The document summarizes key characteristics of the phylum Cnidaria. It includes jellyfish, anemones, corals, hydroids and has over 10,000 species. Cnidarians have diploblastic tissues and a gastrovascular cavity with a single opening. They possess stinging cells called cnidocytes that are used to capture prey. Cnidarians have both polyp and medusa life stages and can reproduce sexually or asexually. The phylum is divided into four classes: Hydrozoa, Scyphozoa, Cubozoa, and Anthozoa.

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.