Wednesday, July 29, 2020

Animal Kingdom - Notes | Class 11 | Part 2: Porifera, Cnidaria, Ctenophora

4. ANIMAL KINGDOM

PHYLUM PORIFERA (SPONGES): GENERAL CHARACTERS

  1. Grades of organization:
    • Cellular grade.
  2. Symmetry:
    • Asymmetrical. Some are radial.
  3. Coelom:
    • Acoelomate
  4. Habit and habitat:
    • Aquatic (mostly marine). Sedentary. Solitary/colonial.
  5. Digestive system:
    • Absent. Intracellular digestion.
  6. Respiratory system:
    • Absent
  7. Circulatory system:
    • Absent
  8. Reproduction:
    • Asexual (fragmentation) & Sexual.
    • Hermaphrodite (Monoecious): Male and female sex organs are seen in same individual.
    • Internal fertilization.
    • Development is indirect.
  9. Unique features:
    • Water canal (water transport) system. Millions of ostia (pores).
    • Water canal system: Here, water enters through minute pores (ostia) in the body wall into a central cavity (spongocoel), from where it goes out through osculum. Canal system is used for food gathering, gas exchange and removal of wastes.
    • Spongocoel & canals are lined with choanocytes (collar cells).
    • Body is supported by spicules and spongin fibres.
  10. Examples:
    • Sycon (Scypha), Spongilla (fresh water sponge), Euspongia (Bath sponge)

 PHYLUM CNIDARIA (COELENTERATA): GENERAL CHARACTERS

  1. Grades of organization:
    • Tissue grade.
  2. Symmetry:
    • Radial symmetry.
  3. Germ layers:
    • Diploblastic
  4. Coelom:
    • Acoelomate
  5. Habit and habitat:       
    • Aquatic (mostly marine).
    • Sessile/free swimming.
    • Solitary/colonial.
  6. Digestive system:          
    • Incomplete.
    • Intracellular & extracellular digestion.
  7. Respiratory system:
    • Absent
  8. Circulatory system:
    • Absent
  9. Reproduction:
    • Polyp reproduces asexually (budding) and medusa sexually.
    • Most are separate sexes.
    • External fertilization.
    • Development is indirect.
  10. Unique features:
    • Tentacles with cnidoblasts.
    • Tentacles: Finger-like structures which surrounds the mouth of coelenterates. Used for food capture & defense.
    • Cnidoblasts (Cnidocytes): These are stinging cells (present on the tentacles and the body) with a poison-filled capsule called nematocyst. Cnidoblast is used for anchorage, defense and to capture prey.
    • Gastro-vascular cavity (coelenteron) with an opening (mouth) on hypostome.
    • Polyp & Medusa: 2 types of body forms in cnidarians.
    • Polyp is tubular attached asexual form, with upwardly directed mouth & tentacles. E.g. Hydra, Adamsia.
    • Medusa is umbrella like, free-swimming sexual form, with downwardly directed mouth & tentacles. E.g. Aurelia (Jelly fish).
    • Some shows alternation of generation.
    • Alternation of generation (Metagenesis): The phenomenon in which polyps produce medusae asexually and medusae form the polyps sexually. E.g. Obelia.
    • Corals have skeleton (CaCO3).
Examples
    • Hydra, Obelia, Aurelia, Physalia (Portuguese man of war), Adamsia (Sea-anemone), Pennatula (Sea pen), Gorgonia (Sea fan), Meandrina (Brain coral).

PHYLUM CTENOPHORA (COMB JELLIES): GENERAL CHARACTERS

  1. Grades of organization:
    • Tissue grade.
  2. Symmetry:
    • Radial symmetry.
  3. Germ layers:
    • Diploblastic
  4. Coelom:
    • Acoelomate
  5. Habit and habitat:       
    • Exclusively marine.
    • Solitary & pelagic
  6. Digestive system:          
    • Incomplete.
    • Intracellular & extracellular digestion.
  7. Respiratory system:
    • Absent
  8. Circulatory system:
    • Absent
  9. Reproduction:
    • Only Sexual.
    • Hermaphrodite.
    • External fertilization.
    • Development is indirect.
  10. Unique features:
    • Locomotion is by 8 vertical external rows of ciliated comb plates.
    • Tentacles present.
    • Shows Bioluminescence (property to emit light from the body).
  11. Examples:
    • Ctenoplana, Pleurobrachia.

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