KINGDOM ANIMALIAPhylum Cnidaria

Phylum Cnidaria

The phylum name comes from Cnidaria, the Greek word for nettle, a plant that has stinging hairs.

Members of the Phylum Cnidaria

…exhibit radial or biradialsymmetry.…are all aquatic (typically marine, but some freshwater).…are sessile, free-floating, or weak swimming.…have a tissue-level organization.…have a primitive nervous system.…have stinging cells.

Question

Which of the following characteristics sets the members of the phylum Cnidaria apart from all other animals?

A. They are all aquatic.

B. They have stinging cells.

C. They are all multicellular.

D. They are sessile as adults.

General Organization

Cnidarian bodies are organized around the gastrovascular cavity, where digestion takes place.Two layers of cells: gastrodermis (lining the digestive tract) and epidermis (outer layer)Mesoglea: jelly substance in between the two cell layers.

Question

In a cnidarian, the jelly substance in between the two cell layers is called

A. mesoglea

B. cnidoglea

C. epidermis

D. gastrodermis

Reproduction

Sexual reproduction: gametes are shed directly into the water.

Asexual reproduction: usually by budding, some by fission.

Question

Cnidarians reproduce in all of the following ways, EXCEPT

A. Asexual fission

B. Asexual budding

C. Sexual regeneration

D. Sexual reproduction involving egg and sperm

Life Cycles:Polyp and Medusa

Cnidarians generally alternate between sessile polyps that reproduce asexually and swimming medusae that reproduce sexually.

One of these stages is missing in many forms.

Question

True or False:

This picture represents the medusa body plan of a cnidarian.

Stinging Tentacles

The tentacles of all cnidarians produce nematocysts, organelles that can discharge threads to entangle, penetrate, or poison prey.

The tentacles are composed of cells called cnidocytes, which contain the nematocysts.

Cnidocyte

Question

In a cnidarian, the cnidocytesare used forA. swimming

B. digesting food

C. paralyzing prey

D. sensing predators

Feeding and Digestion

Cnidarians prey on a variety of appropriate-sized prey.

Prey is normally drawn into the gastrovascular cavity by the tentacles.

Here, gland cells discharge enzymes onto the food.

Question

Where does digestion take place for cnidarians?

A. In the tentacles

B. In the epidermis

C. Outside the body

D. In the gastrovascular cavity

Four Important Cnidarian Classes

1. Class Hydrozoa

Mostly marine

Alteration of generation (polyp and medusa stages) is usually exhibited

Includes hydroids, fire corals, and Portugese man-of-war

Hydrozoan: Hydra

Portuguese Man of War

Four Important Cnidarian Classes

2. Class Scyphozoa

Dominant stage is the medusa

Polyp is absent or reduced

Cup-shaped umbrellas

Includes true jellyfish

Scyphozoa: Aurelia labiata

Four Important Cnidarian Classes

3. Class Cubozoa

Like jellyfishes, but they have cubical umbrellas.

Some may deliver fatal stings.

Includes the box jelly, one of the 10 most venomous organisms on earth.

Cubozoans

Four Important Cnidarian Classes

4. Class Anthozoa

Polyps with a flowerlike appearance

No medusa stage

All marine, found all over the world

Includes sea anemones, corals, sea fans, and sea whips.

Anthozoans: Corals

Anthozoans: Anemones

Economic ImportanceReef-building corals provide habitat for fish and other animals that are important as food sources for humans.Coral reefs are tourist attractions and coral rocks are used as building materials and jewelry.