
class turbellaria
Class Turbellaria
  • The only class of free living flatworms
  • Ciliated epidermis with mucous secreting rhabdites
  • Acoelomate
  • Extensible pharynx
  • Includes the planaria
class trematoda
Class Trematoda
  • Parasitic flukes
  • Syncytial tegument (multinucleate skin) without cilia
  • Y shaped gastrovascular cavity
  • Oral sucker for obtaining food and ventral sucker for attachment
  • No hooks for attachment to host
  • Digenetic – 2 or more hosts
    • Intermediate host – usually an invertebrate, frequently a mollusc
    • Definitive host – a vertebrate
  • Includes fasciola, schistosoma and clonorchis
class monogenea
Class Monogenea
  • Parasitic flukes
  • Syncytial tegument (multinucleate skin) without cilia
  • Free living, ciliated larvae
  • Y shaped gastrovascular cavity
  • A single oral sucker
  • A series of posterior hooks (opisthaptor) for attachment to the host
  • Monogenetic – parasitic on a single host, usually a fish, amphibian or reptile
class cestoda
Class Cestoda
  • Tapeworms, parasitic to the digestive tracts of vertebrates
  • Syncytial tegument without cilia
  • The tegument is covered with fingerlike extensions to increase the surface area for food absorption
  • Gastrovascular cavity is absent
  • Anterior structure (scolex) with hooks/suckers for attachment to the host
  • Body is formed into segments called proglottids. Each proglottid has testes and ovaries. Self-fertilization is possible
  • Gravid proglottids from feces of infected animals may be consumed by a new host, or may be spread by consuming larvae in the flesh of an infected animal