Cnidariansfrom Modern Latin cnida, from Greek

knide "nettle", from stem of knizein "to

scratch scrape".

Examples● Jellyfish

● Corals

● Sea Anemone

● Hydra

Characteristics● Radial Symmetry

● Stinging Cells (Cnidocyte)

● Two different Body Plans During Life Cycle (exceptions)

● Polyp

● Medusa

Structure and Function● Cnida – Stinging Organelle

● Nematocysts● Spearing Cnida

● Generally on Tentacles

The Sting

• So what would you do if you were stung by a jellyfish?

• Jelly Fish Invasion

Yummy Nematocysts● Leatherback Sea Turtle

Why not use the toxin?

● Nudibranchs – eats cnidocytes and stores the toxin within its body, which turns orange in color… warning to all predators!!

True Jellyfish (Class Scyphozoa)● Predominant life stage

● Medusa

● Generally not strong swimmers

● Photoreceptors

● Box Jellies Closely Related

Hydrozoans● Mostly Colonial

● Specialized Polyps● Feeding Polyp

● Reproductive Polyp

Anthozoans (Flower Animal)● Sea Anemones

● Polyps

● Larger, heavier and more complex than hydra

● Most 1.5 to 10cm in Diameter

● Deep and Shallow Water

● Retracts Tentacles If Disturbed

● Essentially Sessile

Anthopleura elegantissima

Anthozoan Cont. and Gorgonian● Corals

● Hard Corals● Secrete a skeleton of calcium carbonate (Reef Building Coral)

● Large Colonies of Small Polyps

● Gorgonians (Most Common Soft corals)

● Soft Corals● Colonies that look like plants

Nutrition and Digestion● Gastrovascular Cavity

● Digestion and movement of materials within animal

● Waste if forced back out of the mouth after digestion (Yum!)

Reproduction● Asexually

● Generally during polyp state resulting in more polyps

● Sexually

● Generally in the medusa stage

Life Cycle

Ecological Relationships● Predator-Prey

● Predator to many species (stinging cells)

● Prey to sea turtles, some fish and molluscs● Crown-of thorns sea star

feeds on coral

● Habitat Formation

● Coral reefs provide a solid surface

Ecological Relationships● Symbiotic Relationships

● Portuguese man-of-war and man-of-war fish

● Coral and zooxanthellae

● Hermit crab and anemone (Eupagurusprideauxi and Aamsiapalliata)