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

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

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

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

nematocysts

 loaded Discharged 

 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

 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

 Cnidarians do not have a BRAIN, but do have nerve nets throughout the body.  The NERVE NET is concentrated around the mouth.

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

Sensory Receptors  Simple sensory organs surround the medusa bell  1. statocysts are used for balance  2. Ocelli (eye spots) detect light Statocysts 

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

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

Asexual Reproduction  Polyps produce new polyps or medusae by budding

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

Hydras- a Hydrozoan  Spend most of life as polyp  Can move with a somersaulting movement

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

Jellyfish  Most of life is as a medusa

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

Sea Anemones + Coral  Only have the polyp stage  Most ecologically important invertebrates  Sea anemones are solitary polyps

Sea anemones

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

Corals  Grow in shallow, tropical water  Produce skeletons of CaCO 3  Most are colonial, creating coral reefs  Entire ecosystems revolve around coral reefs

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

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