1. CHAPTER 13
Phylum Cnidaria

3. General Characteristics
Phylum Cnidaria
Fossil specimens dated to over 700 million years ago
General Characteristics
Soft bodied
Carnivorous
Stinging tentacles
Examples: Jellyfish, sea anemones

4. Phylum Cnidaria Classes of Cnidaria
Hydrozoa (Portuguese Man-of-War, Hydra)
Scyphozoa (True Jellyfish - Aurelia)
Anthozoa (Sea Anenome, Corals)

5. Phylum Cnidaria Characteristics of Phylum Cnidaria
All are aquatic and mostly marine
Symmetry
Radial
Two body types
Free-swimming medusa
Sessile polyps
Acoelomates - No coelom
Diploblastic
Blind (Incomplete) Gut

6. Phylum Cnidaria Mechanism of Nematocyst Discharge
Tentacles usually encircle mouth or oral region
Equipped with specialized cells: cnidocytes
Cnidocytes: stinging cells located on their tentacles
Nematocyst: stinging organelle, poison-filled structure that contains a tightly coiled dart.
Tactile stimulation of cnidocil, causes nematocyst to discharge
After discharge, cnidocyte is absorbed and another develops
Mechanism of Nematocyst Discharge
When stimulated, water rushes into the capsule
The operculum (cap) opens and rapidly launches the filament
Barbs inject poison into prey
Only a few jellyfish - and the Portuguese man-of-war can seriously harm humans

7. Cnidarian Phyla Topical Solutions if stung: acidic (vinegar)
Urine - only if urine is acidic?? Most urine is sterile.
Apply heat or ice for pain (also denatures toxins)
Salt water should be applied to remove any excess toxins.

8. Discharged
cnidae
recoiled

9. Phylum Cnidaria OTHER CNIDARIAN CHARACTERISTICS
Sense organs for balance (statocysts) and photosensitivity (ocelli)
Nerve net
Simple nervous system, no brain
Asexual reproduction
Budding in polyps
Sexual reproduction
By gametes in all medusa and some polyps
Monoecious or Dioecious
No excretory or respiratory system

10. Phylum Cnidaria Life Cycles Hydrazoan Life Cycle
Typically, zygote develops into a motile planula larva
Planula settles, and metamorphoses into a polyp
Produce other polyps asexually
Polyps eventually produce a free-swimming medusa by asexual reproduction (Budding)
Hydrazoan
Life Cycle
13-10

11. Hermit crab uses cnidarian as protection
Showing growth on host shell

13. Phylum Cnidaria Form and Function
Cnidaria have two basic body plans: polyp and medusa
Polyp
Adaptation to a sedentary life
Tubular body with the mouth directed upward and surrounded by tentacles
Mouth leads into a blind-gut cavity
Reproduce asexually by budding, fission, or pedal laceration

14. Phylum Cnidaria - Medusa
Bell or umbrella-shaped
Usually free-swimming
Mouth directed downward
Tentacles may extend down from rim of umbrella

15. Phylum Cnidaria Body Wall Cnidarian body Outer epidermis
Inner gastrodermis (gastrovascular cavity = gut)
Layers separated by mesoglea
Mesoglea
Gelatinous (at least 95% water) - jellylike
Continuous, extending through body and tentacles
Supports body
Thickness varies
13-12

17. Class Hydrozoa Phylum Cnidaria
Most marine and colonial with both polyp and medusa forms (polyp form dominates)
Colonial Obelia
Typical hydroid has a base, a stalk, and one or more individual polyp animals
Feeding polyps with tentacles around mouth= hydranths
In Obelia, the medusa buds are formed by a reproductive polyp called a gonangium

18. Obelia Life Cycle

19. Hydroids

20. Bell medusa
(Hydroid)

21. Medusa
D. Developing Polyp from Planula: Frustule = bud

22. Freshwater
Hydrozoan

23. Class Hydrozoa: Animals
Phylum Cnidaria
Class Hydrozoa: Animals
Hydra
Found in fresh water
Worldwide distribution (16 species in North America)
Polyp body form
Ring of 6–10 hollow tentacles encircles mouth
Portuguese Man-of-War
Floats on surface (air bladder)
Tentacles reach up to 10 meters
Contains polyp colonies and medusa
Air bladder contains gases released
13-23

24. Hydra catching a water flea

25. Hydra w/ developing bud and ovary/egg

26. Portuguese man-of-war Colony
Secrete powerful neurotoxin - Class Hydrozoa (Many Polyps and medusa in colony)

27. Differences between Hydrozoa and Scyphozoa
Colonial Stages
Mostly Polyp life form
Medusa, if present, are usually small
Small amounts of mesoglea
Less tentacles
Scyphozoa
Large Medusa forms
Cells present in mesoglea
More complex
More tentacles
Large amount of mesoglea

28. Class Scyphozoa Phylum Cnidaria
Most of the larger jellyfishes belong to this class
Nearly all float in open sea
Bells vary in shape and size
Composed mostly of mesoglea

29. Class Scyphozoa
Giant jellyfish
exceeds 2 Meters
in diameter

30. Moon
Jellyfish
(Aurelia)

31. Phylum Cnidaria - Scyphozoa
Reproduction methods
Asexual - Similar to other cnidarians. Budding
But also use Strobilation - asexual budding of saucerlike buds that develop into medusa.

32. Life Cycle of Aurelia, marine scyphozoan
Strobilation

33. Class Anthozoa Phylum Cnidaria Lack a medusa stage
All marine, in both deep and shallow water, and vary in size
Examples: sea anemones, sea corals

34. Sea Anemones

35. Structure of Sea Anemone

36. Phylum Cnidaria - Anthozoa
Sea Anemones
Polyps larger and heavier than hydrozoan polyps
Attach to shells, rocks, timber, etc. by pedal discs
Crown of tentacles surrounds the flat oral disc
When in danger, water rapidly expelled through pores as the anemone contracts to a small size

37. Sea Anemone being attacked by a Sea Star
Can Sea Anemones run?

39. Tube Anemone
13-39

40. Phylum Cnidaria - Anthozoa
Reproduction of Sea Anemones
Some dioecious, some monoecious
Monoecious species - produce sperm first and eggs later
Fertilization is external or in gastrovascular cavity
Zygote becomes a ciliated larva
Pedal laceration, small pieces of pedal disc break off and regenerate a small anemone
Budding can occur

41. Closed during day, open to feed at night

42. Polyp of
Coral

43. A Thorny Coral

44. A soft coral on Pacific Coral Reef

45. Horny Coral Types
Red Gorgonian
Sea Fan
Red Whip Coral

46. Coral Reefs Phylum Cnidaria
Great diversity of organisms (under rainforest)
Plants and animals are limited to top layer
Above the calcium carbonate deposits
Reef forming corals and algae precipitate calcium carbonate to form most coral reefs
Require warmth, light, and salinity of undiluted sea water (contains calcium)
Photosynthetic zooxanthellae live in their tissues
Provide food for corals, carbon for calcium carbonate, and recycle phosphorus and nitrogenous wastes

47. Phylum Cnidaria - Human Impact
Nutrients from fertilizer and sewage threaten coral reefs with excessive algal growth - or by killing zooxanthellae, which leads to coral bleaching.
Persian Gulf reefs have withstood surprising amounts of oil pollution
Coral reefs in many areas are threatened by factors mostly of human origin