Corals, Anemones, Sea Fans, and Jellyfish Aquatic Stinging Nettles
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Chapter 6 Pages 6-7 to 6-8
Corals, Anemones, Sea Fans, and Jellyfish
Characteristics of Phylum Cnidaria
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Members of Phylum Cnidaria
• Phylum Cnidaria includes soft and hard
corals, sea anemones, hydroids, sea fans, jelly
fish, and siphonophores.
Characteristics of Phylum Cnidaria
•
Anatomical characteristics include:
– They are radially symmetrical – symmetry
around a central point.
– They have a cup (polyp) or
umbrella-shaped (medusa) body
made of two layers of cells.
Polyp - Attached
Anemones and Corals
Medusa - Free-Floating
Jellyfish
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Characteristics of Phylum Cnidaria
• Anatomical characteristics include:
– Polyps can be solitary or colonial; medusa are freefloating
– Mesoglea (jelly-like) separates the
two tissue layers.
– Tentacles line the rim of the polyp
and medusa with a mouth-like
opening in the middle.
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Characteristics of Phylum Cnidaria
• Anatomical characteristics include:
– They have a mouth that opens into the gastrovascular cavity (a space in the middle of their
body used for digestion/reproduction).
– They are structurally uncomplicated, with
simple nerve net, muscle cells,
and light receptors.
– All share the ability to defend
themselves with nematocysts.
• These stinging structures
are composed of special cells
called cnidocytes.
(You’ve seen better in video…)
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Special Attributes of Coral and Anemones
• The largest class in phylum Cnidaria is class Anthozoa, the
corals and anemones. Over 6,000 species.
– Members of this class are polyps that
attach to the reef or other substrate.
– Most coral and soft coral are colonial,
anemones are individual organisms.
Soft Coral
Elkhorn Coral
Stalked Anemone
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• Hard coral are the most ecologically significant thanks
to the massive calcium carbonate reefs they build.
– Coral colonies can grow for centuries and become so
large that they shape coastlines and build entire
islands.
– Zooxanthellae live in the tissues of most species of
hard coral, providing it food and helping eliminate
waste through photosynthesis. Supercharged….
Plate Coral
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Special Attributes of Coral and Anemones
• Zooxanthellae corals:
– Live best in well-lit, clear water.
– Actually thrive in low-nutrient, less productive areas.
– Are sensitive to runoffs, fertilizers, etc. (can kill them)
– Become colorless when stressed.
This is called coral bleaching – a sign of a diseased
and dying colony.
Coral Bleaching
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• Soft coral and sea fans grow into tree-like structures
built on protein skeletons. They are not reef builders.
• Anemones have a mutualistic relationship with
various species of anemonefish.
– The fish receive protection by living in the anemone
and the anemone receives food from the fish.
Diver and Sea Fan
Soft Coral
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Special Attributes of Jellyfish
• Jellyfish:
– Are members of class Scyphozoa.
– Range in size from smaller than a coin to more than 1
meter (3.28 feet) across with tentacles more than 3
meters (9.8 feet) long.
– Are large planktonic organisms that swim, but also
drift with the current.
– Are weak swimmers that
move by contracting and
pulsating their rounded
body, or bell.
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• Jellyfish:
– Feed on almost anything they catch with their tentacles.
– Some species have very short tentacles and very mild stings,
making them more of an annoyance than a threat to
swimmers. Others have long tentacles and can sting
severely.
– Are eaten by some species of fish & turtles
– Box jellyfish have a very potent
Box Jellyfish
toxin and can kill several
adult humans.
Box Jellyfish
Stings
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Special Attributes of Fire Corals and Siphonophores
• Fire coral:
– Belong in the class Hydrozoa.
– Colonial organism, looking much like hard corals.
– Different from hard corals - forming
more complex colonies and having
complex lifecycles.
Tentacles with Nematocysts
– Life cycle alternates between
polyp and medusa.
– Most species can sting humans stings can be serious, hence
their name.
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• Siphonophores:
– Belong in the class Hydrozoa.
– Exist as planktonic colonies, yet within the colonies are specialized
polyps adapted to feeding, reproduction, movement and other
functions.
– Can exceed 40 meters (131 feet) in length.
– Can have powerful stings.
– Are major predators.
– Are a bridge between colonial animals and complex organisms.
Diver with Planktonic
Siphonophore
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Special Attributes of Fire Corals
and Siphonophores
• The Portuguese Man-of-War is a
siphonophore with a specialized
buoyancy chamber to help it
remain at the surface and
tentacles underwater to catch
prey.
Float
Tentacles with stinging,
feeding, reproductive
polyps
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Comb Jellies - Gelatinous Carnivores
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Comb Jellies - Gelatinous Carnivores
• Characteristics of Phylum Ctenophora
– Differences with jellyfish:
• Ctenophores lack bag-like cnidarian body shape and
stinging cells.
– All are marine, living in many environments.
– Have “comb rows” of cilia on
bodies for movement.
– Most are small - only a few
millimeters or centimeters long.
– Nearly colorless.
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Comb Jellies - Gelatinous Carnivores
• Characteristics of Phylum Ctenophora
– Exhibit rainbow colored light produced by
cilia.
– Have organized tissues but lack true organs.
– Has a nerve net and reproduces sexually.
– Are carnivorous - eating small plankton.
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