Corals, Anemones, Sea Fans, and Jellies

Phylum CnidariaThe Stingers

Box Jellyfish - Irukandji - YouTube

Characteristics

• Radially symmetrical: repeating units around a central point

Characteristics continued• Mesoglea: layer of

jelly separating two tissue layers of cup or umbrella-shaped body

• Gastrovascular cavity: space in middle of the body for digestion and reproduction, often surrounded by tentacles

Characteristics contd

• Tentacles usually lined with several different types of nematoblasts, which produce structures called nematocysts

• May be mucus coated to entrap prey

• Some have deadly poisons to stun or kill prey

Nematocyst firing

Two Body Forms

Polyp: organisms that are attached with oral surface pointed upward(e.g. corals and sea anemones)

Medusa: free-floating, with oral (mouth and tentacles) surface typically pointed downward (e.g. jellies)

Class: Anthozoa (Corals and Anemones)

• Largest class in the phylum Cnidaria

• Includes more than 6,000 species

• All are polyps

• Some are colonial (corals, soft corals), others are individual (anemones, a few corals) Red Gorgonian,

colonial coral, NOAA

Close up of a coral colony

Coral life cycle

Hard corals and dinoflagellates

• The color of hard corals comes from the dinoflagellates in the genus Symbiodinium, also called zooxanthellae

• These organisms live inside coral, provide food and help eliminate waste through photosynthesis

Zooxanthellae living inside coral

Coral bleaching• Zooxanthellae live best in well-lit,

clear water• Thrive in low-nutrient, less

productive waters (with little plankton to block the sunlight)

• Runoff of pollution can cause plankton to grow and zooxanthellae to die

• Without zooxanthellae, corals lose their colors = coral bleaching

• Global Warming & Bleaching the Reef - YouTube

Class: Hydrozoa (Fire Corals and Siphonophores)

Immortal Jelly

• Alternate between polyp and medusa forms during their life cycle

Ex. Fire corals

• Fire corals—create a mild burn upon contact• Waxy, tan appearance and grow in small tree-like

colonies or as an encrusting colony on an existing reef

• 'The Fire Coral' Pt. 1 - YouTube

Siphonophores• One species measured to be a total

length of 40 m (131 ft)• Many represent a bridge between

colonial animals and complex organisms– Exist as colonies– Within colonies are special polyps

adapted to feeding, reproduction, movement, and other functions

• Major predators with some consuming significant quantities of krill

• Example: Portuguese man-of-war

Portugese Manowar - YouTube

True Jellies

Class: Scyphozoa Class: Cuboza

Class: Scyphozoa (true jellies)

• Range in size from smaller than a coin to more than a meter across with tentacles more than 3 m long

• Most are large planktonic organisms that swim but also drift with the current

• Weak swimmers, move by contracting their rounded body, or bell

• Feed on almost anything they catch

Reproduction

• Scyphozoa life cycle alternates between sessile and freefloating

• Juveniles are polyps, adults are medusas

Scyphozoa continued

• Efficient predators• Prey for Leatherback turtle and several

species of large fish—predators move seasonally with jellies

• Plastic bags, balloons, and small trash often are mistaken by turtles as jellies and can harm them by clogging their digestive systems

Class Cubozoa

• Box Jellyfish are pale blue and transparent and bell or cube shaped with four distinct sides, therefore the name box jellyfish.

• up to 20 cm along each side of the cube or bell

• up to as many as 15 tentacles on each corner which can be 3 metres in length with up to 5,000 nematocysts (stinging cells).

• Box Jellyfish feed on  small fish and crustaceans. 

Cubozoa continued

Cubozoa continued• The box jellyfish has four sets of eyes,

each set at one corner of the animal

Cubozoa continued

• can be found in Australia, the Philippines, Indonesian Coast, Hawaii, Vietnam, the Carribean and other tropical areas

Anemone symbiosis• Found in the tropical Indo-west Pacific or tropical

Pacific, Indian Ocean, and Red Sea• Anemonefish (e.g. clownfish) receive protection

by living amongst the stinging tentacles

• Fish passes back and forth through the tentacles to pick up anemone cells, the anemone recognizes its own cells on the fish so doesn’t sting it

The anemone has not be shown to benefit from this association, therefore the relationship is one of Commensalism

Biology of Cnidarians

• Typically carnivores

• Extracellular/intracellular digestion

• Nerve net

• statocysts