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Phylum Cnidaria &
Phylum Ctenaphora
Jellyfish, Sea Anemones, Coral, Hydra,
Sea Fans and Sea Wasps
Comb Jellies
General Characteristics
Of Cnidarians
-Soft bodied
-Carnivorous
-Stinging tentacles
-Examples: Jellyfish, sea anemones,
hydras, corals
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Classes of Cnidaria
Hydrozoa - Portuguese man-of-war, hydra
Scyphozoa - true jellyfish – Aurelia
Anthozoa - sea anenome, corals, sea fans
Cubozoa – sea wasps, aka box jellies
Characteristics of Phylum Cnidaria
- all aquatic; mostly marine
- radially, or biradially symmetrical
- acoelomate - no coelom
- diploblastic – (two germ layers)
- blind (incomplete) gut
- 2 body types –
free-swimming medusa
sessile polyps
Characteristics of Cnidarians (con’t)
- tentacles - around mouth/oral region
- have specialized stinging cells – cnidocytes
Cnidocytes have organelles called cnidae.
Cnidae - over 30 types
-some are sticky and serve as an anchor
-some are toxic
- a cnidarian may have more than 6 types!
Nematocysts - most common type of cnida
- used to inject a toxin
- used for defense and to
capture prey
Only a few jellyfish, ex. Portuguese
man-of-war, can seriously harm
humans
Characteristics of Cnidarians (con’t)
statocyst - sensory organ for balance
ocelli - photosensitivity
nerve net, simple system, no brain
neurons sense physical contact
reproduction
asexual - budding in polyps
sexual - in all medusae & some polyps
monoecious or dioecious
No excretory or respiratory system
Cnidarian body plans:
Polyp
-internal body cavity
-adaptation to a sedentary life
-tubular body; mouth directed upward and
surrounded by tentacles
-reproduce asexually by budding, fission, or
pedal laceration (sea anemones); sexually
by broadcasting sperm & egg into water
Medusa
- bell or umbrella-shaped
- usually free-swimming
- mouth directed downward
- tentacles may extend down from
rim of medusa
- statocysts for balance or direction
- ocelli for light/vision
Cnidarian Body Wall
Outer epidermis
mesoglea
Inner gastrodermis
Gastrovascular cavity (gut)
Nematocyst discharged - seen by
scanning electron microscope
Kingdom Animalia – Cnidaria
All cnidarians have specialized stinging or adhesive structures called cnidae
Discharge
acceleration is
at 40,000g!!!
When triggered, the the cnidocyte cells
discharge the cnidae. A specialized form
of cnidae called the nematocyst, has a
harpoon like structure that enters the
flesh of the potential predator or prey,
releasing neurotoxins.
Need both physical and chemical stimulation to induce release. Why do you think this is?
Feeding and Digestion
Polyps
-Typically carnivorous
-Catch prey with tentacles ; pass them to
gastrovascular cavity
-Gland cells discharge enzymes to begin
extracellular digestion
-Intracellular digestion continues in gastrodermis
Class Hydrozoa: Animals
Hydra
Found in fresh water
Worldwide distribution (16 species in North America)
Body is a cylindrical tube
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
Class Anthozoa
Corals
Secrete calcium carbonate to form “exoskeleton”
- reef builders
- attach to solid structures
- zooxanthellae
Sea Fans or Sea Whips
Secrete gorgonin, a more flexible substance than calcium
carbonate
- attach to sea bottom, sand
- zooxanthellae
Characteristics of Ctenophora
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Long classified as jellyfish, recently recategorized
Only animal that swim by means of cilia
Range from a few millimeters to 1.5 m in size
Layer of epidermis and gastrodermis with layer of
mesoglea (jelly) between – single in Cnidarians,
double in Ctenophora
 Nerve net
 Specialized colloblast cells as opposed to nematocysts
 Most are hermaphroditic
 Does possess an anal pore though most material is
ejected through the main
 Often prey of turtles and jellyfish