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Body Wall of Cnidarians


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Body Wall of Cnidarians

  2. 2. Body WallIn a cnidarianpolyp, such as hydra, thebody wall surroundingthe gastrovascular cavityconsists of an outerepidermis (ectordermal)and an innergastrodermis(endodermal) withmesoglea between them.
  3. 3. Mesoglea Mesoglea lies between the epidermis and the gastrodermis and adheres to both layers. It is gelatinous, or jelly like, and has no fibers or cellular elements in hydrozoan polyps. It is thicker in medusae and has elastic fibers; in scyphozoan medusae, it has ameboid cells and epitheliomuscular cells.
  4. 4. Gastrodermis The gastrodermis, a layer of cells lining the gastrovascular cavity, consists of large, ciliated, columnar epithelial cells with irregular flat bases. Cells of the gastrodermis include nutritive- muscular, interstitial, and gland cells and, in classes other than Hydrozoa, cnidocytes also included. Gonads are gastrodermal in most cnidarians.
  5. 5.  Nutritive muscular cells are usually tall columnar cells that have laterally extended bases containing myofibrils. Water is brought into the cavity through the mouth by the beating of the cilia on the nutritive-muscular cells in hydrozoans or by ciliated cells in the pharynx of anthozoans and serves as a hydrostatic skeleton. Interstitial cells scattered among the bases of the nutritive cells can transform into other cell types. Gland cells are tall cells that secrete digestive enzymes.
  6. 6.  Epitheliomuscular cellsForm most of the epidermis and serve both for covering and for muscular contraction.The bases of most of these cells are extended parallel to the tentacle or body axis and contain myofibrils, contractions of these fibrils shorten the tentacles or body. Interstitial cellsUndifferentiated stem cells found among the bases of the epitheliomuscular cells. Differentiation of interstitial cells produce cnidoblasts, sex cells, buds, nerve cells, and others, but generally not epitheliomuscular cells (which reproduce themselves).
  7. 7.  Gland cellsAbundant around the mouth and in the pedal disc of hydra.Secrete mucus or adhesive material. Nerve cellsOften multipolar, although in more highly organized cnidarians, the cells may be bipolar.Their processes (axons) form synapses with sensory cells and other nerve cells, and junctions with epitheliomuscular cells and cnidocytes.Both one-way and two-way synapses with other nerve cells are present.
  8. 8.  CnidocytesOccur throughout the epidermis.They may be between the epitheliomuscular cells or housed in invaginations of these cells.Most abundant on the tentacles. Sensory cellsScattered among the other epidermal cells, especially around the tentacles and mouth.The free end of each sensory cell bear a flagellum, which is the sensory receptor for chemical and tactile stimuli.
  9. 9. CNIDAE Secreted within cells called cnidoblasts Abundant on the feeding tentacles of all species and within the digestive cavity of some species Cnidal morphology is crucial in making species identification Functions of cnidae: -food collection -defense -locomotion
  10. 10. CNIDAE 3 major types -Nematocysts occur in all cnidarian classes can be stinging or tangling depending on type of cnidarian -Spirocysts only found in Anthazoa contribute to the adhesive stickiness of the tentacles -Ptychocysts only occur in the anthazoan order Ceriantharia used for building protective tubes
  11. 11. CNIDAE OFCNIDARIA-Nematocysts( Blue )-Spirocysts( Yellow )
  12. 12. Nematocysts Discharged Can only be discharged once Both mechanical and chemical stimuli may act to trigger firing – triggered by cnidocil The discharged is initiated by the opening of capsule operculum Then, the tubules will begin to evert out with a twisting motion The discharge may involve the increase of osmotic pressure within the capsule or because of release of tension within capsule wall
  13. 13. NERVE NET Simple nervous system In the centre of nerve net is the nerve ring which controls swimming and where to go The nerve cells help to coordinate the work of other body cells that are linked in the net- if touched, whole body will react Nerve net consist of sensory neuron and motor neuron which are connected by the intermediate neuron The communication of nerve cells are via chemical synapses