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KINGDOM ANIMALIA Phylum Cnidaria. Phylum Cnidaria. The phylum name comes from Cnidaria , the Greek word for nettle, a plant that has stinging hairs. Members of the Phylum Cnidaria. …exhibit radial or biradial symmetry. …are all aquatic (typically marine, but some freshwater).
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Phylum Cnidaria • The phylum name comes from Cnidaria, the Greek word for nettle, a plant that has stinging hairs.
Members of the Phylum Cnidaria • …exhibit radial or biradial symmetry. • …are all aquatic (typically marine, but some freshwater). • …are sessile, free-floating, or weak swimming. • …have a tissue-level organization. • …have a primitive nervous system. • …have stinging cells.
Question Which of the following characteristics sets the members of the phylum Cnidaria apart from all other animals? • They are all aquatic. • They have stinging cells. • They are all multicellular. • They are sessile as adults.
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.
Question In a cnidarian, the jelly substance in between the two cell layers is called • mesoglea • cnidoglea • epidermis • gastrodermis
Reproduction • Sexual reproduction: gametes are shed directly into the water. • Asexual reproduction: usually by budding, some by fission.
Question Cnidarians reproduce in all of the following ways, EXCEPT • Asexual fission • Asexual budding • Sexual regeneration • Sexual reproduction involving egg and sperm
Life Cycles:Polyp and Medusa • Cnidarians generally alternate between sessile polyps that reproduce asexually and swimming medusae that reproduce sexually. • One of these stages is missing in many forms.
Question True or False: This picture represents the medusa body plan of a cnidarian.
Stinging Tentacles • 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.
Question In a cnidarian, the cnidocytes are used for • swimming • digesting food • paralyzing prey • sensing predators
Feeding and Digestion • 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.
Question Where does digestion take place for cnidarians? • In the tentacles • In the epidermis • Outside the body • In the gastrovascular cavity
Four Important Cnidarian Classes 1. Class Hydrozoa • Mostly marine • Alteration of generation (polyp and medusa stages) is usually exhibited • Includes hydroids, fire corals, and Portugese man-of-war
Four Important Cnidarian Classes 2. Class Scyphozoa • Dominant stage is the medusa • Polyp is absent or reduced • Cup-shaped umbrellas • Includes true jellyfish
Four Important Cnidarian Classes 3. Class Cubozoa • 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.
Four Important Cnidarian Classes 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.
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.
