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.

• Topic 1: Basis of Classification
• Topic 2: Porifera, Cnidaria, Ctenophora
• Topic 3: Platyhelminthes, Aschelminthes
• Topic 4: Annelida, Arthropoda
• Topic 5: Mollusca, Echinodermata, Hemichordata
• Topic 6: Chordata - up to Sub phylum Vertebrata
• Topic 7: Chordata - Cyclostomata, Pisces
• Topic 8: Chordata - Tetrapoda