CnidariansCnidarians

““The guys with the stinging The guys with the stinging tentaclestentacles””

All About Cnidarians

• Evolution of multicellular animals with tissues that perform special functions

• Cnidarians: Stinging animals

• Mostly marine

• 10,000 known species

• 2 body forms: medusa and polyp

AnatomyA. Polymorphism- Cnidarians have

more than one body form:1. Polyp

2. Medusa

• The life history of some cnidarians includes both polyp and medusa stages. Others spend their entire lives as either polyp or medusa

medusa

• Free floating form which is transported by water currents, mouth with surrounding tentacles are positioned downward

Medusa • Umbrella shape

• Tentacles around mouth

• Motile, Free-swimming

polyp

• Sessile, attached form with mouth and tentacles positioned upward

Polyp Form• Tube with tentacles

around the mouth

• Sessile

Coral polyp

Polyp (sea anemone)

Polyp (Hydra)

CnidariansCnidarians actually exhibit radial symmetry in which similar body parts can be grouped around a central axis.

•Here we also observe a large jump on the evolutionary scale: tissues that perform specific functions.

• Animals with radial symmetry look the same from all sides and have no head, front, or back.

• They do, however, have an oral surface, where the mouth is, and an aboral surface on the opposite side

• See figure 7.6 page 119

Radial Symmetry

Compass jellyfish

RadialRadial

tissues

• Two layers present• Epidermis covers body surface (external)• Gastrodermis lines internal body cavity and is

specialized for digestion• There is also a narrow, gelatinous middle

layer, mesoglea,that usually doesn’t contain cells. Forms “bell” of medusae

Two Tissue Layers

1. EPIDERMIS – OUTER LAYER2. GASTRODERMIS – STOMACH CAVITY

MESOGLEA – JELLY MATERIAL BETWEEN TISSUE LAYERS ABUNDANT IN JELLYFISH TO HELP THEM FLOAT

Cnidocytes

• Stinging cells

• Nematocyst capsules located on tentacles

• These are used for protection and feeding

Cnidocytes-Stinging Cells• Within the cnidocyte is the

nematocyst (which is like a capsule)

• The capsule has the stinging structure which is a hollow

thread (Filament) with barbs• Most contain a toxin• Very small, but discharged in large

numbers• Usually the sting is only strong

enough to kill zooplankton or tiny fish

• But there are exceptions!

• Discharged nematocysts, Discharged nematocysts, stinging cells used for stinging cells used for

defense and defense and prey prey capturecapture, have been the , have been the plague of more than fish.plague of more than fish.

• Stings from certain Stings from certain

jellyfish have resulted in jellyfish have resulted in death in a matter of death in a matter of hours, especially for hours, especially for infants.infants.

Discharging nematocyst

• http://www.youtube.com/watch?v=6zJiBc_N1Zk

Jellyfish stings

• http://www.youtube.com/watch?v=-Tp38DUjUnM

• 1:01

• http://www.youtube.com/watch?v=SP6TB8kiZB0

Digestive and nervous systems

• Digestive system is incomplete (sac-like with mouth only)

• Centrally located mouth surrounded by tentacles

• Tentacles capture and handle food

• Mouth opens into gut where food is digested

• Nerve net throughout body coordinates movements

• Some jellyfish also have sensory cells and contractile cells

One Opening System

Food enters through the mouth and is digested in the cells.Wastes are excreted through the mouth.

WASTES, GAMETES

OUT

Sperm and eggs are released through the mouth.

FOOD IN

Response• No nervous system

• No brain

• Nerve net around mouth

• Nerves cover the body but do not tell the difference between body parts.

Respiration

• Via diffusion

• Body is two cell layers thick

HabitatAquatic:

• Most are Marine

• A few are freshwater

Feeding1. Carnivores

(predators)

2. Process of feeding

a. Tentacles sting prey with

nematocysts

b. Tentacles grab prey

c. Prey pulled into mouth

3. Prey moved into gastro-vascular cavity (GVC)*

4. GVC makes enzymes, breaks down food, extra-cellular digestion

5. Undigested food moves back out of mouth

Lion’s mane eats another jelly!

Process of feeding

3. Prey stuffed into gastro-vascular cavity (GVC)*

4. GVC makes enzymes, extra-cellular digestion

5. Undigested food back out mouth

**incomplete digestive tract (no incomplete digestive tract (no anus)anus)

Locomotion

A. Medusa- motile, free-swimming

B. Polyps- sessile, attached to hard substrate

Exceptions:

1. Hydra tumbles on tentacles

2. Sea anemones glide on pedal disc

Reproduction

1. Asexual budding2. Sexual

a. Medusae release sperm & eggs b. Larvae are free-swimming

Sexual reproduction

• Medusa is normally the sexual stage with epidermal gonads. Eggs and sperm released from medusa

• Zygote develops into swimming larva called a planula

• Planula settles on bottom to form colony

• Eventually, new medusa are formed

Planula

Life Cycle of a Typical Cnidarian

• Alternation of Generations• One form is the polyp (a cylinder with

the closed end attached to the substrate and the open end with the mouth and tentacles directed upward)

• The other form is the medusa, free-swimming, with the mouth underneath (like a jellyfish)

Life Cycle of a Typical Cnidarian

Alternation of Generations

Hermaphrodite

sexual

asexual

Cnidarian life cycle

• http://www.youtube.com/watch?v=ct9KyLmnu0I

• http://www.youtube.com/watch?v=K9cFbJ8qYWg

Phylum CnidariaThe Classes of Cnidaria are:

• Anthozoa- Sea Anemones and Corals

• Hydrozoa- Hydra

• Scyphozoa- “true” jellyfish

• Cubozoa- “box-shaped” jellyfish

• Ctenophora- non stinging Cnidarians: Comb Jellies (covering separately)

Class Anthozoa

• All marine “flower animal”• Corals, anemones, sea fans/whips, sea pansy• Colonial polyps that normally lack a medusa stage• Sting organisms around them• Can move by crawling along the substrate• Corals secrete calcium carbonate “shells”• Most coral species possess symbiotic algae within

body tissues called zooxanthellae

Anthozoa- sea fan

Anthozoa- anemone

Sea anemone

Giant Sea Anemone

Anthozoa- coral

Sun Coral

Brain Coral

Anemone Video

• http://www.youtube.com/watch?v=NFO4DwEkkr0

Homework

• Research the relationship between clown fish and anemones

• http://video.nationalgeographic.com/video/animals/invertebrates-animals/other-invertebrates/clownfish_amonganemones/

Class Scyphozoa

• True jellyfish. All marine

• Free swimming large medusa forms with polyp only in reproductive life

• They move by rhythmic contractions of the bell, but cannot fight against prevailing water currents

• Many with powerful stings

Scyphozoa

National geographic jellyfish

• Dance of the jellyfish

• http://video.nationalgeographic.com/video/animals/invertebrates-animals/other-invertebrates/dance-jellyfish-eorg/

• 1 minute

National geographic

• http://video.nationalgeographic.com/video/animals/invertebrates-animals/other-invertebrates/jellyfish/

Super Jellies

• http://www.youtube.com/watch?v=NbpB5F9CcLc

• 3:31

Jellyfish video

• http://www.youtube.com/watch?v=B3faXiTZdjo

• 3:43

• http://www.youtube.com/watch?v=pimIbTqJLZc

• 11:08

Homework

• The case of the killer Cnidarians page 122

• Research most deadly jellyfish

• Irukandji

• Carukia barnesi

Killer Jellyfish

• http://www.youtube.com/watch?v=GK_Cl_54Qh8

• http://www.youtube.com/watch?v=Ml7bO021DMk

• http://www.youtube.com/watch?v=rQ2WYbJSvTk

worksheet

• “Killer Cnidarians” (Hoyle)

Life cycle of Scyphozoa

Largest known jellyfish

• Lion’s Mane Jelly

• bell of a lion's mane jellyfish can be over 8 feet across

• tentacles can reach over 100 feet, and they have many of them - the lion's mane jellyfish has eight groups of tentacles, and there are 70-150 tentacles in each group

Lion’s Mane Jellyfish

• Encountering a lion's mane jellyfish probably won't be lethal, but it won't be fun, either. A lion's mane jellyfish sting usually results in pain and redness in the area of the sting. The sticky tentacles of a lion's mane jellyfish can sting even when the jellyfish is dead, so give lion's mane jellyfish on the beach a wide berth. In 2010, a lion's mane jellyfish washed ashore in Rye, NH, where it stung 50-100 unsuspecting bathers

Class Hydrozoa

• Mostly polyp forms with reproductive medusa

• Freshwater and marine

• Physalia

• Portuguese man of war

• hydra

Hydrozoa

Hydra

• Exist only as polyps

Portuguese man of war

National geographic portuguese man of war

• http://animals.nationalgeographic.com/animals/invertebrates/portuguese-man-of-war/

National geographic port. Man of war

• http://www.youtube.com/watch?v=RBdCpcapB0s

Ecological RoleA. Predators and prey

B. Neurotoxins in medical research

C. Coral – jewelry, building, reefs (surfing!)

D. Coral reefs - habitat for many different species, great biodiversity, protect coastline

E. Symbiosis with other organisms

Cnidarians Documentary

• http://www.youtube.com/watch?v=AjM-WOeM3uA

• 9:17