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Cnidarians
Phylum Cnidaria:
Jellies, anemones, corals and hydroids
Mrs. Covington: Marine Biology
Basic Facts
• Simple:slightly more complex than sponges
• Radial Symmetry: no head, front or back; looks the same from every side
• Abundant: Nearly 10,000 species
(mostly found in warm, marine habitats)
Body Layers
• Body wall consists of 2 layers separated by jelly
Layer 1: ECTODERM- muscle, nerve, or thread cells called nematocysts
NEMATOCYST: contains stinging cells (cnidoblasts)with neurotoxic poison, used for defense and food capture.
Body Layers cont…
• Layer 1 and 2 are separated by the Mesoglea, a non-cellular, gel colloid
• Layer 2: ENDODERM- Digestion and absorption of food
Body Parts (sides)
• Part 1: Oral- Digestive cavity, sac-like, the open end is the mouth
• Part 2: Aboral- Tentacles located around mouth, used to catch food and assist in movement
Oral
Aboral
Diagram: Showing oral and aboral parts
aboral
BOTTOM VIEW OF BODY
Oral (mouth area)
Aboral (tentacle area)
2 Body Forms (Stages)
• POLYP- mouth & tentacles face up, most are sessile
• MEDUSA- mouth & tentacles face down, free swimming
Jelly Reproduction
• Jellies are either male or female and reproduce sexually by releasing sperm into the water.
• Corals (& hydroids) may reproduce sexually by releasing egg and sperm or asexually by budding or fragmentation
Jellies are either male or female and reproduce sexually by releasing egg & sperm into the water.
Coral (& Hydroid) Reproduction
• Asexually by budding or fragmentation
• Sexually by releasing egg and sperm
Practice Body Parts (Sides)
Practice Body Forms (Stages)
CORAL REEFS: The most densely populated ecosystem on earth!
Types of Reefs
1. Fringing Reef- Grows close & parallel to shore as a narrow band (inner reef is flat, outer reef is sloped)
2. *Barrier Reef- Farther off shore than fringing & separated by a lagoon. Parallel to shore, may be exposed at low tide
Andros Barrier Reef: 140 miles long!
(3rd longest in the world )
Visible from east shore of Andros on the horizon…look for waves breaking.
Reef types cont…
3. Atolls- Ring of reef with steep outer slopes enclosing a shallow lagoon
4. *Patch Reef- Small, isolated growths of reef that usually form between fringing or barrier reef and the shore.
Fringing Reef
Barrier Reef
Atolls
Patch Reef
Illustration of Reef Types
Conditions for Reef Growth
• Hard Surface
• Shallow Water (165 ft. or less)
• Warm Water (about 68° F)
• Clear Water
*Coral can grow ½ in. per year in good conditions!
*Which side of Andros will have coral?
Importance of Algae to Coral
• Coral exhibits mutualistic symbiosis with Zooxanthellae Algae (dinoflagellates)
• Photosynthetic Dinoflagellates nourish corals with sugars which help them produce limestone corallite
• Corals feed mainly on zooplankton, with the help of zooxanthellae
Competition, Predation, & Disease
• Corals may be overgrown by a different creature competing for space & light
• Some creatures attack coral, destroying it
• Some creatures eat coral but don’t destroy it, others graze heavily
Coral Aggression
• Corals will send out filaments to attack and digest another coral in its way! This would be an example of competition for space (light).
Competition, Predation, & Disease cont…
• Coral bleaching: If stressed, corals expel algae causing loss of color. If algae are regained, it may recover
• Black-Band Disease caused by Cyanobacteria, kills coral as it grows
• Pollution
• Natural death by unknown causes
Man using dynamite to either blow up coral to sell or to kill reef fish…very, very bad!
THE END