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Cnidaria
Jellyfishes, Anemones, and Corals
Phylum Cnidaria
• Gr. knide, nettle; + L. aria,
like or connected with
• 9000 + species
• 5 classes
–
–
–
–
–
Anthozoa
Staurozoa
Scyphozoa
Cubozoa
Hydrozoa
Characteristics of Cnidaria
• Cnidocytes present
• All aquatic, most marine
• Radial symmetry
• Polyps and Medusae
• Adults are diploblastic with
epidermis and gastrodermis
• Mesoglea (jelly) lies
between the two layers
• Incomplete gut gastrovascular cavity
• Extensible tentacles circle
the mouth
Characteristics (continued)
• Muscular contractions via
epitheliomuscular cells
• Sense organs: statocysts
and ocelli
• Nerve Net
• Asexual reproduction by
budding in polyps forms
colonies and clones
• Sexual reproduction in all
medusae and some polyps
• No excretory or respiratory
systems
• No coelom
• Cnidocytes
• Cnidae - specialized
organelles in cnidocytes
– ~ 20 different types of
cnidae
– Nematocysts are the most
common type of cnidae
Cnidarians and Symbiosis
• Zooxanthellae in
hermatypic corals
– Photosynthesis feeds the
host
– Recycle phosphorus and
nitrogenous waste
– Enhance deposition of
calcium carbonate
– Only found in shallow warm
waters between 30 N and
30 S latitude
• Crabs
• Anemone Fish
• Nomeus
Class Anthozoa
•
•
•
•
•
Gr. anthos, flower
All polyps, no medusae
All marine
Solitary or colonial
Gastrovascular cavity
divided by mesentaries or
septa
Fig. 13.22
Fig. 13.25
Fig. 13.23
Fig. 13.29
Fig. 13.27
CO 13
Fig. 13.28
Fig. 13.30
Fig. 13.31
Fig. 13.32
Fig. 13.33
Fig. 13.34
Fig. 13.35
Class Staurozoa
•
•
•
•
All polyps, no medusae
All marine
Solitary
Polyp has a stalk and
attaches via an adhesive
disc
• Polyp’s top resembles a
medusa
Class Scyphozoa
•
•
•
•
•
Polyp reduced or absent
All marine
Solitary
Medusae without velum
Margin of bell usually with
eight notches equipped
with sense organs
Fig. 13.19
Fig. 13.17
Class Cubozoa
•
•
•
•
Polyp reduced
All marine
Solitary
Medusae square in crosssection
• Tentacles attached to bladelike pedalium
• Velarium present, no velum
• Complex eyes
Class Hydrozoa
• Asexual polyps, sexual
medusae
• Marine and freshwater
• Solitary or colonial
• Hydranths without
mesenteries
• Medusae with velum
Fig. 13.11a
Fig. 13.11b
Fig. 13.8
Fig. 13.15
Fig. 13.16
Fig. 13.14
Fig. 13.10
Fig. 13.12
Fig. 13.7
Fig. 13.9
Ctenophora
Comb Jellies
Phylum Ctenophora
• Gr. ktenos, comb; + phora,
bearing
• 8 rows of combs
• Colloblasts - adhesive cells
for capturing prey
• Biradial symmetry
• Complete gut
• Two extensible tentacles in
most
• Muscle cells
Fig. 13.36
Fig. 13.39
Fig. 13.37a
Fig. 13.37c
Fig. 13.37b
Fig. 13.37d