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Phylum Cnidaria
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Phylum Cnidaria The phylum name comes from Cnidaria, the Greek word for nettle, a plant that has stinging hairs.
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Cladogram of Cnidaria Anthozoa Scyphozoa Cubozoa Medusa cuboidal
Loss of medusa Hydrozoa Polyp stage reduced Septa divide gastrovascular cavity Radial symmetry, cnidocytes, planula larva 5
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Characteristics exhibit radial or biradial symmetry.
are all aquatic (typically marine, but some freshwater). gas exchange through diffusion are sessile, free-floating, or weak swimming. have a tissue-level organization. have a primitive nervous system. have stinging cells. heterotrophic ectothermic
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Radial symmetry 7 7
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General Organization Cnidarian bodies are organized around the gastrovascular cavity, where digestion takes place. Two layers of cells: gastrodermis (lining the digestive tract) and epidermis (outer layer) Mesoglea: jelly substance in between the two cell layers.
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cnidocytes (which contain nematocysts)
The cell types. contracting cells nerve cells cnidocytes (which contain nematocysts) gastrovascular cavity mouth mesoglea tentacle oral arms gastrovascular cavity mouth mesoglea tentacle oral arms gastrovascular cavity mouth mesoglea tentacle oral arms gastrovascular cavity mouth mesoglea tentacle oral arms gastrovascular cavity mouth mesoglea tentacle oral arms barbs coiled nematocyst discharged 9
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Nervous System Nerve cells, arranged in a nerve net. 10
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Body Plan Two body forms Polyp
In the polyp form of a coral, the tentacles and mouth face upward. Medusa In the medusa form of a jellyfish, the tentacles and mouth face downward.
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Fig. 13.2 Fig. 13.2 12 12
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Nutrition The tentacles of all cnidarians produce nematocysts, organelles that can discharge threads to entangle, penetrate, or poison prey. The tentacles are composed of cells called cnidocytes, which contain the nematocysts. Cnidarians prey on a variety of appropriate-sized prey. Prey is normally drawn into the gastrovascular cavity by the tentacles. Here, gland cells discharge enzymes onto the food.
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Cnidocyte Structure and Nematocyst Discharge
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Reproduction/Life Cycle
Sexual reproduction: gametes are shed directly into the water. Asexual reproduction: usually by budding, some by fission. Cnidarians generally alternate between sessile polyps that reproduce asexually and swimming medusae that reproduce sexually. One of these stages is missing in many forms.
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Four Important Cnidarian Classes
The four major cnidarian classes are defined by their dominant body form. Class Hydrozoa Class Scyphozoa Class Cubozoa Class Anthozoa
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1. Class Hydrozoa Hydrozoans such as hydra alternate between forms.
Includes hydroids, fire corals, and Portugese man-of-war
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Class Hydrozoa Freshwater & marine.
Cnidocytes present only on epidermis. Medusa (if present) with a muscular velum. Mesoglea without ameboid cells. Asexual reproduction by budding. Sexual reproduction via gametes produced by epidermis & released into water. 20
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Class Hydrozoa Genus Hydra Obelia Gonionemus Physalia 21
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Hydra Encapsulated embryo Ovaries Budding Spermaries Sexual cycle
Asexual cycle 22 22
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Hydra Gastrovascular cavity Gastrodermis Mesoglea Epidermis Body Wall
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Obelia Gonangium Medusae Medusa bud 24
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Fig. 13.9 25 25
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Gonionemus Fig b 26 26
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Gonionemus Velum 27
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Physalia 28
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Portuguese Man of War - cnidarian that floats in the water and has long tentacles
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2. Class Scyphozoa The class name Scyphozoa comes from the Greek word skyphos denoting a kind of drinking cup shape of the organism and alluding to the cup Dominant stage is the medusa Polyp is absent or reduced Cup-shaped umbrellas Includes true jellyfish
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Tentacles up to 70 meters in length
Cnidocytes present in gastrodermis & epidermis Thick mesoglea contains ameboid cells Gametes produced by gastrodermis All marine 31
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Genus: Aurelia labiata
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Aurelia Mesoglea Eggs Gastrovascular cavity Mouth 33 33
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Aurelia Oral arm Gastric pouch Mouth Tentacles 34
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Aurelia 35
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Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Aurelia Life History 36
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Fig Fig 37 37
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Planula Larva Ciliated larva that can swim to a new location 38 38
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3. Class Cubozoa Cubozoans such as sea wasps have a dominant medusa form. Like jellyfishes, but they have cubical umbrellas. Some may deliver fatal stings. Includes the box jelly, one of the 10 most venomous organisms on earth.
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Tentacles arise at four corners from blade-like pendalium.
All marine Strong swimmers which prey primarily on fish Stings of some may be fatal within minutes to humans. Ex) 7 pounds movie 40
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Class Cubozoa Gonad Pedalium Tentacle 41 41
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Genus Chironex Sea Wasp
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4. Class Anthozoa Polyps with a flowerlike appearance No medusa stage All marine, found all over the world Includes sea anemones, corals, sea fans, and sea whips.
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Some produce protective skeletons
Solitary or colonial Some produce protective skeletons Gastrovascular cavity subdivided by at least 8 mesenteries Cnidocytes on mesenteries Mesoglea contains ameboid cells 44
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Genus Metridium Sea Anemone
Tentacles Mouth Pharynx Septum Gastrovascular cavity 45 45
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Symbiosis 47
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Sea Anenome Fighting MCDOUGALL VIDEO CH 14 PREDATOR PREY 1 - ANEMONE
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Class Anthozoa Corals Protective skeleton of calcium carbonate
Polyp retracts when not feeding 49
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Corals Colony of interconnected polyps
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Zooxanthellae Symbiotic Photosynthetic dinoflagellates (brown)
Live in corals Provide nutrients for coral by photosynthesis Mutualism 51
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Genus Meandrina Brain Coral
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Order Gorgonacea Sea Fan
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Genus Tubipora Pipe Organ Coral
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Genus Actinodiscus Mushroom Coral
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Genus Acropora Staghorn Coral
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Coral Reefs Formed over thousands of years from successive layers of coral skeleton deposits (calcium carbonate forms underwater mountains of coral animal skeletons) The underwater equivalent of the amazon jungle- very high species diversity and biomass Reefs contain sponges, colonial hydrozoans, anemones, many varieties of coral, fish, many types of worms we’ve not discussed, not to mention bryozoans, ctenophores, protists, bacteria, etc etc.. 57
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Economic Importance Reef-building corals provide habitat for fish and other animals that are important as food sources for humans. Coral reefs are tourist attractions and coral rocks are used as building materials and jewelry.
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Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Coral Reef Ecosystem 59 Photo © McGraw-Hill Higher Education, Barry Barker, Photographer
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The End 60
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Which is a… Coral (Anthozoa) Box Jelly (Cuboza) Hydra (Hydrozoa)
True Jelly (Scyphozoa) 61
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Which is a… Coral (Anthozoa) Box Jelly (Cuboza) Hydra (Hydrozoa)
True Jelly (Scyphozoa) 62
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Which is a… True Coral (Anthozoa) Box Jelly (Cuboza) Hydra (Hydrozoa)
True Jelly (Scyphozoa) True 63
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Which is a… True Coral (Anthozoa) Box Jelly (Cuboza) Hydra (Hydrozoa)
True Jelly (Scyphozoa) True 64
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Which is a… True Box Coral (Anthozoa) Box Jelly (Cuboza)
Hydra (Hydrozoa) True Jelly (Scyphozoa) True Box 65
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Which is a… True Box Coral (Anthozoa) Box Jelly (Cuboza)
Hydra (Hydrozoa) True Jelly (Scyphozoa) True Box 66
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Which is a… True Box Coral Coral (Anthozoa) Box Jelly (Cuboza)
Hydra (Hydrozoa) True Jelly (Scyphozoa) True Box Coral 67
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Which is a… True Box Coral Coral (Anthozoa) Box Jelly (Cuboza)
Hydra (Hydrozoa) True Jelly (Scyphozoa) True Box Coral 68
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Which is a… Hydra True Box Coral Coral (Anthozoa) Box Jelly (Cuboza)
Hydra (Hydrozoa) True Jelly (Scyphozoa) Hydra True Box Coral 69
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