Chapter 13 Chapter 14
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Transcript Chapter 13 Chapter 14
Radiate Animals
Chapter 13
Radiate Animals
Phylum Cnidaria & Phylum Ctenophora
Radial Symmetry
Diploblastic – 2 embryonic tissue layers
Phylum Cnidaria
All animals except
sponges belong to
the clade
Eumetazoa, the
animals with true
tissues.
Phylum Cnidaria
Phylum Cnidaria is
one of the oldest
groups in this clade.
Fossil history back
700 MY.
Phylum Cnidaria
Cnidarians have:
Radial symmetry
Gastrovascular cavity – extracellular digestion
Tissues – derived from two embryonic germ layers
Cnidocytes – special cells with stinging organelles
called nematocysts.
Phylum Cnidaria
Cnidarians have
diversified into a wide
range of both sessile
and floating forms
including jellies,
corals, and hydras.
Polymorphism –
some species exist
as both polyps and
medusae during their
life cycles.
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.
Phylum Cnidaria
In colonial forms that
share a
gastrovascular
cavity, polyps may
be specialized for
feeding,
reproduction, or
defense.
Body Wall
Cnidarians have an
outer tissue layer,
the epidermis,
derived from
ectoderm, and an
inner gastrodermis,
derived from
endoderm, with
jellylike mesoglea in
between.
Body Wall
The epidermal layer contains several types of
cells organized into tissues.
Reproduction
Polyps can reproduce asexually by budding,
fission, or pedal laceration.
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 as
medusae, others alternate between the two.
Feeding
Cnidarians are carnivores that use tentacles to
capture prey.
The tentacles are armed with cnidocytes – unique
cells that function in defense and the capture of prey.
Nematocysts contain toxins used for prey capture and
defense.
Feeding
Nematocysts are
used to inject a
toxin.
Variable in form.
May be used for prey
capture or defense.
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).
Nerve Net
Cnidarians have a diffuse nervous system.
Nerve cells forming two interconnected nerve nets in
the epidermis and gastrodermis.
No concentrated grouping of nerve cells forming a
central nervous system.
CNS does not provide advantage for radially
symmetrical animals where stimuli approach from
all sides.
Classification
The phylum Cnidaria is divided into four major
classes:
Class Hydrozoa Class Scyphozoa Class Cubozoa Class Anthozoa
Classification
A fifth class, Staurozoa, has been proposed.
No medusae in life cycle but polyp topped by
medusa-like region.
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 sea
bottom.
Polyp top resembles a medusa
with eight extensions (“arms”)
ending in tentacle clusters
surrounding mouth.
Reproduce sexually.
Class Hydrozoa
Hydrozoans are
variable in form.
Mostly marine.
Usually colonial,
sometimes solitary.
http://youtu.be/MpSPdeTN74I
Class Hydrozoa – Typical Life Cycle
Most hydrozoans alternate between polyp and
medusa forms.
Some have only polyps.
Some have only medusae.
Class Hydrozoa - Polyps
Typical hydroids have a
base, a stalk, and one or
more terminal zooids
(individual polyp
animals).
Thecate – presence of a
protective cup around
the polyp.
Obelia
Athecate – no such
protection.
Ectopleura
Class Hydrozoa - Medusae
Hydroid medusae are usually
smaller than those in the class
Scyphozoa.
Gastrovascular cavity is
continuous from mouth to
tentacles and is lined by
gastrodermis.
Velum, inward projection of the
bell, is present.
Specialized organs:
Statocysts – equilibrium
Ocelli – light sensitive
Class Hydrozoa
Members of the order
Siphonophora, such as
the Portuguese man-ofwar, 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
Class Hydrozoa
Hydrocorals
resemble true
corals.
Calcareous
skeleton
Fire coral
Class Scyphozoa
In the class
Scyphozoa, jellies
(medusae) are the
prevalent form of the
life cycle.
No velum present.
Rhopalium – sense
organ containing
statocysts and
sometimes ocelli.
Class Scyphozoa
Tentacles around
the periphery of the
bell contain
nematocysts used to
paralyze prey
animals.
In the center are four
frilly oral arms used
to capture and
ingest prey.
http://youtu.be/aJUuotjE3u8
Class Scyphozoa – Typical Life
Cycle
Planula larvae
develop into a
polyp-like form.
Saucer-like buds
called ephyrae
are produced by
strobilation.
Class Cubozoa
In the class
Cubozoa, which
includes box jellies
and sea wasps, the
medusa is boxshaped and has
complex eyes.
Polyps are tiny and
develop directly into
medusae.
http://youtu.be/CCuNMIT67y8
Class Cubozoa
Class Anthozoa
Class Anthozoa
includes the corals
and sea anemones
which occur only as
polyps – no medusa
stage.
All marine
Solitary or colonial
Sea Anemones – Order
Actinaria
Found in coastal
waters all around
the world.
Attach to rocks using
their pedal disc.
Feed on fish or any
other food of
suitable size.
Sea Anemones – Order
Actinaria
Sea anemones usually move by gliding slowly
along on their pedal discs.
When a predator approaches, most withdraw.
Stomphia detaches its disc and “swims” away.
http://youtu.be/Dm98n3908QM
Sea Anemones – Order
Actinaria
Tentacles arranged around the central mouth.
The gastrovascular cavity is divided into six
radial chambers.
Increases the surface area of the gastrodermis.
Mutualisms
Sea anemones sometimes harbor zooxanthellae
(photosynthetic protists) like hard corals do.
Some crabs will decorate their shells with anemones.
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.
Hexacorallian Corals
Hexacorallian
corals (Order
Scleractinia)
are the true or
stony corals.
Like tiny
anemones
living in
calcareous
cups.
Hexacorallian Corals
Hexacorallians
(Subclass
Hexacorallia) have
a gastrovascular
cavity subdivided by
septa in multiples of
six.
The calcium
carbonate skeleton
is secreted below
living tissue.
Hexacorallian Corals
Polyps may be retracted into the skeleton.
Often retracted during the day.
The polyps expand for feeding.
Tube Anemones and Thorny Corals
Members of
subclass
Ceriantipatharia.
Have coupled but
unpaired septa.
Tube anemones
Solitary and live in
soft sediments.
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.
Octocorallian Corals
Members of the Subclass
Octocorallia have eight
pinnate tentacles and eight
septa.
Octocorallian Corals
Sea fans, sea pens & sea pansies belong to
this group.
Often beautifully colored.
Phylum Cnidaria
Cnidaria
Medusozoa
Anthozoa
Staurozoa
Gut with
septal
filaments
Scyphozoa
Strobilation
Complex eyes
Trachylinelike
hydrozoa
Hydroids
Man-of-war
Other
hydrozoa
Velarium
Boxlike
medusa body
Siphonoglyph
Anthozoan
pharynx
Hexaradial
and
octaradial
symmetry
Hydrozoa
Cubozoa
Creeping
planula
without cilia
Rhopalium
Polyp
reduced
or lost
Polyp lost
Velum in medusae
Medusae produced by
lateral
Medusoid body formbudding and entocodon
Motor nerve net
Primary polyp tentacles hollow
Mouth surrounded by solid tentacles
Planula larva
Cnidocytes
Radial, polypoid body form
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.
Coral Reefs
The main structure of
the reef is calcium
carbonate secreted by
hermatypic (reefbuilding) corals and
coralline algae.
Coral Reefs
Octocorallian corals and some hydrozoans
(those known as fire coral) also contribute
calcium carbonate.
Types of Reefs
Fringing reefs are close to a landmass with no
lagoon or a narrow lagoon.
Types of Reefs
Barrier reefs run parallel to shore and have a
wide, deep lagoon.
Types of Reefs
Atolls are reefs that encircle a lagoon, but not
an island.
Types of Reefs
Patch reefs are scattered throughout a lagoon.
Reef Zones
The fore reef slope, or reef front, is the side that
faces the sea.
Slopes into deeper water.
The reef crest is the shallow or even slightly emergent
top of the reef.
The reef flat is the shallow back reef area that slopes
into the lagoon.
Coral Reefs
Nutrients from fertilizer and
sewage threaten coral
reefs with excessive algal
growth.
Coral reefs in many areas
are threatened by factors
mostly of human origin.
Higher atmospheric concentrations of carbon dioxide
(from burning hydrocarbon fuels) tends to acidify
ocean water, which makes precipitation of CaCO3 by
corals more difficult metabolically.
http://www.youtube.com/watch?v=QAaRJKKTOys
Coral Reefs
Symbiosis between
zooxanthellae and corals
is threatened by global
warming.
Warmer water damages the
photosynthetic mechanism
in zooxanthellae.
Coral tissues turn white and
brittle, this is called coral
bleaching.
Zooxanthellae die or are
expelled by corals.
Phylum Ctenophora
Phylum
Ctenophora are the
comb jellies.
No nematocysts.
Tissue level of
organization, like
cnidarians.
Mostly free
swimming.
Phylum Ctenophora
They use their
ciliated comb
plates for
swimming.
Not strong
swimmers.
Ctenophores are
bioluminescent.
Statocyst – sense
organ
Phylogeny
Cnidarians may have evolved from a radially
symmetrical planula-like ancestor.
Trichocysts and toxicysts found in some ciliates
may be precursors to nematocysts.