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Phylum Cnidaria &
Ctenophora
Kingdom: Animalia
Phylum Cnidaria
Class Hydrozoa
Class Scyphozoa
Class Anthozoa
Phylum Ctenophora
Major Characteristics
 Presence of specialized tissues
 Also called Coelenterates
 Comprised of sea anemones, jellyfish, corals
 Have radial symmetry
 Two forms polyps and medusa
Body Structure
 All have radial symmetry, where similar
parts of the body are arranged and
repeated around a central axis
Radial vs. Bilateral Symmetry
Diagram A
Radial Symmetry
Two Main Body Forms - Polyp
 A polyp is a sac like
stage.
 Sessile or non-motile
Two Main Body Forms Medusa
 A medusa is bell-like,
which is similar to an
upside down
swimming polyp
 Free floating or
swimming
Polyp vs. Medusa
 Some spend their life
as both at some
point or as one or the
other the entire time
Diagram B
Polyp vs. Medusa
Diagram D
Three Basic Layers:
Three Basic Layers
 Ectoderm/Epidermis – outer layer that
contains the stinging cells
 Endoderm/Gastrodermis – lines the gut
 Mesoglea – Jelly like substance in
between the Ectoderm and Endoderm
which contains scattered cells and
collagen fibers
Exoskeleton
 Coral will create a
calcium carbonate
shell in which it will
live
Body Structure
 The mouth is located on the top of the polyp or underside
of the medusa
 It is the only opening on the organism so is also shares
the function of being an anus
Diagram E
Body Structure
Diagram F
Tentacles
 Slender finger like
structure used to
capture and handle
food
 Location of
nematocysts
Nematocysts
 The main
characteristic of
Cnidaria is the
presence of
nematocysts
 Stinging structures
found on the
tentacles
Nematocysts
 Coiled – like stinger
 Spring into the prey and
releases toxin
 Most not harmful to humans
because they cannot
penetrate skin
 Some fatal
Nervous System
 Main characteristic is the presence of a
nerve net
 Nerves cross over each other, at every
connection, communication occurs
 In humans millions cross over millions
and no communication occurs
Nerve Net
Diagram C
Digestive System
 All cnidarians are carnivorous
 Paralyzed by the nematocysts
 Enzymes in gastric cavity break down
the food and nutrients are absorbed by
cells in the endoderm
 Wastes are sent out the mouth/anus
Digestive System
Reproductive
 Cnidarians have the
ability to reproduce
sexually and
asexually
 One method that is
commonly seen is
budding
Class Anthozoa
 Largest group of
Cnidarians
 Stay in the polyp
stage throughout life
cycle
 Solitary or colonial
 Includes sea
anemones
Class Hydrozoa
 Can consist of just a
FLOAT
polyp stage, just a
medusa stage, or
both
 Can join together to
form complex
colonies such as the
Portuguese Man-OWar, which develop
floats
Class Scyphozoans
 Medusa is the dominant life stage
 Swim with rhythmic contractions of the bell,
though limited
 Contain the most dangerous/fatal stings
BELL
Phylum Ctenophora
 Comb Jellies
 Not a member of the
Cnidarian Phylum
even though they
share similarities
Cnidaria vs. Ctenophora
Ctenophora
 Have cilia at the
base of the medusa
to move
 Engulf food
 Do not have
nematocysts
 Have an additional
layer between endo
and ecto layers
 Anal pore