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