J.3 Cnidarians

What animals belong to Phylum Cnidaria?

Hydra, jellyfish, Portuguese man-o-war, sea anemones, and coral animals.

What characteristic unites all cnidarians?

Nematocysts (cnidoblasts).

What are nematocysts?

Specialized stinging cells used to capture prey and defense.

How do nematocysts work?

A trigger causes the cell to collapse and shoot out a protein filament containing poison.

What is the function of the nematocyst filament?

Harpoons and immobilizes prey with a chemical anesthetic

What type of digestive system do cnidarians have?

Sac-like digestive system.

What are the two body forms of cnidarians?

Polyp and medusa.

What is a polyp?

A sessile cnidarian body form.

Describe a polyp

Elongated body with a mouth surrounded by tentacles.

What structures are found on polyp tentacles?

Nematocysts

What is a medusa?

A motile cnidarian body form.

What does a medusa resemble?

An inverted polyp.

How does a medusa move?

By changing the shape of its bell.

How many layers make up the body wall of a cnidarian?

Three

What are the three body wall layers?

Ectoderm, mesoglea, and endoderm

What is the innermost body layer?

endoderm

What cavity does the endoderm line?

Gastrovascular cavity (GVC).

What is the function of the endoderm?

Secretes digestive enzymes and absorbs nutrients

What is the outermost body layer?

Ectoderm.

What is the function of the ectoderm?

Protection.

What is mesoglea?

A gel-like middle layer

Is mesoglea a true tissue?

no

What special cells are found in the mesoglea?

Nerve-like cells, contractile cells, and reproductive cells

What is a nerve net?

A network of nerve-like cells without a centralized brain

Do cnidarians have a true brain?

no

Why can't cnidarians be considered cephalized?

They lack concentrated nervous tissue.

How can a sea anemone respond to touch?

Trigger nematocysts, move tentacles toward food, or retract its feeding structures.

What allows cnidarians to respond to their environment?

The combined action of cells in the mesoglea.

Are cnidarians generally hermaphroditic?

many are

What asexual reproduction method is common in Hydra?

budding

What type of fertilization is common among cnidarians?

Broadcast fertilization.

What is the primary body form of hydrozoans?

polyp

Is the hydrozoan body form usually sessile or motile?

sessile

What is a common freshwater hydrozoan?

hydra

How do hydrozoans reproduce asexually?

budding

Are hydrozoans usually solitary or colonial?

Usually solitary, but some are colonial.

Name two colonial hydrozoans.

Obelia and Portuguese man-o-war.

What is the primary body form of scyphozoans?

medusa

What are scyphozoans commonly called?

jellyfish

Are adult jellyfish male or female?

Usually male or female (not hermaphroditic).

: How does fertilization occur in jellyfish?

Gametes are released into the water.

What develops from the fertilized egg?

larva

What happens after the larva stage?

Larva attaches and develops into a polyp.

How are new medusae produced?

Polyps reproduce vegetatively (similar to budding).

What is the primary body form of anthozoans?

polyp

Are anthozoans generally sessile or motile?

sessile

Name examples of anthozoans.

Sea anemones and corals.

Are anthozoans usually polymorphic?

no

Why are coral reefs important?

They support tremendous biodiversity.

Why are coral reefs vulnerable?

They take thousands of years to form but can be damaged quickly.

Why are cnidarians important ecologically?

Coral reefs provide habitat for many species.

Why are cnidarians important medically?

They produce chemicals of pharmaceutical interest.