Phylum Cnidaria or Coelenterata

Cnidaria

� Definition: � Cnidaria: Stinging Cells

� Cnid = nettled, aira = plural� Nettled = covered with stinging hairs

� Coelenterata: Hollow-gut

� Common Example: � Jellyfish� Sea anemone � Coral

Characteristics

A. Body plan is sac-likeB. Internal body cavityC. Extracellular digestion in the

gastrovascular cavitygastrovascular cavityD. Biradial SymmetryE. Extensions from the body. Tentacles

used for � food capturing � defense

Characteristics Cont…

F. Sense organs appear first then radiates as ocelli (light sensitive)

G. LocomotionLocomotion� Muscular contractions� Free floating� Summersaults

H. True Nerve cells for a Central Nervous System

Classes Hydrozoa

Greek Meaning Water Serpent• hydra = water and • zoan= animal

• Solitary animal• Solitary animal• Colonial meaning found in groups• Fresh and Marine water• Example: Brown Hydra, Green Hydra,

Obelia

Green Hydra

Brown Hydra

Obelia

Scyphazoa

� Greek Meaning Skyphos = cup and zoan = animal

� Solitary only in the polyp stage� Solitary only in the polyp stage� Bell shape body� Mesoglea layer� Medusa (tentacles extend down)

Class Scyphozoa

� Examples� Jellyfish, � Aurelia� Aurelia� By the Wind

Sailor

Jellyfish

Aurelia

By the Wind Sailor

By the Wind Sailor

Class Anthozoa

� Greek Meaning � Anthos = flower � Zoan = animal� Zoan = animal

� All polyps� No Medusa� Solitary or Colonial� Sessile

Anthozoa

� Examples� Sea anemone� Coral� Coral

� Polyps are attached or sessile

Class Notes

sessile

� stalk-like structure

Class Notes

� Medusa are free floating and muscle muscle contractions

� Bell-shaped body

Class Notes

� Entirely Aquatic

� No excretory system or respiratory systemsystem

� Exoskeleton made of chiton or lime

Class Notes

� Food and Defense

� Cnidocytes (stinging cells)� Single cell

� Flagella like structure with barbs = nematocysts

Cnidocytes

� When the hair-like trigger is activated, the shaft of the cnidocyst penetrates the target organism, and the hollow thread is everted into it

� Takes no more than a few µs,

Cnidocyte Action

� Takes no more than a few µs, and is able to reach about 40,000g

� Recent research suggests the process to occur as fast as 700 nanoseconds

� After penetration, the neurotoxin content of the nematocyst is injected into the target organism immediately paralyzes the mobile prey, thus allowing the sessile cnidarian to devour it

Portuguese Man of War

� Not a true Jellyfish� Order of the class Hydrozoa –

SiphonophoraeSiphonophorae� Appears to be a single organism, but is

a colony of cells

Portugese Man of War

Terms��PolypPolyp

��MedusaMedusa

��NematocystsNematocysts

��Gastrovascular CavityGastrovascular Cavity

��MesogleaMesoglea

��CnidocytesCnidocytes

��TentaclesTentacles

What class do hydra belong to?

What Phylum do Jellies belong to?

Jellyfish Attack

What Phylum does Coral belong to?

What are the stinging cells called?