phylum cnidaria - mr. davidson - behs science a/documents/phylum cnidaria.pdf · general...
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Phylum CnidariaTHE JELLYFISH, ANEMONES AND CORALS
General characteristics of phylum Cnidaria:
General characteristics of phylum
Cnidaria:
� Radial Symmetry
� Specialized Tissues
Sensory system- nerve net � Sensory system- nerve net
� Specialized cells stinging cells -cnidocytes
�Carnivores
�All aquatic, mostly marine
�Asexual and sexual reproduction
Fun Facts
� About 9000 species of cnidarians
� Oldest jellyfish, 500 million years old- found in Utah
Cnidocytes
Cnidocytes
� Stinging cells found in the tentacles
� Each cell has a tightly coiled, poison filed, dart-like structure-poison filed, dart-like structure-nematocyst
� Nematocyst has a trigger hair-cnidocil
� Contact with the cnidocil causes the nematocyst to discharge
� Fills with water
� Often has barbs
Tissue Structure
� Cells arranged
into tissues- two
layers
Outer layer: � Outer layer:
epidermis
� Inner layer:
gastrodermis
� In between layer
is jelly-like:
mesoglea
Body Plan
� Radial symmetry with central mouth
� Tentacles surround mouth and extend
from bodyfrom body
Life Cycle
� Most cnidarians have 2 body forms in
their life history
Life Cycle
�Polyp- asexual
and sessileand sessile
�Medusa-
dioecious and
free swimming
� VIDEO
� Birth of the Sea Nettle
� http://www.youtube.com/watch?v=NOf2RRmSkgQ� http://www.youtube.com/watch?v=NOf2RRmSkgQ
&edufilter=Ps5lSoPViR6fXm1RM5Eu1Q
� Arkive – Polyp Birth, Baby Swim
� Overview
� http://www.youtube.com/watch?v=O9Bl6TQmBE0&edufilt
er=Ps5lSoPViR6fXm1RM5Eu1Q
� /
Animal Functions
� Feeding
� Circulation
� Respiration� Respiration
� Excretion
� Response
� Movement
� Reproduction
� Video – Shape of Life
Feeding
� After stinging, prey is pulled into the
gastrovascular cavity
� Digestive chamber, 1 opening
� Extracellular digestion begins and � Extracellular digestion begins and
nutrients are absorbed
Feeding
� Cnidarians eat small crustaceans and fish
� Waste passes back out the mouth
VIDEO – ARKIVE� VIDEO – ARKIVE
Respiration, Circulation and
Excretion
� What do you think?
Respiration, Circulation and
Excretion
� Gastrovascular cavity brings oxygen in and waste
passes out
� Circulation is by diffusion from one cell to the next � Circulation is by diffusion from one cell to the next
Response - Senses
� Nerve net: Nerve cells that connect
around the bodyaround the body
� Cnidarians can feel touch
� Some have cells that sense gravity or light
� Coordinates movement and response
Movement
� Hydrostatic skeleton – muscles push
against water filled cavities
� Polyps can somersault or inch along
� Medusa swim or float
� VIDEO
� Anemone
� http://www.youtube.com/watch?v=Dm98n3908QM
� Dance of the Jellyfish
� http://video.nationalgeographic.com/video/animals/invertebrates-animals/other-invertebrates/dance-jellyfish-eorg
Reproduction
�Asexual
�Medusa bud from a polyp
�Polyps can bud other polyps
�Sexual
�External fertilization
�Males and females
�Eggs and sperm are released
into the water
Cnidarian Diversity
�Classes
�Hydrozoa�Hydrozoa
�Scyphozoa
�Cubozoa
�Anthozoa