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II. Phylum Cnidaria
31. Cnidarians have a
diploblastic organization
(tissues are derived from 2
embryological tissue layers,
endoderm and ectoderm).
32. The ectoderm gives rise
to the outer layer of the body
wall (epidermis)
33. The endoderm gives rise
to the inner layer of the body
wall (gastrodermis)
34. The jelly-like mesoglea
layer is between the
epidermis and gastrodermis.
35. Members of this phylum
have cell in their epidermis
called cnidia. These are
used for attachment,
defense, and feeding. It is a
fluid filled capsule.
• 36. Inside the capsule is a
hollow tube that is coiled up.
The capsule has a lid on one
end. Next to the lid is a
special cilia that acts like a
trigger. When something
touches the cilia it causes
the lid to open and out
shoots the tube.
37. There are many kinds of
cnidae. One of these is the
nematocyst. They have
poisonous spines that sting
when they penetrate the
prey.
38. Sometimes the tubes wrap
around the prey or they may
be covered with a sticky
material to help hold the
prey.
39. Most cnidarians have 2
forms during their life.
The Polyp and the
medusa.
40. The polyp is asexual
and attached.
41. It has a cylindrical
body called a column.
The oral end has a mouth
surrounded by tentacles
used to catch food.
42. The medusa
It is dioecious, free
swimming, has lots of
mesoglea.
The mouth is located in
the center facing down.
43. Cnidarians have a
gastrovascular cavity
where digestion occurs,
gas exchange happens,
gametes are discharged,
and waste is removed.
44. Cnidarians eat small
crustaceans and small fish
that it captures with its
tentacles. The food is taken
through the mouth into the
gastrovascular cavity.
45. Here it is dissolved.
Undigested food is removed
through the mouth.
46. Cnidarians have a
hydrostatic skeleton which
uses water or body fluid for
shape and support.
47. Reproduction
Most are dioecious.
Sperm and egg are
released into the
gastrovascular cavity or
the sea.
48. Embryos develop into
larvae called planula.
The planula floats around
until it attaches to a
substrate where it remains.
49. Class Hydrozoa
Nematocyst in epidermis
only.
Gametes are released out
to water.
50. Obelia forms colonies
with lots of branches. They
have two types of polyps. A
feeding polyp called a
gastrozooid. It has tentacles
used to catch food.
51. A gonozooid is a
reproductive polyp that
produces small medusa by
budding. These medusa
grow, reproduce sexually
and make new colonies of
polyps.
52. Physalia physalis, also
called the Portuguese manof-war, is a colony of
hydrozoa. It has a large float
that catches the wind and
moves it.
53. Class Scyphozoa
These are the true jelly-fish.
Their dominant life stage is
the medusa. Ex, Aurelia
54. Class Cubozoa
Active swimmers and
feeders.
Found in warm tropical
waters.
Deadly stingers. Ex.Chironex, the sea wasp.
55. Class Anthozoa
These are anemones and
corals.
Radial symmetry.
Anemone have an oral disk
surrounding the mouth at
the oral end.
56. Tentacles located here are
used to catch small animals
and pass them into the
mouth. The mouth leads to
the pharynx which leads to
the gastrovascular cavity.
57. The pedal disk is located
on the aboral end. It is used
to help attach the anemone
and the anemone can glide
around on it.
• Ex. Anthopleura
58. Pieces of the disk can
sometimes break of and
grow into a new anemone.
This is called pedal
laceration.
59. Anemones can be
monoecious or dioecious.
60. Corals come in many
shapes, colors, and sizes.
Some have mutualistic
relationships with an algae
called zooanthellae.
61. The algae provides
organic carbon and the coral
provides nitrogen and
phosphorus waste. The
coral uses the calcium to
build its skeleton.
62. Phylum Ctenophora
(comb jellies)
63. They have eight bands of
cilia from the oral end to the
aboral end. These are called
comb rows. They are used
for locomotion.
64. They capture prey using
tentacles. They have
contractile fibers used to
retract the tentacles
bringing the prey close to
sticky colloblasts that
capture and hold it.