Corals, Anemones, Sea Fans, and Jellyfish -Aquatic Stinging Nettles

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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) orumbrella-shaped (medusa) bodymade of two layers of cells.

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Polyp - AttachedAnemones and Corals

Medusa - Free-FloatingJellyfish

Characteristics of Phylum Cnidaria• Anatomical characteristics include:

– Polyps can be solitary or colonial; medusa are free-floating

– Mesoglea (jelly-like) separates thetwo tissue layers.

– Tentacles line the rim of the polypand medusa with a mouth-likeopening in the middle.

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Characteristics of Phylum Cnidaria• Anatomical characteristics include:

– They have a mouth that opens into the gastro-vascular 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 defendthemselves with nematocysts.• These stinging structures

are composed of special cellscalled 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.

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Stalked AnemoneElkhorn CoralSoft Coral

• 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….

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Plate Coral

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.

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Coral Bleaching

• 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.

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Diver and Sea Fan

Soft Coral

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 thatmove by contracting andpulsating their roundedbody, 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

toxin and can kill several adult humans.

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Box Jellyfish

Box JellyfishStings

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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 havingcomplex lifecycles.

– Life cycle alternates betweenpolyp and medusa.

– Most species can sting humans -stings can be serious, hencetheir name.

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Tentacles with Nematocysts

• 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.

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Diver with Planktonic Siphonophore

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.

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Float

Tentacles with stinging, feeding, reproductive polyps

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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