Name:

Phylum Cnidaria: Jellies, Anemones and Corals

Learning Objectives: *Refer to Kingdom Animalia Unit Plan

Text page: 371 *This is required reading.

What are some common cnidarians?

Cnidarian Common Characteristics

Despite the diversity in cnidarian form, all members of this phylum share the following characteristics:

1

a) Level of Organization

Cnidaria are one level more complex than Porifera as they have tissues, making them eumetazoans.

b) Body Plan

Cnidarians have a sac-like body plan with two tissue layers (endoderm and ectoderm) surrounding a

central gastrovascular cavity (gvc).

-Instead of a mesoderm, cnidarians have a mesoglea,

a gel-like layer between the endo and ectoderm. This

is not considered a germ layer!

What are some functions for the gvc in Cnidarians?

Gastro: Digestive enzymes secreted from

gastrodermis break down nutrients in the gvc.

Nutrients are absorbed by the gastrodermis cells.

-Vascular: O2 diffuses from the water in the gvc into

the gastrodermis cells. CO2 diffuses into the gvc.

-Hydrostatic skeleton: Muscles contract against the H2O in the gvc to allow movement.

c) Symmetry

What type of symmetry do cnidarians

have? Radial

2

Compare and contrast the two different Cnidarian body forms below:

Polyp Medusa

Movement Sessile Free Floating

Reproduction Asexual Stage (budding) Sexual Stage

Other

d) Tissues and Cell Specialization

Cnidarians have many cells and tissues specialized for particular functions.

i) All cnidarians have stinging cells called cnidocytes that are used for defense and paralyzing prey.

*Watch How Does a Jellyfish Sting from TED-Ed at https://goo.gl/GJsHXW

3

ii) Epitheliomuscular Cells: Contract to allow cnidarians to bend and move.

iii) Sensory Cells: Chemical and touch sensitive. Linked to a nerve net (1st nervous system!)

iv) Interstitial Cells: Are similar to stem cells in that they can replace any other type of cell.

v) Gland Cells: Secrete enzymes into the gvc for digestion.

vi) Nutritive Muscular Cells: Absorb digestive nutrients and also contract for movement.

Cnidarian Essential Functions

a) Digestion

Digestion occurs in the GVC,

where digestive enzymes

breakdown food particles into

small enough molecules to be

engulfed by or diffuse through

the cell membrane of nutritive

muscular cells.

ii) Cellular Respiration

Gases diffuse from high concentration from low concentrations (O2 into cells from H2O; CO2 from cells

into H2O).

4

iii) Reproduction

Some Cnidarians pass sequentially through a polyp and medusa stage in their life cycle, such as the

Obelia life cycle below.

*Watch a budding polyp release Ephyra at https://goo.gl/Kpb1nJ

Why Do We Care about Cnidarians?

Conduct your own research to discover at least five ways that corals are important to their ecosystems and

the larger world

1. Used in scientific research to discover more about the evolution of animals (what we are doing!)

2 and 3. Corals provide habitat for many organisms and protection against erosion.

5

4. Medusa can be food for other organisms.

5. Medical uses.

Threats to Cnidarians

The Cnidarian currently

experiencing the greatest threat

to its existence is coral as a

result of rising ocean

temperatures and pollution.

*Watch Coral Bleaching

HHMI Biointeractive

Animation at https://goo.gl/GMZcvE

Corals are polyp cnidarians

that produce skeletons of calcium carbonate and live in groups of genetically identical individuals

(asexual reproduction).

Corals catch small fish using cnidocytes, but most of their energy comes from symbiotic algae

(photosynthesis). These algae leave coral tissues during bleaching events, depriving the coral of its main

There are three general methods for working to bring back damaged coral reefs:

*Watch Conserving our Spectacular, Vulnerable Coral Reefs from TED-Ed at https://goo.gl/E3518Y

1. Structural Restoration:

Construction of artificial reefs to

increase surface area available for coral

growth.

Required in areas where structural

integrity of ecosystem has been

compromised or lost due to disturbances

(dynamite fishing, landslides…).

6

2. Biological Restoration:

Increasing the number of corals living in a suitable habitat by

collecting/rehabilitating naturally broken coral fragments,

culturing coral larvae and transplanting living coral colonies.

Necessary in areas where coral die off has occurred

(bleaching, disease, predation, ect).

3. Physical Restoration:

Improve the health and growth of reefs by adding coral

nurseries, changing water chemistry through electrolysis….

7