Phylum Cnidaria

Jellyfish, Coral, Sea Anemone, and Hydroids

Cnidarians• Stinging cell animals

• Also Known As: Coelenterates: “Hollow Gut”

• Radial Symmetry: similar body parts surrounding a central axis

Body Plan

• No segments: oral and aboral sides• Hydrostatic Skeleton: fill body cavity with water

to remain upright.• Shrink down as defense• Organized at tissue level. (No true organs)• Epidermis: outer cells (ectoderm)• Gastrodermis: lines stomach (endoderm)• Mesoglea: middle layer of gelatinous material; can

be thick or thin.

Digestion

• Food is digested in the sac-like digestive cavity (only one opening)

• Extracellular and intracellular digestion

• Extracellular: outside of cells

• Intracellular: inside of cells

• Waste is expelled out of the mouth

Unique Features

• Cnidoblasts: stinging cells• Inside each cell is a nematocyst, coiled thread with

barb at the end.• The nematocyst can be discharged by either

physical or chemical stimulus.• Physical- cnidocil (modified flagella) acts as a

trigger• Contain a poisonous neurotoxin, varies by species

Cnidoblast

Nematocyst

Nervous System• Nerve cells interconnect to form a nerve net

Life Cycle

• Jellyfish have separate sexes• Both sexual and asexual reproduction• Sexual: external or internal (depending on

species), sperm and egg form a zygote which grows into a swimming larva called the planula.

• In some cases the planula attaches to a hard substrate and develops into a polyp.

Life Cycle cont.

• The polyp resembles an upside-down jellyfish medusa.

• Small umbrella like medusas break off from the polyp by budding (asexual)

Classification of Cnidarians

• Class Hydrozoa- Hydra, Physalia, and Obelia

• Class Scyphozoa- True Jellyfish

• Class Cubozoa- box jellyfish

• Class Anthozoa- Corals and Sea Anemones

Class Hydrozoa

• Usually colonial, except Hydra

• Composition of colonies- 3 types

1. Gastrozoid- responsible for feeding

2. Gonozoids- responsible for sexual reproduction

3. Dactyliozoids- responsible for defense; have numerous nematocysts.

Class Scyphozoa

• All marine; medusa is dominant life cycle• Mesoglea is a large part of the body (mostly

dead matter)• Gastroderm have nematocysts; food may be

eaten alive• More toxic than hydrozoans• Well developed sensory organs and glands

- eyespot and chemoreceptors

Class Cubozoa

• Cube-like jellyfish

• Have four flattened, blade-like structures called pedalia

• Complex eyes with lenses and retinas (no brain though)

• Only 16 species: Irukandji and Chironex- deadly box jellyfish. Can kill a human in minutes.

Irukandji: Carukia barnes

• One of, if not the deadliest box jellfish.

• 2.5 cm (1 inch) in diameter

Box Jellyfish Sting

Chironex- Sea Wasp

Class Anthozoa

• No medusa stage in life cycle

• Polyps produce eggs and sperm that develop into planula larva

• Solitary: sea anemone

• Colonial: coral

Tube Sea Anemone

Sea Anemone

Soft Coral

Corals and Coral Reefs

• Corals are colonial cnidarians• Dominant form is the polyp• Coral reef is a massive structure composed

of calcium carbonate built by coral polyps and the organisms that live with in them

• The polyps take up calcium in the sea water and zooxanthellae, which live inside the polyp, take up CO2, which make limestone

Zooxanthellae

Hard Coral

Coral Reefs

• Found only in tropical areas

• Warm and clear water

• Shallow water- zooxanthellae require sunlight to photosynthesize

• Zooxanthellae are the primary producers of the coral reef

Coral Reef Formation

• Fringing Reef: occurs when a seamount pierces the sea surface to form an island and provides a base on which the coral can grow

• Barrier Reef: occurs if a seamount subsides slowly enough and the coral continues to grow upward at a rate that is not exceeded by the rising water. A lagoon is formed.

• Atoll- occurs if the seamount disappears below the surface and the coral reef is left as a ring.

Atafu Atoll: South Pacific

Symbiosis and Cnidarians

• Symbiosis: literally means to live together

1. Mutualism: both organisms benefit from living together

2. Commensalism: one organism benefits, the other is unaffected

3. Parasitism: one organism benefits, one is harmed.

Clownfish and Anemones

Sea Anemones and Clownfish

• Usually, fish the size of clownfish are stung and eaten by an anemone

• Clownfish become immune to the anemones nematocysts because of a mucus coating

• The mucus inhibits the anemone’s sting• The anemone provides protection and scraps of food

for the clownfish• The clownfish lures prey into the anemone and

cleans the anemone• What kind of relationship is this?______________

Coral and Zooxanthellae

Corals and Zooxanthellae

• Zooxanthellae are dinoflagellates that are taken up by the coral polyps.

• Zooxanthellae contain chloroplasts• Coral use the glucose made by the zooxanthellae

as an energy supplement• The zooxanthellae benefit because they are

protected and receive nutrients from the coral polyp.

• What type of relationship is this? _____________

Phylum Ctenophora

Comb Jellies

Take notes on your own sheet of paper, only write down what is

underlined.

Ctenophora

Ctenophora

• Group of 100 species• Oval shaped with radial symmetry• Resemble cnidarians but are NOT!• Swim with 8 rows of ciliary combs (long cilia

fused at the base)• Cilia refract light which

cause a rainbow effect.• Body length varies from a few centimeters to 2

m long.

Habitat• Exclusively marine

• Can be found in cold or warm water

Diet

• Carnivores

• Consume fish larvae and plankton

• Can expand stomach to eat organisms twice their size.

• Capture prey with two long tentacles armed with sticky cells called colloblasts

• A few species have nematocysts

Reproduction

• Sexual reproduction

• Hermaphrodites

• No polyp form; only medusa

Life Cycle

Deep Sea Comb Jelly

On a sheet of paper do the following

1) Title the paper: Porifera, Cnidaria, and Ctenophora Lab

2)Number your paper from 1-22

3)Leave space on #11, #14 and #16 for drawings (about 5 lines)

4)Use your Porifera Notes and Cnidaria Notes to answer the questions (answers only, don’t worry about writing the questions)