2. • Phylum Cnidaria takes its name from the
Greek word “cnidos” which means nettle, a
stinging animal.
• The cnidarians all share the ability to sting
predators and prey.
5. BODY
• Cnidarians are radially symmetrical.
• One end of the body has an opening, the
mouth, which is surrounded by a ring of
tentacles.
• In a sessile cnidarian, called a polyp, a
stalk holds the tentacles upward.
• In a medusa, the tentacles dangle
downward from a free-swimming bell.
STRUCTURE
6.
7.
8. • In both body forms, the mouth leads to the
dead-end gastrovascular cavity.
• They have two germ layers: epidermis and
gastrodermis.
9. DIVER
• Corals and sea anemones belong to a
clade of cnidarians that exist exclusively
as sessile polyps.
• A second clade contains hydras and the
jellyfishes.
SITY
10. FEE
• Cnidarians are carnivores.
• Tentacles surrounding the mouth house
cells called cnidocytes, which act as tiny
harpoons that either inject venom or
entangle the prey.
• The tentacles sense, grab, and sting
passing prey, then stuff the meal into the
gastrovascular cavity.
DING
11. • Cells lining the digestive tract secrete
enzymes that digest the food.
• After absorbing the nutrients, the animal
ejects indigestible matter through the
mouth.
12. SUPPORT AND
• In all cnidarians, the two-layered body wall
acts as a hydrostatic skeleton.
• Although a cnidarian’s tissues do not form
organs such as a brain or muscles, these
animals can nevertheless make
coordinated movements as they swim or
capture prey.
MOVEMENT
13. • In the epidermis, groups of linked neurons
called nerve nets coordinate the
contraction of specialized cells.
• In this way, a jellyfish can force water out
of its bell to propel itself through water.
• The same mechanism enables a sea
anemone to stuff food into its
gastrovascular cavity.
16. EFFECTS ON
• Huge swarms of jellyfish are becoming
increasingly common, presenting a
nuisance for tourist destinations and
fisheries.
• Jellyfish stings may cause skin irritation or
cramps; a few species have toxins that
can be lethal on contact.
HUMANS
17. • On the positive side, coral animals secrete
calcium carbonate exoskeletons that have
accumulated over many generations to
build magnificent coral reefs.
• These unique ecosystems house many
commercially important species of fishes
and other animals, and they protect
coastlines from erosion.
• As they build their calcium carbonate
reefs, corals play an important role in the
carbon cycle.
18. • A molecule originally isolated from corals
(but now produced in the laboratory) is
being developed into a sunscreen for
human use.
19. CLASSES OF
1. Class Anthozoa
2. Class Scyphozoa
3. Class Cubozoa
4. Class Hydrozoa
CNIDARIANS
20. CLASS
• It includes all cnidarians that exhibit a
polyp body plan only.
• These animals are usually cylindrical in
shape and are attached to a substrate.
• A mouth opening is surrounded by
tentacles bearing cnidocytes.
ANTHOZOA
21. CLASS
• They live most of their life cycle as free-
swimming, solitary carnivores.
• They are dioecious animals, that is, the
sexes are separate.
• The life cycle of these animals can be
described as polymorphic, because they
exhibit both a medusal and polypoid body
plan at some point in their life cycle.
SCYPHOZOA
22. CLASS
• This class includes jellies that have a box-
shaped medusa, or a bell that is square in
cross-section.
• This is the most venomous group of all
cnidarians.
• They display overall morphological and
anatomical characteristics that are similar
to those of the scyphozoans.
CUBOZOA
23. CLASS
• Animals in this class are polymorphs, and
most exhibit polypoid and medusoid forms
in their life cycle, although this is variable.
• Many hydrozoans form colonies that are
composed of a branched colony of
specialized polyps that share a
gastrovascular cavity.
HYDROZOA
