phylum cnidaria

What phylum includes jellyfish, corals, sea anemones, and sea fans?

Phylum Cnidaria.

What are the main learning goals for the Cnidarian lecture?

Know the members of the phylum, their key characteristics, body plans, feeding mechanisms, nematocysts, and the ecological importance of corals.

Where do cnidarians appear on the animal evolutionary tree?

Cnidarians are the next major evolutionary split after sponges.

What does Eumetazoa mean?

"True animals" that possess organized tissues.

What major evolutionary advancement distinguishes cnidarians from sponges?

Cnidarians have true tissues and distinct organ systems.

Are cnidarians diploblastic or triploblastic?

Diploblastic.

What does diploblastic mean?

Having two embryonic tissue layers.

What are the two embryonic tissue layers in cnidarians?

Ectoderm and endoderm, which develop into the epidermis and gastrodermis.

What type of symmetry do cnidarians possess?

Radial symmetry.

What is radial symmetry?

A body plan in which structures are arranged around a central axis.

Why is radial symmetry advantageous for cnidarians?

It allows them to sense and capture prey from all directions.

Are cnidarians predators, herbivores, or detritivores?

Predators.

What type of diet do most cnidarians have?

Carnivorous.

How would you describe the metabolic rate of cnidarians?

Very low metabolic rate.

Why can cnidarians survive in nutrient-poor environments?

Their low metabolic demands require relatively little energy.

Can all cnidarians swim?

No. Some swim while others remain attached to a surface.

What are the four major groups of cnidarians?

Scyphozoans, Hydrozoans, Cubozoans, and Anthozoans.

What are Scyphozoans commonly known as?

True jellyfish.

What are Cubozoans commonly known as?

Box jellyfish.

What are Anthozoans?

Corals and sea anemones.

What are Hydrozoans?

A diverse group containing both marine and freshwater cnidarians.

Which cnidarian group contains the only freshwater species?

Hydrozoans.

What are the two basic body forms found in cnidarians?

Polyp and medusa.

What is a polyp?

A cylindrical, usually sessile body form with tentacles pointing upward.

What is a medusa?

A free-swimming, bell-shaped body form with tentacles hanging downward.

Which cnidarians are primarily polyps?

Anthozoans such as corals and sea anemones.

Which cnidarians are primarily medusae?

Jellyfish.

What structure surrounds the mouth of a cnidarian?

Tentacles.

What is the function of cnidarian tentacles?

Capturing prey, defense, and moving food to the mouth.

How many openings does the digestive tract of a cnidarian have?

One.

What is meant by a "blind gut"?

A digestive system with only one opening that functions as both mouth and anus.

What is the gastrovascular cavity?

The internal cavity responsible for digestion, circulation, and gas exchange.

Why is it called a gastrovascular cavity?

It combines digestive and circulatory functions in one structure.

What are the three major functions of the gastrovascular cavity?

Digestion, circulation, and gas exchange.

Do cnidarians possess a circulatory system?

No.

How are nutrients distributed throughout a cnidarian's body?

Through the gastrovascular cavity and diffusion.

How does gas exchange occur in cnidarians?

By diffusion across body surfaces and within the gastrovascular cavity.

What is diffusion?

The movement of molecules from areas of high concentration to areas of low concentration.

Why can cnidarians rely on diffusion?

Their bodies are relatively thin and simple.

What is the epidermis?

The outer tissue layer of a cnidarian.

What is the gastrodermis?

The inner tissue layer lining the gastrovascular cavity.

What is the mesoglea?

A gelatinous layer located between the epidermis and gastrodermis.

What gives jellyfish their jelly-like appearance?

The mesoglea.

Which tissue layer contains digestive enzymes?

The gastrodermis.

What type of digestion occurs in cnidarians?

Extracellular digestion.

What is extracellular digestion?

The breakdown of food outside cells within the gastrovascular cavity.

How do cnidarians move if they lack complex muscles?

Epithelial cells contain muscle fibers that contract and produce movement.

What are cnidocytes?

Specialized stinging cells unique to cnidarians.

Why are cnidocytes considered a synapomorphy of cnidarians?

Because all cnidarians possess them and they are unique to the phylum.

What is a synapomorphy?

A shared derived characteristic that defines a group.