Download Phylum Cnidaria Cnidarians - Soft bodied animals with stinging cells

Phylum Cnidaria
Cnidarians
Soft bodied animals with stinging cells on tentacles around the mouth
Can live as individuals or in colonies
Aquatic (fresh and marine)
Sessile or motile (jellyfish, sea anemones)
Some specialized tissue
Specialized cells
Body plan
have two plans
1.
Polyp
o mostly sessile
o has a long body tube with a mouth and tentacles at one end
o ex) sea anemones
2.
Medusa
o motile
o generally dome shaped with a mouth and tentacles in the underside
(ventral)
o ex) jelly fish
P. 565
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Some Cnidarians go through stages in both body plans
o Both body plans have similar features
o one opening digestive system
o mouth / anus
o gastrovascular cavity
o food enters by the mouth
o digestion occurs in the gv cavity
o undigested waste exits via the mouth
the body wall has 3 layers
I)
Epidermis – outer layer
II)
Mesoglea – middle layer
III)
Gastroderm – inner digestive layer
-
around the mouth are tentacles
on the tentacles are stinging cells called nematocysts
each nematocyst is a poison filled sac containing a tightly coiled, spring loaded
dart.
Nematocysts are used to capture and immobilize prey
Used also for defense
Feeding / Digestion
carnivores
-
capture small prey with tentacles and nematocysts
some cnidarians have a relationship with photosynthetic protests to add to
nutrition intake
digestion is extracellular goes into the gastrovascular cavity, in a one opening system (Mouth/ Anus)
Respiration - diffusion
Internal Transport - diffusion
Excretion - diffusion
Responses
Nerve network- net
The nerve net is concentrated around the mouth
For feeding
Have chemoreceptors- detect chemicals
Mostly medusas have receptors for balance
Statocysts - balance
Medusas have receptors for detecting light – ocelli
Movement
do not have muscle cells
epidermal cells change shape to allow movement
Reproduction
Asexual
o Mostly budding
o Mostly polyps
o However, a budding polyp can produce either polyps or medusa
Sexual
o Sperm and/or eggs are released into the water
o Fertilization occurs in the water or in an egg carrying medusa
o Zygote grows into a ciliated larva, which swim to a suitable living
environment
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3 Classes of Cnidarians
1.
Class Scyphozoa
o live most of its life as medusa
ex) jellyfish
o still have both body plans
o most nematocysts are harmless to humans
*exception – Australian box jelly – can cause death in 3-20
minutes
2.
Class Hydrozoa
o most of its life as a polyp
ex) hydra, Portuguese man- of- war
o most live in branching sessile colonies
o in a colony specialized polyps will perform specialized functions
o some hydrazoans are hermaphrodites – has both sex organs
3.
Class Anthozoa
o only polyps
ex) sea anemones
o can have symbiotic relationships
ex) coral
o build an exoskeleton to protect them
either calcium carbonate or limestone
ex) sea pens
• colonies of polyps
Importance of Cnidarians
Symbiotic relationships
Coral reefs – ecological homes
Protect shorelines
Studied for medical research