Transcript Zoology Chapter 7 Phyla: Cnidaria & Ctenophora

Zoology
Chapter 7
Phyla: Cnidaria & Ctenophora
Main focus on Cnidaria
Minor focus on Ctenophora
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Chapter 7 Homework
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Read Chapter 7
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Page 122-143
Do Review Questions 1-9,13,15-20
pages 143-4
Review website for terms/definitions
Review website for practice test
questions
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What’s a Cnidarian?
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A metazoan
Lineage ~700MY old
Named after cindocytes –
stinging cells
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Body plan simple, sac-like
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Most common type nematocyst
Symmetry is radial or biradial
Aquatic - mostly marine,
some freshwater species
Show tissue level of
organization
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Cnidarian Characteristics
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Symmetry – radial
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Polymorphism present
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No “head”
Has oral & aboral ends
Polyp (sessile) & medusa (free-swimming) body
types
Gastrovascular cavity
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single opening (mouth/anus) surrounded by
tentacles
H2O w/i serves as hydrostatic skeleton
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Cnidarian Characteristics, con’t….
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Stinging cell organelles, cnidae, prevalent on
tentacles, epidermis, &/or gastrodermis
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Nerve net present, some sensory organs
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Nematocysts most abundant type
Statocysts – balance organs
Ocelli – simple light sensors
Muscle fibers present
Reproduction
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Asexual: budding (polyp)
Sexual: planula larvae (medusa, some polyp forms)
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Individuals may be monoecious or dioecious
No excretory or respiratory systems; diffusion
suffices
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Medusa & Polyp Body Plans
Mouth & anus are the same opening
Oral End 
Aboral End 
Oral End 
Pedal Disc
Aboral End 
Digestion extracellular in gastrovascular cavity; smaller particles ingested
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intracellularly
Ecological Relationships
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Food source for mollusks & fish
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Habitats:
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Some ctenophores, mollusks, & flatworms will
eat hydroids w/ nematocysts
Coral reefs home to fish, arthropods
Hydroids attach to underwater structures
Commensalism on mollusk shells
Aquatic organisms provide food source for
cnidarians
Rarely provide food for human consumption
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Polymorphism: the presence in a species
of more than one structural type of individual
Polyp: hydroid form; sessile;
Medusa: umbrella shaped; freeaboral end attached to substrate swimming
by pedal disc
Body tubular; mouth upward
ringed by tentacles
Body sac-like; mouth
downward; tentacles ring
umbrella
Asexual reproduction: budding,
fission, pedal laceration
Sexual reproduction occurs too
Reproduction sexual &/or
asexual
Medusa usually dioecious
Sea anemones & corals are
polyps – no medusa stage
Includes Scyphozoans &
Cubozoans
Locomotion: Hydras move
freely, polyps sessile, sea
anemones move on basal disc
Locomotion: medusa move
freely about, at mercy of waves
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Purpose of Cnidae
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Cnidarians mostly voracious carnivores, but
predatory capabilities hampered by body
plan. So….
Polyps rely on stinging cells to
capture/paralyze any organism the tide
brings by
Medusa rely on stinging cells to do same
even though they are free-swimming (realize
inability to totally control where they swim)
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Nematocysts
Stinging cells triggered by
mechanical or chemical stimuli
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Nematocysts in tentacles
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Nematocyst Discharge
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Cell generates osmotic pressure up to 140 atm that
causes the ejection to occur
Hydrostatic pressure increases as osmotic pressure
decreases
Due to high osmotic pressure, stimulus causes H2O
to rush in opening operculum
High hydrostatic pressure launches the thread
within 3 milliseconds with an acceleration power of
40,000 g and a penetration force of 20-33 kPa;
barbs point rear & anchor in victim’s tissue; poison
injected
Nematocysts are capable of penetrating up to a
depth of 0.9 mm
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Lost nematocyst must be replaced
Cnidarian toxin
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While the amount of toxin expressed by a single
nematocyst is minute, several thousand
nematocysts discharging at once have a significant
effect.
Functionally, the toxin causes Na+ and Ca++ ion
transport abnormalities, disrupts cellular
membranes, releases inflammatory mediators, and
acts as a direct toxin on the myocardium, nervous
tissue, hepatic tissue, and kidneys.
Specifically, the toxin may contain catecholamines,
vasoactive amines (eg, histamine, serotonin),
kinins, collagenases, hyaluronidases, proteases,
phospholipases, fibrinolysins, dermatoneurotoxins,
cardiotoxins, neurotoxins, nephrotoxins, myotoxins,
and antigenic proteins. The protein component of
the toxin tends to be heat labile, nondialyzable, and13
is degradable by proteolytic agents.
Demographics
of Cnidarian stings
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United States
Jellyfish stings occur most commonly during the summer
along coastal regions. As the coastal population grows and
more tourists come to the beaches, the frequency of jellyfish
sting is likely to increase. One investigator reported 500,000
annual envenomations in the Chesapeake Bay area and
200,000 annually along the Florida coast.
International
Jellyfish stings occur in tropical oceans, especially between
latitudes 30° south to 45° north, because of a high natural
concentration of cnidarians. This is especially true of the east
coast of Australia during the warm summer months between
November and May. (Don’t forget, they’re in the southern
hemisphere, so their summer is during our winter)
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Mortality/Morbidity
of Cnidarian stings
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Jellyfish stings usually are mild, except those
caused by species in the South Pacific, such as the
box jellyfish or Portuguese man-of-war. Exact
mortality and morbidity is not known because of
underreporting and the lack of an international
jellyfish sting registry.
However, a recent epidemiology study of 118
cases of jellyfish stings from the Texas gulf coast
showed 0.8% had no effect, 80.5% had minor
effects, and 18.6% had moderate effects.
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Box Jellyfish Stings
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Box jellyfish venom has a median lethal dose of 40 mcg/kg,
which makes it the most potent marine toxin. The venom may
kill a person weighing 70 kg within 3 minutes and is
responsible for a mortality rate of 20%.
Box jellyfish venom has caused 72 deaths secondary to
respiratory paralysis, neuromuscular paralysis drowning, and
cardiovascular collapse.
The pain and spasms spread centrally as the venom travels to
the central circulatory system, inducing parasympathetic
overstimulation and respiratory-cardiac arrest.
Most fatalities occur within 20 minutes of the envenomation;
according to animal studies, approximately 5-10 mcg/kg of
venom is required to induce cardiac arrest.
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Other Cnidarian Stings
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The sting of the Portuguese man-of-war is
more painful than a common jellyfish sting. It
has been described as feeling like being
struck by a lightning bolt, and some victims
dread it more than a shark bite. This sting
has been responsible for 2 reported deaths.
The Arctic jellyfish is the largest, with
tentacles reaching 200 ft, allowing the
jellyfish to sweep an area slightly larger than
a basketball court.
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Cnidarian Nerve Net
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Contains 2 nerve nets at base of epidermis
and gastrodermis which connect
Nerve impulses carried by neurotransmitters
via snapses
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Transmission can go either direction
Lack myelin sheath around axons
No brain, no centralized nervous system
Sense organs simple
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Statocysts & ocelli
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Statocysts
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The statocyst is a balance organ present in some
aquatic invertebrates (Cnidarians, Ctenophores,
Bilaterians). It consists of a sac-like structure
containing a mineralized mass (statolith) and
numerous innervated sensory hairs (setae).
The statolith possesses inertia, causing the mass
to move when accelerated. Deflection of setae by
the statolith in response to gravity activates
neurons, providing feedback to the animal on
change in orientation and allowing balance to be
maintained.
Because organism has no “brain,” they are limited
in their actions and responses to stimuli. The
statocyst is therefore useful for telling the animal
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whether it is upside down or not.
Ocelli
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The phylum Cnidaria includes the first multicellular
animals to form eyes; this group exhibits a diversity
of eye designs ranging from a simple photosensitive
sheet of cells to the complex image forming eyes of
cubozoan jellyfish.
Because of their basal position on the phylogenetic
tree, cnidarians provide an excellent system in
which to study the evolution of the first multicellular
animal eyes and the evolution of photosensory
mechanisms.
The camera-type eyes of cubozoans represent the
most highly evolved eyes in the Cnidaria.
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Further they contain the visual pigments involved in
phototransduction: rhodopsin and opsins.
These eyes resemble the proposed ancestral prototype
eye.
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Cnidarian Classes
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Class Hydrozoa:
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Class Scyphozoa
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Marine, most medusa forms
Class Cubozoa
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Marine & freshwater, colonial, polyp & medusa
forms
Marine, medusa form prominent, no known
polyp forms, toxin lethal to humans
Class Anthozoa
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Marine, polyps only, no medusa form
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Class Hydrozoa
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Hydra & Obelia are good examples of this
class
Hydra:
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Freshwater species, 16 in N. America
Solitary polyps (typical form)
Eat larvae, worms, crustaceans
Asexual rep – budding;
Sexual Rep – prod of sperm/ova
Overwinter as cysts
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Obelia, colonial hydrozoan
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Colony has base, stalk, & terminal polyps
(zooids)
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Eat crustaceans, worms, larvae
Buds remain attached, incr colony size
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Gastrozooids (feeding)
Gonophores (reproduction)
Dactylozooids (defense, tentacles)
Medusa produced by asex. Budding, released
Medusa – dioecious, reprod sexually
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Planula larva attach, forming new colony
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Obelia Life Cycle
Alternation of generations of polyp and medusa stages
See Fig 7.9 in text
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Class Scyphozoa
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Most “jellyfish” belong here
Medusa body form
Marine, free-swimming (mostly), open sea
Aurelia example of scyphozoan
Dioecious, fertilization internal, planula
zygote
Zygote develops, forms buds (asexually)
which produce new medusa
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Class Cubozoa
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Box “jellyfish”
Note prominent “eyes”
Medusa dom body form
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Polyp form unknown
Strong swimmers, good hunters
Toxic venom
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Cubozoan
Pedalium: flat
blade at base
of each
tentacle
(see arrow)
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Class Anthozoa
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Sea anemones & coral found in this
class; another is sea pens
Medusa body form not seen
All are marine, shallow water dwellers
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Sea Anemones
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Polyps large, heavy
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Attach to substrate via pedal discs, may burrow
in sand/mud/silt
Tentacles ring the oral opening; mouth/anus slit
shaped
Reproduction: Sexual or asexual
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Monoecious & dioecious individuals
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Gonads internal; fertilization external
Zygote becomes a ciliated larva
Budding, pedal laceration, & fission may
produce new individual asexually
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Sea Anemones
Bonaire Giant Anemone 
Note fluorescence
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Commensal
relationships between
fish & anemone
Clown fish 
Pink Anemone Fish
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 Saddleback Clownfish
Coral
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Two types of corals:
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Brain Coral 
Zoantharian corals – true or stony corals
Octocorallian corals – soft corals, colonial
Both form coral reefs
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structures produced by living organisms. In most reefs the
predominant organisms are colonial cnidarians that
secrete an exoskeleton of calcium carbonate. The
accumulation of this skeletal material, broken and piled up
by wave action and bioeroders, produces massive
calcareous formations that make ideal habitats for living
corals and a great variety of other animal and plant life.
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Coral Reefs
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Coral reefs are estimated to cover 284,300
km2, with the Indo-Pacific region (including
the Red Sea, Indian Ocean, Southeast Asia
and the Pacific) accounting for 91.9% of the
total. Southeast Asia accounts for 32.3% of
that figure, while the Pacific including
Australia accounts for 40.8%. Atlantic and
Caribbean coral reefs only account for 7.6%
of the world total.
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Famous Coral Reefs include:
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The Great Barrier Reef - largest coral reef system in the world,
Queensland, Australia;
The Belize Barrier Reef - second largest in the world,
stretching from southern Quintana Roo, Mexico and all along
the coast of Belize down to the Bay Islands of Honduras.
The New Caledonia Barrier Reef - second longest double
barrier reef in the world, with a length of about 1500km.
The Andros, Bahamas Barrier Reef - third largest in the world,
following along the east coast of Andros Island, Bahamas
between Andros and Nassau.
The Red Sea Coral Reef - located off the coast of Israel,
Egypt and Saudi Arabia.
Pulley Ridge - deepest photosynthetic coral reef, Florida
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Zooxanthellae
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The coral polyps do not photosynthesize, but have
a symbiotic relationship with single-celled algae
called zooxanthellae
these algal cells within the tissues of the coral
polyps carry out photosynthesis and produce
excess organic nutrients that are then used by the
coral polyps.
Because of this relationship, coral reefs grow much
faster in clear water, which admits more sunlight.
Indeed, the relationship is responsible for coral
reefs in the sense that without their symbionts, coral
growth would be too slow for the corals to form
impressive reef structures.
Corals can get up to 90% of their nutrients from
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their zooxanthellae symbionts.
Interesting
Corals
Star Coral
Elkhorn Coral
Fluorescent
Coral
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Biodiversity of Coral Reefs
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Coral reefs support an extraordinary biodiversity; although
they are located in nutrient-poor tropical waters.
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The process of nutrient cycling between corals, zooxanthellae,
and other reef organisms provides an explanation for why coral
reefs flourish in these waters: recycling ensures that fewer
nutrients are needed overall to support the community.
Cyanobacteria also provide soluble nitrates for the coral reef
through the process of nitrogen fixation. Corals absorb
nutrients, including inorganic nitrogen and phosphorus,
directly from the water, and they feed upon zooplankton that
are carried past the polyps by water motion.
Thus, primary productivity on a coral reef is very high, which
results in the highest biomass per square meter, at 5-10g C m2 day-1.
Producers in coral reef communities include the symbiotic
zooxanthellae, sponges, marine worms, seaweed, coralline
algae (especially small types called turf algae.
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Cnidarian Picture Gallery
Red Stalk Jellyfish
Portuguese Man-o-War
This scyphozoan is unusual; it
is attached not free floating
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Velella
Velella &
Man-o-war
are only
scyphozoans
w/ floats
Note: Large float in this species
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Sea Pens (Anthozoans)
Orange Sea Pen
Note: Brittle star atop this sea pen 
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Sea Fan
Arctic Jellyfish
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x
Jellyfish washed ashore
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Phylum Ctenophera
(aka Comb Jellies)
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Marine, prefer warmer H2O
About 100 species known
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Size range: few mm to 1.5m
Medusa contains 8 rows of fused cilia
plates for locomotion
Some bioluminescent
Have 2 tentacles; only 1 species
known to have nematocysts
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Locomotion
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Comb plates extend from aboral to oral
end
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Fused cilia along plate which beat from
aboral to oral ends
All plates beat in unison, moving food
toward mouth
Two tentacles; long & retractable
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Surface bearing colloblasts which are
sticky
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Nervous & Reproductive
Systems
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No central nervous system
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Statocysts present for balance
Sensory cells in epidermis
Individuals are monoecious
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Fertilization external
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Some brood eggs
Larva free swimming
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Ctenophoran
Body plan
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Benthic
Ctenophoran

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X
x
“Tortugas Red”
Comb Jelly
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