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 CaCO3

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