Explanation of phylum cnidaria

1. Phylum Cnidaria

2. Includes
• Jelly fish
• Anemones
• Corals
• Hydroids
• 10,000 species
• Diploblastic tissues level organization.

3. Habitat
A. Aquatic
1. Most Marine
2. Few fresh-water

4. • Internal sac for digestion called gastrovascular
cavity
• One opening which serve as mouth/anus.
• Cells of epidermis and gastrodermis
differentiated into different cell types for:
• Movement
• Protection
• Food gathering
• Digestion

6. Characteristic feature of cnidarians is Cnidocytes
Contain Cnidea (commonly known as
Nematocyst)
Nematocyst is a capsule enclosing coiled thread
with barbs and spines.
Operculum caps the capsule.
Modified cilium called Cnidocil

7. • Cnidocil receive stimulus from prey/enemy.
• Nematocyst discharge initiated by opening of
operculum.
• Thread comes out in twisting motion with
enormous speed and penetrate the prey body.
• Spines/barbs help to anchor into the prey.

10. Cnidarian have two body form in
their life cycle
Polyp:
1. Polyp:
• Sessile stage
• Attach at aboral end
• Asexual stage
• Cylindrical body
• Mouth pointed upward
Medusa:
2. Medusa:
• Free-swimming stage
• Mouth pointed downward
• Sexual stage
• Body is like inverted
bowl
• Usually dioecious

14. Reproduction
• Gametes produced by medusa
• After fertilization zygote formed
• Zygote transformed to planula larva
• Larva will form polyp
• Polyp reproduced by budding
• Bud may detach or remain attach to parent, forming colony
gametes zygote
Planula
larva
polyp bud

18. Maintenance of Function
• Gastrovascular cavity carry out theses
functions:
Digestion
Exchange of gases
Removal of waste material
Discharge of gametes

19. • Feeds on crustaceans
• On contact to prey, nematocyst discharged and
paralyze the prey
• Tentacles draw the food into mouth and then to
gastrovascular cavity
• Gastrodermal enzymes help in digestion
• Indigested material ejected through the
opening
• Gas exchange and excretion takes place by
diffusion process

20. • Cnidarians have hydrostatic skeleton
• Hydrostatic skeleton is water or fluid filled
cavity, against which the contractile elements
of the body wall acts
• It give support to cnidarians body
• Gastrovascular cavity act as a hydrostatic
skeleton
• Epitheliomuscular cells are contractile cells,
help in movement of polyp and medusa

21. • Cnidarians have nerve cells.
• Sensory structure distributed throughout the body.
• It has receptors for touch.
• Epidermis and gastrodermis both possess nerve cells.
• These nerve cells interconnected to form network
called as Nerve Net.
• Some species have Nerve Ring.

22. Classification
Phylum Cnidaria is divided into four major
classes.
1. Class Hydrozoa.
2. Class Scyphozoa.
3. Class Cubozoa.
4. Class Anthozoa.

25. Class Hydrozoa
• Mostly marine, some fresh-water.
• Some hydroid lost medusa stage.
• Gametes released outside the body.
• Mesoglea is acellular.
• Colonial formation.
• Entire colony has continuous gastrovascular
cavity.
• Feeding polyp called Gastrozoids.
• Reproductive polyps called Gonozoids.

26. Hydra
• Typical cnidarian body.
• Cnidocytes present in epidermis.
• One opening surrounded by tentacles.
• Attached aborally by pedal disc.
• Lacks medusa stage.
• Reproduced by budding of polyps.
• Sexual reproduction occurs also in polyps.
• Epidermal cells will form ovaries and testes that
release eggs and sperms.
• After fertilization, zygote develop into adult hydra.

28. Class Scyphozoa
• Exclusively marine true-jelly fish.
• Medusa is dominant stage.
• Mesoglea contain mesenchyme cells.
• Cnidocytes present in epidermis and
gastrodermis.
• Gametes released in gastovascular cavity.
• Dioecious.
• Common example is Aurelia.

30. Class Cubozoa
• Marine box-jelly fish.
• Similar to scyphozoan.
• Square-shaped or cuboidal-shaped.
• Four tentacles hang from each corner.
• Active swimmer.
• Polyps and medusa both present in life cycle.

32. Class Anthozoa
• Marine, colonial or solitary.
• Lack medusa stage.
• Mouth lead to pharynx.
• Gastrovascular cavity divided into mesentaries
containing cnidocytes and gonads.
• Mouth surrounded by tentacles.
• Tentacles function to protect and catch food.

33. • Common anthozoans sea anemones.
• Monoecious/dioecious.
• Fertilization may be external/gastrovascular
cavity.
• Zygote develop into planula larva
• Larva develop into adult animal.

35. • Another common anthozoans are coral.
• Similar to anemones.
• Secrete cup-shaped exoskeleton.
• Made of calcium carbonate.
• Sexual reproduction similar to anemones.
• Asexually by budding, live in colony.
• Common examples sea fans, red corals.

37. Brain Corals

38. Phylum Ctenophora
• Commonly known as comb-jellies/sea walnuts.
• ~ 90 species.
• Diploblastic.
• Gelatinous layer between epidermis and
gastrodermis.
• Gastrovascular cavity present.
• Nerve net present.

39. • 8 rows of comb-like paddles
• Paddles contain thousands of cilia for
swimming.
• Adhesive cells colloblast for protection and
feeding.
• Ctenophores have two openings.
• Regenerate their lost parts.
• Monoecious.
• Fertilization external.
• Larva develops into adult.

41. Classification
1. Class Tentaculata:
• Have two tentacles.
• Large mouth parts.
2. Class Nuda:
• Lacks tentacles.
• Swim with plankton.