Cnidarians

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Cnidarians

• Jellyfish, Hydra, Corals, Sea Anemones,
• Sea Fans and Sea Pens

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Cnidarians

• Soft-bodied animals
• Stinging tentacles
• Sac Body Plan
• Tissue Level of Organization
• Radial Symmetry

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• Two basic body forms
• Medusa (bell- shaped) and
• Polyp (flower-like)

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Structure

• Mouth both entry of food and exit of wastes
• Tentacles contain spring-loaded nematocysts to
  sting and immobilize their prey
• Tentacles guide paralyzed food into the mouth
• Gastrovascular cavity food is digested here

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nematocysts
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?loaded
Discharged ?
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• Many cnidarians do not have to eat due to
  symbiotic relationships with autotrophic protists
• The protists live in the gastroderm of the animal
• Some cnidarians are so dependent on the
  relationship that they will die if not kept in
  bright sunlight

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• Some cnidarians have long, tube-shaped branching
  gastrovascular cavities
• They do not need to send wastes back through the
  mouth wastes simply diffuse out through the cell
  walls of the epidermis

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• Cnidarians sense their environments using chemo
  and touch receptors in the epidermal layer

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Sensory Receptors

• Simple sensory organs surround the medusa bell
• 1. statocysts are used for balance
• 2. Ocelli (eye spots) detect light

Statocysts ?
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• Cnidarians lack true muscle cells, but have cells
  that change shape when stimulated by the nerve
  net therefore, they can move.

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• The medusa can open and close like an umbrella,
  allowing it to move by jet propulsion when
  water is forced out of the medusa

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Asexual Reproduction

• Polyps produce new polyps or medusae by budding

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Sexual Reproduction

• Mature medusa release gametes into the water
• After fertilization, the zygote becomes a
  ciliated larvae that swims around
• Eventually, the larva attaches to a hard surface
  and grows into a polyp

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Hydras- a Hydrozoan

• Spend most of life as polyp
• Can move with a somersaulting movement

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Portuguese Man-Of-War

• A type of hydrozoan that grows in a colony
• One of the polyps becomes a float to keep the
  colony on the surface
• They may produce very long tentacles the poison
  in the nematocysts is very strong and causes
  humans great pain

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Jellyfish

• Most of life is as a medusa

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Box jelly ?

• The sting of most jelly fish are harmless to
  humans, but the tiny, Australian jellyfish can
  kill you in 3-20 minutes.

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Sea Anemones Coral

• Only have the polyp stage
• Most ecologically important invertebrates
• Sea anemones are solitary polyps

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Sea anemones
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Clownfish and Sea Anemone symbiotic
relationship tentacles protect clown fish from
predators, clownfish protects tentacles from
being eaten
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Corals

• Grow in shallow, tropical water
• Produce skeletons of CaCO3
• Most are colonial, creating coral reefs
• Entire ecosystems revolve around coral reefs

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• Coral reefs also protect the land from the ocean
  swells and waves

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• Corals produce chemicals to prevent being
  overgrown by other organisms. Some of these
  chemicals have been used as anti-cancer
  medications