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Phylum Cnidaria
General Characteristics
About 9000 species
_____________________
Simple nervous system
__________________
Diploblastic organization
Endoderm
Ectoderm
General Characteristics Cont’d• Either tubular or bell shaped
• _______________________
• Only animal with
cnidocytes
• Cnidocytes-specialized
stinging cells (on tentacle)
• _______________________
• All marine (aquatic)
____________________________
• Cnidarians’ bodies are
organized around the
gastrovascular cavity,
where digestion takes
place
• GV has a single opening
that serves as both
mouth and anus
2 Layers of Cells
–Diploblastic:
•__________________________
–Gastrodermis: lines GV cavity
–Epidermis: lines the outside of
the body (the skin)
• In between the two layers is the
_________- a jelly-like substance.
Cnidarian Body Wall
Stinging Cells
• Have Cnidocytes
–________________
–Contain nematocysts: barbed
thread-like structures inside the
cnidocyte that shoots out and can
puncture and poison or entangle
prey
Cnidocyte
Feeding
• _______________________________
• Inner gastrodermis secretes digestive
juices into gastrovascular cavity which
digests food and circulates nutrients
Feeding Cont.
Nervous and Movement
•_________________
& sensory receptors
•Muscles help in
directional movement
& capturing prey
Life Cycles
• Cnidarians have two body forms that
are representative of the sexual and
asexual life cycles that they undergo.
–_______
–Medusa
Polyp
–_______
–_______
–Usually attaches to a substrate
at the aboral end
–Oral end is surrounded by
feeding tentacles
Medusa
_________
________________
Sexual (dioecious)
Shaped like an upside-down bowl
Tentacles surround the mouth that
is housed underneath the bell
• When cnidarians display both
forms at some point in their lives,
they are said to display an
__________________________
_________________________
Both sexual and asexual
Sexual
Gametes released into water
Fertilization takes place to
create free-swimming planula
Asexual
By budding
Generalized Cnidarian Life Cycle
__________________________
• Scyphozoa: Jellyfish
• Anthozoa: Sea anemones & Corals
• Hydrozoa: Hydra
• Cubozoa: Box Jellies
Class Hydrozoa
• Ex. Hydras
• __________________
• Includes hydras, fire corals, and
Portuguese Man of War
• Display alternation of generations
–Polyp
–Medusa
Class Scyphozoa
• True Jellyfish
• ___________________________
–Small polyp stage during life
cycle
_____________________
• Similar to Scyphozoans, except that
their medusa is cuboidal
• Includes the box jellyfish
–1 of the 10 most venomous
animals on the planet
–Kills 12 people per year
Class Anthozoa
• Polyps that are flower-like
• ___________________
• Includes sea anemones, corals,
sea whips, and sea fans