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Cnidarians & Ctenophores
(Cnidos) stinging nettle
Ch.7 Marine Biology Book
Ch.33-2 Biology Book
Mr. Werner - MATES
Phylum Cnidaria
Intro Video
• Cnidarians
• Biology of Cnidarians
Phylum Cnidaria
• Includes marine organisms such as
jellyfish, Portuguese man-of-war,
coral, sea anemone, & sea fans
• Hydra is a freshwater cnidarian
Phylum Cnidaria
• All carnivorous
• Have 2 cell layers (epidermis -outer &
gastrodermis-inner) with a hollow body called
gastrovascular cavity
• Contain a jelly-like layer between epidermis &
gastrodermis called mesoglea
• Single opening (mouth/anus) to
gastrovascular cavity where food & water
enter & wastes leave; called two-way digestive
system
• Have tentacles around mouth to pull in water
& capture food
Cnidarians (Fig.7.8)
 Have a simple nerve net to help with
movement & senses
 Medusae Have Statoctsts – control balance
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 Sessile members include corals, sea
anemones, & sea fans
 Have radial symmetry as adults
Contain stinging cells called cnidocytes in their
tentacles that contain coiled stingers called
nematocysts that can shoot out & paralyze
prey
Stinging cell
Cnidarian Body Forms (Fig.7.6)
• Have 2 basic body forms ---polyp &
medusa
• Polyp forms are usually sessile with
upright tentacles arranged around
the mouth at the top and with a thin
layer of mesoglea
• Corals, hydra, & sea anemones exist
in the polyp form as adults
Cnidarians
• Medusa forms are usually free-
swimming, bell-shaped animals with
tentacles that hang down
• Jellyfish & Portuguese man-of-war
are medusa form as adults
• Polyps are the asexual stage
• Medusa are the sexual stage
Cnidaria (Fig.7.7)
• Hydra structure
JELLYFISH LIFE CYCLE
Moon Jelly Life Cycle Video
Coral Reefs
• Most corals, like other cnidarians, contain a symbiotic
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algae called zooxanthellae, within their gastrodermal
cells.
The coral provides the algae with a protected
environment and the compounds necessary for
photosynthesis.
Most importantly, they supply the coral with organic
products of photosynthesis. These compounds, including
glucose, glycerol, and amino acids, are utilized by the
coral as building blocks in the manufacture of proteins,
fats, and carbohydrates, as well as the synthesis of
calcium carbonate (CaCO3).
Major coral reef sites are seen as red dots on this world map. Most of
the reefs, with a few exceptions are found in tropical and semitropical
waters, between 30° north and 30° south latitudes. (NOAA)
Types of Coral Reefs
Ctenophores
Phylum Ctenophora
• the name is pronounced with a silent "c", as
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"teen-o-four" or "ten-o-four"
comb jellies
eight rows of cilia arranged to form a stack of
combs, also called comb plates, or ctenes ("comb
bearer“).
Video 1 Video 2 – Blood-Belly Comb Jelly
Video 3 – BBC Coral Reef Danger
Video 3 – Arabian Sea
Ctenophores
• live only in marine waters
• 100-150 species
• may be seasonally much more abundant
in the spring and early summer
• typically planktonic, transparent and
unpigmented, and most swim by
synchronous beating of the eight rows of
comb plates
Coastal Ctenophores -3 groups
• 1. Cydippida -round or oblong in shape Pleurobrachia
• 2. Lobata -have a pair of highly
expandable lobes that are used as sticky
prey capture surfaces
• 3. Most beroids are in this genus
Pleurobrachia
Bolinopsis infundibulum
• Lobed Comb Jelly
Groups continued
• Beroids are elongate animals that may be
cylindrical or very flat, are often more
translucent than transparent, and may be
colorless or light pink or yellowish.
• Beroes open up like a sack to engulf their
prey, which is most typically other species
of ctenophores
Beroe Comb Jelly
Oceanic ctenophores
• defined by a combination of water
temperature, light availability, depth and
other factors
• more fragile that coastal species & can
break into a million pieces if touched
The ctenophore Deiopea is found near the surface around the world.
Notice the thin filamentous branches of the tentacles which trail along
the body from the mouth (top). (Approx length 5 cm).
• This dramatic ctenophore lives near the bottom at
depths around 1000 meters. It has not yet been named
by scientists. Although it looks conspicuously colored
when illuminated, there is practically no red light in its
habitat, so red is as good as black. When disturbed, this
species releases bioluminescent material into the water,
causing a confusing swarm of sparkling lights. Notice
also the darkly pigmented gut which masks the
luminescence of its prey. (Length >15 cm)
Ctenophore light-scattering and
bioluminescence
• produced by beating of the eight rows of
locomotory cilia
• this is simple light diffraction or scattering
of light by the moving cilia, not
bioluminescence
• Most (but not all) ctenophores are also
bioluminescent, but that light (usually blue
or green) can only be seen in darkness.
changing rainbow of colors running
down the comb
Feeding
• The tentacles of most cydippid and lobate
ctenophores are covered by specialized
microscopic sticky structures known as
colloblasts
• After prey capture, the tentacle with its
adhering captured-prey is contracted and
brought across the ctenophore's mouth for
ingestion
Source for Comb Jellies
• http://faculty.washington.edu/cemills/Cten
ophores.html