13. radiate animals
TRANSCRIPT
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Radiate Animals
Chapter 13
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Radiate Animals
Phylum Cnidaria & Phylum Ctenophora
Radial Symmetry
Diploblastic 2 embryonic tissue layers
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Phylum Cnidaria
All animals except
sponges belong to
the clade
Eumetazoa, theanimals with true
tissues.
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Phylum Cnidaria
Phylum Cnidaria is
one of the oldest
groups in this clade.
Fossil history back700 MY.
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Phylum Cnidaria
Cnidarians have:
Radial symmetry
Gastrovascular cavity extracellular
digestion
Tissues derived from two embryonic
germ layers
Cnidocytes special cells with stingingorganelles called nematocysts.
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Phylum Cnidaria
Cnidarians have
diversified into a wide
range of both sessile
and floating formsincluding jellies,
corals, and hydras.
Polymorphism
some species existas both polyps and
medusae during their
life cycles.
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Phylum Cnidaria
The basic body plan of a cnidarian is a
sac with a central digestive
compartment, the gastrovascular
cavity.
A single opening functions as both mouth
and anus.
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Phylum Cnidaria
In colonial forms that
share a
gastrovascular
cavity, polyps maybe specialized for
feeding,
reproduction, or
defense.
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Body Wall
Cnidarians have an
outer tissue layer,
the epidermis,
derived fromectoderm, and an
innergastrodermis,
derived from
endoderm, withjellylike mesoglea in
between.
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Body Wall
The epidermal layer contains several types of
cells organized into tissues.
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Reproduction
Polyps can reproduce asexually by
budding, fission, or pedal laceration.
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Reproduction
Cnidarians, typically medusae, can also reproduce
sexually.
A zygote usually develops into a motile planula larva.
Some species only exist as polyps, others only asmedusae, others alternate between the two.
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Feeding
Cnidarians are carnivores that use tentacles tocapture prey.
The tentacles are armed with cnidocytes uniquecells that function in defense and the capture of prey.
Nematocysts contain toxins used for prey capture anddefense.
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Feeding
Nematocysts are
used to inject a
toxin.
Variable in form.
May be used for
prey capture or
defense.
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Feeding
Extracellular digestion begins in the
gastrovascular cavity, but is completed
within the cells of the gastrodermis.
Some cnidarians supplement their diet
with nutrients collected from algal
symbionts (zooxanthellae).
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Nerve Net
Cnidarians have a diffuse nervous
system.
Nerve cells forming two interconnected
nerve nets in the epidermis andgastrodermis.
No concentrated grouping of nerve cells
forming a central nervous system. No advantage for radially symmetrical animals
where stimuli approach from all sides.
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Classification
The phylum Cnidaria is divided into four
major classes:Class Hydrozoa Class Scyphozoa Class Cubozoa ClassAnthozoa
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Classification
A fifth class, Staurozoa, has been
proposed.
No medusae in life cycle but polyp topped
by medusa-like region.
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Phylum Cnidaria
Class Staurozoa Commonly called stauromedusans
No medusa stage.
Solitary polyp body that is
stalked. Uses adhesive disk to attach to
seaweeds, and objects on seabottom.
Polyp top resembles a medusa
with eight extensions (arms)ending in tentacle clusterssurrounding mouth.
Reproduce sexually.
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Class Hydrozoa
Hydrozoans are
variable in form.
Mostly marine.
Usually colonial,sometimes solitary.
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Class Hydrozoa Typical Life Cycle
Most hydrozoans alternate between polyp
and medusa forms.
Some have only polyps.
Some have only medusae.
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Class Hydrozoa - Polyps
Typical hydroids have abase, a stalk, and one ormore terminal zooids(individual polyp animals).
Thecate presence of aprotective cup aroundthe polyp. Obelia
Athecate no suchprotection. Ectopleura
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Class Hydrozoa - Medusae
Hydroid medusae are usually
smaller than those in the
class Scyphozoa.
Gastrovascular cavity is
continuous from mouth totentacles and is lined by
gastrodermis.
Velum, inward projection of
the bell, is present. Specialized organs:
Statocysts equilibrium
Ocelli light sensitive
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Class Hydrozoa
Members of the order
Siphonophora, such as
the Portuguese man-of-
war, are actually colonies
of polyp individuals.
One polyp may be gas
filled and used as a
float.
Feeding polyps each
with one long tentacle
Reproductive polyps
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Class Hydrozoa
Hydrocorals
resemble true corals.
Calcareous
skeleton Fire coral
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Class Scyphozoa
In the class
Scyphozoa, jellies
(medusae) are the
prevalent form of thelife cycle.
No velum present.
Rhopalium sense
organ containingstatocysts and
sometimes ocelli.
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Class Scyphozoa
Tentacles around
the periphery of the
bell contain
nematocysts used toparalyze prey
animals.
In the center are four
frilly oral arms usedto capture and ingest
prey.
C S f
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Class Scyphozoa Typical Life
Cycle
Planula larvae
develop into a
polyp-like form.
Saucer-likebuds called
ephyrae are
produced by
strobilation.
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Class Cubozoa
In the classCubozoa, whichincludes box jelliesand sea wasps, the
medusa is box-shaped and hascomplex eyes.
Polyps are tiny anddevelop directly intomedusae.
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Class Cubozoa
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Class Anthozoa
Class Anthozoaincludes thecorals and seaanemones which
occur only aspolyps nomedusa stage.
All marine
Solitary orcolonial
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Sea Anemones Order Actinaria
Found in coastal
waters all around the
world.
Attach to rocks usingtheirpedal disc.
Feed on fish or any
other food of suitable
size.
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Sea Anemones Order Actinaria
Sea anemones usually move by gliding slowly
along on their pedal discs.
When a predator approaches, most withdraw.
Stomphiadetaches its disc and swims away.
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Sea Anemones Order Actinaria
Tentacles arranged around the central mouth.
The gastrovascular cavity is divided into sixradial chambers.
Increases the surface area of the gastrodermis.
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Mutualisms
Sea anemones sometimes harbor
zooxanthellae (photosynthetic protists)
like hard corals do.
Some crabs will decorate their shells
with anemones.
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Mutualisms
Some damselfish (anemone fishes) form
associations with large anemones.
Fish gains protection from living in the
anemone. The fish may help ventilate the anemone, or
keep it free of sediment.
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Hexacorallian Corals
Hexacorallian
corals (Order
Scleractinia)
are the true orstony corals.
Like tiny
anemones living
in calcareouscups.
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Hexacorallian Corals
Hexacorallians(SubclassHexacorallia) havea gastrovascular
cavity subdivided bysepta in multiples ofsix.
The calcium
carbonate skeletonis secreted belowliving tissue.
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Hexacorallian Corals
Polyps may be retracted into the skeleton.
Often retracted during the day.
The polyps expand for feeding.
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Tube Anemones and Thorny Corals
Members of
subclass
Ceriantipatharia.
Have coupled butunpaired septa.
Tube anemones
Solitary and live in
soft sediments.
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Tube Anemones and Thorny Corals
Thorny or black corals
Colonial and attach to firm substrata.
Both groups have few species and live in
warmer seas.
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Octocorallian Corals
Members of theSubclass Octocorallia
have eight pinnate
tentacles and eight
septa.
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Octocorallian Corals
Sea fans, sea pens & sea pansies belong to
this group.
Often beautifully colored.
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Cnidaria
MedusozoaAnthozoa Staurozoa Scyphozoa Cubozoa Hydrozoa
Trachyline-
like
hydrozoaGut with
septalfilament
sSiphonoglyph
Anthozo
an
pharynx
Hexaradial
and
octaradialsymmetry
Creeping
planula
without cilia
Strobilation Complex eyes
Velarium
Boxlike
medusa body Polyp lost
Velum in medusae
Medusae produced by
lateral
budding and entocodonMedusoid body form
Motor nerve net
Primary polyp tentacles hollow
Mouth surrounded by solid tentaclesPlanula larva
CnidocytesRadial, polypoid body form
RhopaliumPolyp
reduced
or lost
Hydroids Man-of-war Other
hydrozoa
Phylum Cnidaria
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Coral Reefs
Coral reefs are one of the most productive
and diverse ecosystems on Earth.
Found in shallow tropical seas.
They require warm water. Sunlight required for symbiotic zooxanthellae.
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Coral Reefs
The main structure of
the reef is calcium
carbonate secreted by
hermatypic (reef-
building) corals and
coralline algae.
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Coral Reefs
Octocorallian corals and some
hydrozoans (those known as fire coral)
also contribute calcium carbonate.
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Types of Reefs
Fringing reefs are close to a landmass with
no lagoon or a narrow lagoon.
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Types of Reefs
Barrier reefs run parallel to shore and have a
wide, deep lagoon.
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Types of Reefs
Atolls are reefs that encircle a lagoon, but
not an island.
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Types of Reefs
Patch reefs are scattered throughout a
lagoon.
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Reef Zones
The fore reef slope, orreef front, is the side thatfaces the sea. Slopes into deeper water.
The reef crest is the shallow or even slightly emergenttop of the reef.
The reef flat is the shallow back reef area that slopesinto the lagoon.
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Coral Reefs
Nutrients from fertilizerand sewage threatencoral reefs withexcessive algal growth.
Coral reefs in manyareas are threatenedby factors mostly ofhuman origin.
Higher atmospheric concentrations of carbondioxide (from burning hydrocarbon fuels) tendsto acidify ocean water, which makesprecipitation of CaCO3 by corals more difficultmetabolically.
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Coral Reefs
Symbiosis betweenzooxanthellae and coralsis threatened by globalwarming. Warmer water damages the
photosynthetic mechanismin zooxanthellae.
Coral tissues turn white and
brittle, this is called coralbleaching.
Zooxanthellae die or areexpelled by corals.
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Phylum Ctenophora
Phylum
Ctenophora are
the comb jellies.
No nematocysts. Tissue level of
organization, like
cnidarians.
Mostly freeswimming.
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Phylum Ctenophora
They use theirciliated combplates forswimming.
Not strongswimmers.
Ctenophores arebioluminescent.
Statocystsense organ
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Phylogeny
Cnidarians may have evolved from a radiallysymmetrical planula-like ancestor.
Trichocysts and toxicysts found in some
ciliates may be precursors to nematocysts.