35-2 Cnidaria and Ctenophora
 2 phyla of radially symmetrical
invertebrates.
 More complex than sponges
*have tissues and some simple
organs.
 All are aquatic.
 Most live in the oceans.
Phylum Cnidaria (cnidarians)
Freshwater
Jellyfish
Coral
hydra
Freshwater Hydra

Molecular
Expressions: Science,
Optics & You Olympus MIC-D:
Pond Life Digital
Movie Gallery - Hydra
(Coelenterata)
Jellyfish
Coral
Body Structures
 2 forms ( stages of life)
*V shape polyp: sessile,
like sponge
*Bell shape medusa:
swimming form
 p. 696 35-3
Medusa and Polyp
Body Structures
 2 cell layers (also known as germ layers)
*epidermis: outer layer of cells
*gastrodermis: inner layer of cells
esoglea: jellylike substance between
layers
Gastrovascular cavity: hollow gut
outh: single opening
 Tentacles: flexible extensions around mouth
Feeding and Defense
ll have cnidocytes
*Specialized cells for defense and capturing prey.
*Each cnidocyte has a nematocyst, which has a
long filament coiled inside it.
*When cnidocyte is “triggered”, the nematocyst
pushes filament out: capture prey with poison then
tentacles push prey into gastrovascular cavity
through the mouth. Enzymes digest the food,
lining of gut absorbs nutrients. The waste
products out through mouth.
Cnidocyte

To the right is a
nematocyst prior to
firing and
after. You can see
the stinging portion
which would
embedded in the
skin.
Nervous System
*Nerve net is a diffuse web of
nerve cells.
*No brain.
*Enables cnidarians to respond to
stimuli in the environment.
*Coordinates feeding and traveling.
Classification
3 classes under the phylum Cnidaria.
1. Hydrozoa: medusa form or polyp
form or both.
2. Scyphozoa: most of life as medusa
form.
3. Anthozoa: only as polyp form.
1. Class Hydrozoa
 3,700 species (fresh water and salt water
which means marine habitats)
Live as colonial organisms
Exs:
A.Obelia: all polyp forms
B. Portuguese Man-of-War: live as a
colony of polyps and medusa forms
C. Fresh water hydra
Obelia
Portuguese Man-of-War
Hydra
Only as polyp forms
Not colonial
1 to 4 cm in length
ost are white or brown, some green
because of symbiotic algae that live in it.
Attach to rocks or water plants in ponds
 Can move from one place to another
Asexual Reproduction
Done
by buds during
warm weather
Sexual Reproduction
 Only in the fall when temperatures are cool
 Eggs produced in ovaries
 Sperm produced in testes
 Either male or female or hermaphrodite
 Fertilized egg develops into embryo which
then forms into new hydra
2. Class Scyphozoa
 Cup animals
 Dominant life form is medusa
 200 species
Jellyfish (Aurelia)
 2 cm to 4 m
Life Cycle of Jellyfish
3. Class Anthozoa
 Flower animals
 6,100 marine species
Sea anemones and corals
Only in polyp form
Sea Anemones
ttach to rocks in coastal
areas
Feed on fish and smaller
animals that come near
their tentacles
ne exception: the
clownfish has a symbiotic
relationship with the
anemone. The tentacles of
the anemone protect the
clownfish from predators
and the clownfish drives
away other fish that would
eat the anemone.
Corals
Live in colonies
 Cements its calcium carbonate skeleton to each
other. When it dies, other polyps continue to live
on this foundation. Thousands of years later, a
coral reef is formed, but only the top layer is
living. This coral reef provides food and shelter
for fish and other invertebrates. Coral reefs are
usually in shallow depths, and in warm, clear
waters. The coral reefs have symbiotic algae that
live in them. This is one reason why they are in
shallow depths, so that the algae can
photosynthesize.
Corals
Corals
Phylum Ctenophora
 100 marine species
Comb holders
*comb-like rows of cilia
*look like jellyfish, so
sometimes called comb jellies
Difference from Cnidarians
 Do not pulsate through water but use cilia to
move
 Do not have cnidocytes but have colloblasts,
which secrete sticky substance, which sticks to
prey.
 Have sensory structure called apical organ at one
end of body.
 Most are hermaphrodites
 They are bioluminescent which means they are
able to produce light.
Comb Jellies
Review p.704 1-19, 21-25
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