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Fascinating World of Phylum Cnidaria: Characteristics and Life Cycles

Explore the diverse world of Phylum Cnidaria with soft-bodied, carnivorous creatures like jellyfish and sea anemones. Dive into their unique forms, reproductive strategies, and defense mechanisms.

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Fascinating World of Phylum Cnidaria: Characteristics and Life Cycles

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  1. CHAPTER 13 Phylum Cnidaria

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

  3. Phylum Cnidaria • Classes of Cnidaria • Hydrozoa (Portuguese Man-of-War, Hydra) • Scyphozoa (True Jellyfish - Aurelia) • Anthozoa (Sea Anenome, Corals) • Cubazoa (Box Jellies-- Poison)

  4. 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

  5. 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

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

  7. Phylum Cnidaria • 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 • Box Jellyfish - and the Portuguese man-of-war can seriously harm humans

  8. 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.

  9. Discharged cnidae recoiled

  10. 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

  11. Phylum Cnidaria Life Cycles • 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 13-13

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

  13. 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

  14. Phylum Cnidaria Class Hydrozoa • 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

  15. Obelia Life Cycle

  16. Hydroids

  17. Bell medusa (Hydroid)

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

  19. Freshwater Hydrozoan

  20. 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

  21. Hydra catching a water flea

  22. Hydra w/ developing bud and ovary/egg

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

  24. Hydrozoa 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 Differences between Hydrozoa and Scyphozoa

  25. Phylum Cnidaria Class Scyphozoa • 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

  26. Class Scyphozoa • Giant jellyfish • exceeds 2 Meters • in diameter

  27. Moon Jellyfish (Aurelia)

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

  29. Life Cycle of Aurelia, marine scyphozoan Strobilation

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

  31. Sea Anemones

  32. Structure of Sea Anemone

  33. 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

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

  35. Tube Anemone 13-39

  36. 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

  37. Closed during day, open to feed at night

  38. Polyp of Coral

  39. A Thorny Coral

  40. A soft coral on Pacific Coral Reef

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

  42. Phylum Cnidaria • Coral Reefs • 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

  43. Phylum Cnidaria - Human Impact 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

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