1. Phylum
    2. 1. Classification of Animals
    2. Protozoa
    3. Porifera
    4. Coelenterata
    5. Platyhelminthes
    6. Nemathelminthes
    7. Annelida
    8. Earthworm
    9. Arthropoda
    10. Cockroach
    11. Mosquito
    12. Honey bee and Silk moth
    13. Mollusca
    14. Echinodermata
    15. Hemichordata
    16. Chordata
    17. Pisces
    18. Amphibia
    19. Frog
    20. Reptile
    21. Aves
    22. Mammalia
    23. Rabbit bone
  2. Animal Behaviour and Adaptation
    3. 24. Animal behaviour
    25. Animal adaptation
    26. Migration
  3. Developmental Biology
    4. 27. Development of Animals
    28. Development of Frog
  4. Human Biology
    5. 29. Tissues
    30. Sense organs
    31. Digestive system
    32. Circulatory system
    33. Respiratory system
    34. Nervous system
    35. Endocrine system
    36. Reproductive system
    37. Excretory system
    38. Skeletal system
    39. Basic concept of Immunology
    40. Human diseases
  5. Evolutionary Biology
    6. 41. Origin of Life
    42. Organic Evolution
    43. Theories of Evolution
    44. Evolution of Human beings
    45. Horse Evolution
Phylum
4. Coelenterata
GENERAL CHARACTERS
Image 1
Fig. Hydra
▢ Habitat: Aquatic, mostly marine except few freshwater forms like Hydra
▢ Habit: Sessile or free swimming, Solitary or Colonial
▢ Grade of Organization: Tissue grade of organization
▢ Symmetry: Radial symmetry except Sea anemone which is Biradial symmetrical.
▢ Germ layers: Diploblastic
▢ Body plan: Blind sac body plan
▢ Body wall:
Consists of 2 cellular layers surrounding the Mesogloea
❖ Epidermis (Outer epithelium):
❖ Gastrodermis (Inner epithelium):
  1. Lines the gastrovascular cavity
❖ Mesogloea:
  1. Extracellular gelatinous layer.
  2. Ranges from a thin, noncellular basal lamina to thick, fibrous, jelly-like, connective tissue with or without mesenchymal cells.
▢ Gastrovascular cavity/ Coelenteron:
  1. This cavity serves as gut (for digestion of food) and as circulatory system (for circulation of digested body).
  2. Opens to outside at one end of body to form a mouth.
  3. Mouth serves both in ingestion and egestion.
  4. Anus is absent.
METAGENESIS/ ALTERNATION OF GENERATION
Alternation of polypoid and medusoid generation occurs.
Example
Seen in Hydra of Hydrazoa class
Image 1
Credit. www.w3schools.blog
Image 1
Credit. www.w3schools.blog
Polypoid generation
Medusoid generation
Asexual generation
Sexual generation
No gonads is formed.
Gonads are present.
Sessile
Free swimming
Body is cylindrical with a long stalk.
Body is umbrella, cup shaped with reduced stalk.
Mesogloea is thin.
Mesogloea is thick.
Mouth is located in Hypostome.
Mouth is located in Manubrium.
Diploid
Diploid
POLYMORPHISM
Image 1
Fig. A -> Obelia; B->Hydractinia; C->Vella; D->Physalia;
E->Generalized calycophoran Siphonophora
The occurrence of structurally and functionally different types of individuals, called zooids, within the same organism during its life history is called Polymorphism.
▢ Example: Seen in Physalia of Class of Hydrazoa
▢ 9 types:
❖ Trophozooid/ Gastrozooid: Feeding
❖ Gonophore: Sessile medusae
❖ Gonozooid: Gonophore production
❖ Dactylozooid: Protection, food caption
❖ Tentaculozooid: Same as dactylozooid
❖ Nematophore: Food capture
❖ Pneumatophore: Float
❖ Nectophore: Swimming
❖ Phyllozooid: Protective cover
NEMATOCYST
▢ Cnidocyte/ Cnidoblast: It is cell of cnidarians containing cnide.
▢ Cnide:
  1. Cnide are cellular organelles of cnidocyte.
  2. It is capable of eversion from cnidocyte.
  3. It is of 3 types of which one type is Nematocyst.
METABOLISM
▢ Nutrition:
  1. Cnidarians are carnivorous.
  2. Digestion is extracellular and intracellular.
▢ Skeleton:
  1. Either calvareous or horny
  2. External (Exoskeleton) or Internal (Endoskeleton)
▢ Locomotion: Brought about by smooth muscle fibres.
▢ Respiratory, Circulatory and Excretory systems are absent.:
▢ Nervous system:
  1. Nervous system is a collection of multipolar and bipolar nerve cells forming an irregular net or plexus.
▢ Reproduction:
❖ Asexual methods:
  1. Budding
  2. Strobilation
❖ Sexual methods:
  1. Indirect development by formation of Planula larva.
CLASSIFICATION
Characters
Hydrozoa (Water)
Scyphozoa (Cup shaped Medusa)
Anthozoa (Flower shaped)
Habitat
Few fresh water and most are marine
Marine
Marine
Zooids
Both Polyp and Medusa. In Hydra only Polyp. In Obelia both Polyp and Medusa are present (So Metagenesis)
Medusa
Polyp
Mesogloea
Thin (Dominant) Without chamber
Thick Without chamber
Thin Chambered
Metagenesis
Yes (Both Polyp and Medusa form of zooid present in their life cycle)
No
No
Polymorphism
Yes. E.g.: Physalia (Portuguese man of war):
No
Examples
  1. Hydra
    2. Image 1
  2. Obelia (Sea fur)
    3. Image 1
  3. Physalia (Portuguese man of war)
    4. Image 1
  4. Velella (Little sail)
    5. Image 1
  5. Porpita (Blue button)
    6. Image 1
  6. Mililipora (Fire coral)
    7. Image 1
  7. Bougainvilla (a plant also with same name)
    8. Image 1
  1. Aurelia (Jellyfish)
    • •
      Aurelia is Bioluminiscent.
    Image 1
  1. Metridium (Sea anemone)
    2. Image 1
  2. Adamsia (Sea anemone)
    3. Image 1
  3. Alcyonium (Dead man's finger)
    4. Image 1
  4. Gorgonia (Sea fan)
    5. Image 1
  5. Pennatula (Sea pen/ Sea feather)
    6. Image 1
  6. Fungia (Mushroom coral)
    7. Image 1
  7. Heliopora (Blue coral)
    8. Image 1
  8. Astraea (Star coral)
    9. Image 1
  9. Madrepora (Horny coral)
    10. Image 1
  10. Tubipora (Organ pipe coral)
    11. Image 1
  11. Corallium (Precious Red coral/ Coral stone)
    12. Image 1
  12. Meandrina (Brain coral)
    13. Image 1
  13. Virgularia (Walking stick)
    14. Image 1
  14. Charybdaea (Sea wasp)
    15. Image 1
CELLS
Image 1
Fig. Cells in Hydra
Cell Type
Epidermis
Gastrodermis
Epitheliomuscular cells
Present - Contractile cells that help in movement
Absent
Interstitial cells
Present - Undifferentiated cells that can develop into other cell types
Absent
Nerve cells
Present - Form nerve nets for simple sensory functions
Present - Similar nerve nets found, coordinating with epidermal nerve nets
Cnidocytes
Present - Stinging cells used for defense and prey capture
Absent
Gland cells
Absent
Present - Secrete digestive enzymes into the gastrovascular cavity
Nutrient cells
Absent
Present - Absorb nutrients from digested food
Mucous cells
Present - Secrete mucus to protect the body surface
Present - Secrete mucus for protection and aid in digestion
▢ Cnidocytes:
Image 1
❖ Features of Cnidoblast:
  1. Universal character of all coelenterates.
  2. Derived from interstitial cells of epidermis.
  3. Present only in epidermis.
  4. Maximum in tentacles.
  5. Absent in pedal disc / basal disc.
  6. A group of cnidoblasts is known as Cnidome.
  7. The group of cnidoblasts on the tentacles is especially called Battery.
  8. Opening of nematocyst is Operculum.
  9. Just below the operculum, narrow neck is Butt.
  10. Inside the butt, triangular shaped structure is Barb.
Type and Name
Features and Functions
Penetrant / Stenoteles - Largest Nematocyst
  1. Discharges a thread tube that injects poisonous fluid (hypnotoxin)
  2. Hypnotoxin paralyzes or kills prey like Cyclops and Daphnia
  3. Hypnotoxin is composed of protein and phenol
  4. Makes Cnidarians carnivorous
  5. Most complex type of nematoblast
Volvent / Desmoneme - Smallest Nematocyst
  1. Thread coils tightly around projections such as hair or bristles
  2. Coils and captures prey
Glutinant / Holotrichous isorhiza (Streptoline glutinant) - Largest glutinant
• Used to stick to prey
Glutinant / Atrichous isorhiza (Steroline glutinant) - Smallest glutinant
  1. Helps in looping movement
  2. Common mode of locomotion in Hydra
  3. Looping movement is leech-like in Hydra
  4. Somersaulting movement is the fastest locomotion mode
❖ Grouping of Cnidoblasts:
  1. A group of cnidoblasts is known as Cnidome.
  2. The group of cnidoblasts on the tentacles is especially called Battery.
❖ Structure of Nematocyst:
  1. Opening of nematocyst is Operculum.
  2. Just below the operculum, narrow neck is Butt.
  3. Inside the butt, triangular shaped structure is Barb.
❖ Functions of Nematoblast:
  1. Takes part in locomotion, food capture, offence, and defence.
❖ Nematocyst Details:
  1. Nematocyst or stinging capsule is a part of the cell called Cnidoblast or Cnidocyte.
  2. Nematocyst is known as Independent effector:
  3. Discharge of nematocyst is completely independent of nervous control, hence called independent effector.
  4. Discharge of nematocyst is enzymatic in action.
  5. Discharge involves both mechanical and chemical stimulus.
  6. On stimulation, the nematocyst shoots out within 0.3–0.5 seconds.
  7. Action depends on enzymes that increase osmotic pressure inside the capsule.
  8. Once flagellum is used, it is never withdrawn — nematocyst is used only once.
❖ Supportive Structures:
  1. Lasso, bars (3 pairs of large spines), and barbules (50 pairs of smaller spines).
  2. Lasso helps in checking the emerging of nematocyst.
❖ Cnidocil:
  1. The trigger needle of cnidoblast is called Cnidocil.
  2. Cnidocil is the stimulus-receiving part of nematoblast / cnidoblast.
▢ Interstitial cell:
❖ About:
  1. Interstitial cell is a totipotent cell.
  2. So, interstitial cells help in regeneration called Morpholaxis.
  3. Interstitial cell can transform into all other types of cells including germ/sex cell, glandular cell, and cnidoblast.
❖ Cell Types Derived from Interstitial Cells:
  1. Reproductive cells
  2. Glandular cells
  3. Stinging cells (Cnidoblasts)
❖ Scientific View:
  1. Brien stated that all cells arise from interstitial cells.
❖ Functions of Interstitial Cells:
  1. Help in formation of external bud.
❖ Characteristics of Interstitial Cells:
  1. Interstitial cells are uninucleated.
  2. Interstitial cells are absent in the epidermis of pedal disc and tentacles.
  3. Interstitial cells can cross the mesoglea.
▢ Epithelio-muscular cell:
❖ Epithelio-muscular Cell:
  1. Epithelio-muscular cell forms the bulk of the epidermis.
❖ Structure of Epithelio-muscular Cell:
  1. Muscle tail or Myoneme is present in it.
  2. The number of myonemes in the muscle tail of epithelio-muscular cells is two.
❖ Function of Epithelio-muscular Cell:
  1. Contraction of muscle fibres in the epithelio-muscular cells shortens the body and tentacles.
Part
Features and Functions
Epithelial Part
  1. Located towards the epidermis side
  2. Helps in cuticle formation (Cuticle → Epidermis → Mesoglea → Endodermis)
  3. Provides protection
Muscular Part
  1. Located towards the mesoglea side
  2. Helps in shortening and bending of the body
  3. Responsible for body movement
▢ Epithelio-gland cell:
❖ Epithelio-gland Cells / Glandulo-muscular Cell:
  1. Also known as Glandulo-muscular cell
  2. Glandulo-muscular cell is a modification of epithelial-muscular cells.
  3. Glandulo-muscular cell is maximum in epidermis, pedal/basal disc.
❖ Functions of Glandulo-muscular Cells:
  1. Help in attachment.
  2. Create gas bubbles that make it float (floating movement).
▢ Sensory cell:
❖ Sense organs like Statocyst, Tentaculocyst occur in free swimming forms.
1.
▢ Nerve cell:
❖ Nerve Cell:
  1. Nerve cells are apolar.
  2. Nerve cells are more numerous in the epidermis of hypostome, basal disc, and basal parts of tentacles.
❖ Stimuli Responded to by Nerve Cells:
  1. Touch
  2. Chemical
  3. Temperature
  4. Light
  5. Electric current
  6. No response to rheotaxis
❖ Nervous System:
  1. Nervous system is a simple nerve net, made of naked and largely nonpolar neurons.
❖ Endocrine Role:
  1. Endocrine system is also present, and hormones are secreted by nerves.
▢ Germ cell:
SPECIAL POINTS
▢ Special Points:
  1. Hydra has direct development, but a larva-like structure is present called Hydraula or Hydratuba.
  2. Common larva of cnidarians is Planula, especially in jellyfish, Obelia, and sea anemone.
▢ Symbiotic Relationships:
  1. Sea anemone (Metridium) and hermit crab: Commensalism (+, 0).
  2. Euplectella and Spongicola: Commensalism (+, 0).
  3. Hydra and Zoochlorella or Zooxanthophylla: Symbiosis (+, +).
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Multiple Choice Questions

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[MOE 2054]

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[IOM 2005]

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[IOM 2005]

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[IOM 2002]

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[MOE 2063]

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[BPKIHS 2001]

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[BPKIHS 2005]

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[IE 2002]

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[IE 2005, IOM 2068]

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[IOM 2013]

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[BPKIHS-2013,2014]

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[BPKIHS-2013]

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[IOM-2014]

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[IOM-2013]

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[IOM-2016]

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