Transcript zly 103 on radiata

THE RADIATE ANIMALS
• PHYLUM CNIDARIA
• - Classes Hydrozoa, Scyphozoa, Anthozoa
& Cubozoa
• PHYLUM CTENOPHORA
• - Class Tentaculata
• - Class Nuda
CLASSES OF PHYLUM CNIDARIA
• CLASS HYDROZOA eg Hydra,
Obelia
• CLASS SCYPHOZOA eg Aurelia
aurita (Jelly fish)
• CLASS ANTHOZOA eg Sea
anemones, Corals
• CLASS CUBOZOA eg Tripedalia
cystophora, Sea wasp
GENERAL CHARACTERISTICS
OF PHYLUM CNIDARIA
• Have simplest degree of structural and
functional organization
• Exclusively marine, few sp in fresh water
• Are acoelomates (lack coelom)
• Radially symmetrical
• There is diversity of body types found among
the members of this phylum.
• Has 2 distinct layers ie Ectoderm and
Endoderm
BODY CAVITY DIVERSITY(FROM ACOELOMATES THROUGH
PSEUDOCOELOMATES TO COELOMATES)
WHY ARE CNIDARIAN ACOELOMATES?
• Coelom
(also
called
the
body
cavity)
cavity within the body of all animals higher than the coel
enterates and certain primitive worms.
• Formed
by
the
splitting
of
the
embryonic mesoderm into two layers.
• In mammals it forms the peritoneal, pleural, and pericard
ial cavities.
• Cnidarian lacks this quality & are therefore Acoelomates
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•
In Pseudocoelomates, body cavity is incompletely lined by mesoderm eg in Rotifera &
Nematoda.
Coelomates begin from Mollusca then Annelids, Arthropods, Echinoderms & Chordates
GENERAL CHARACTERISTICS
OF PHYLUM CNIDARIA
• Tentacles around the mouth
• Tissues level of organization
• No choanocytes (flagellated collar cells of the
sponges)
• Alternation of generation with 2
morphologically distinct stages:
• Polyp (sessile, remain attached, asexually
reproducing form)
• Medusa(motile, sexually reproducing form)
GENERAL CHARACTERISTICS
OF PHYLUM CNIDARIA
• No excretory or respiratory organs
• Nerve net with symmetrical & asymmetrical
synapses
• Gastrovascular cavity used for both digestion
and excretion.
• Mesoglea (jelly-like substance between the two tissue layers
(epidermis & gastrodermis) for support).
• Hydostatic Skeleton - chitinous, calcerous, or
protein.
GENERAL CHARACTERISTICS OF PHYLUM
CNIDARIA
• Radiata have only two embryonic tissue layers.
• Specifically, no mesoderm (the tissue that gives
rise to structures, including muscles, in
triploblastic organisms).
• Lack sophisticated movement seen in
triploblastic organisms.
• Mouth: both ingestion & egestion- no anus
• Asexual reproduction by budding in polyps
• Sexually by gametes in all medusa & some
polyps
DEFENSE IN CNIDARIANS
• Cnidarians also have cnidocytes (specialized
cells that function in defense & capture of prey)
• Cnidocytes contain organelles called cnidae,
which are able to evert (extend or retract).
• Cnidae that sting are called nematocysts.
• These nematocysts can immobilize fish for
capture, and they can also be used for defense.
FEEDING MECHANISMS IN
HYDROZOAN: HYDRA
THE HYDROZOA eg Hydra
vulgaris
• Class Hydrozoa includes hydras and the
infamous
Portuguese
Man-of-War,
an
organism noted for its potent sting, in the
medusa form.
• Most Hydrozoans exist in the polyp and
medusa forms.
• For example, some hydrozoan eg Obelia exist
as an asexually reproducing polyp that
alternates with a sexually reproducing medusa
form (see next slide).
Obelia life cycle
Dimorphism & Polymorphism in
Cnidarians
• A striking & puzzling feature
• Dimorphism: existence in polyp &
medusa
• Polymorphism: colonies of some species
have
morphologically
differing
individuals each specialized for certain
roles eg feeding, reproduction & defense.
Differences between Medusa & Polyp
Polyp
• Sedentary or sessile life
• Non free swimming
• Has tubular body
• Simple body structure
• Velum absent
• Mouth is circular
• Mesoglea poorly developed
Medusa
• Adapted for a floating life
• Free swimming
• Bell or umbrella-shaped
• Complex structure
• Velum present
• Mouth rectangular
• Mesoglea highly developed
Note: Medusae possessing a velum are called veiled or craspedote medusae.
Scyphomedusae have no velum & are acraspedote.
Polyp vs Medusa
Polyp vs Medusa
Class HYDROZOA eg Hydra
Body plan of Hydra
Body plan of Hydrozoa: Hydra
Body plan of Hydra
• Epidermis consist:
• Epitheliomuscular cells (can self-reproduce) for
covering & muscular contraction
• Interstitial cells: differentiate to form the cnidoblast,
sex cells, buds, nerve cells.
• Gland cells- located around the basal disc and mouth,
secrete adhesive substance for attachment
• Cnidocytes- contain nematocyst for catching prey
• Sensory cells found around the mouth for detection
of stiimuli
• Nerve cells- synapse with sensory cells & other nerve
cells
Body plan of Hydra
• Gastrodermis consist:
• Nutritive-muscular cells all tall. columnar, large and
vacuolated with flagella at one end & microvilli at the
other end
• Interstitial cells: can transform to form other kind of
cells when the need arises.
• Gland cells- surround the mouth to aid feeding &
digestion.
• Mesoglea lies btw the epidermis & dermis and act
like a type of elastic skeleton
Biology of Hydra: Hydrozoans
• May be solitary or colonial
• Found in freshwater
• Hydra, unlike other hydrozoa exist as
solitary(no medusa or colonial forms).
• Cylindrical body shape
• Body size depends on level of contraction
and extension.
MOVEMENT OF HYDRA
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Somersaulting- Can be found hanging downward
Walking
Looping
Floating
Climbing
Gliding
Swimming
Feeding &Nutrition In Hydra
• Use Tentacles to capture & direct the food
• Exclusively carnivorous feeds on cylops,
annelids, crustaceans, insect larvae.
• Digestion in enteron (gastrovascular cavity)&
is both
• Extracellularly- the prey is killed by the action
of digestive enzymes from gland cells of
gastodermis
• Intracellularly- occur in the gastrovascular
cavity
Feeding & Nutrition in Hydra
cont’d
• Tentacles have many cnidoblasts in them
for capturing prey
• Nematocysts: Immobilize & paralyze the
prey
• Inside the gastrovascular cavity, gland
cells secrete enzyme to digest the food.
• Egestion via the mouth.
Reproduction in Hydrozoa: Hydra
• Mostly dioecious(male & female separate)
• Reproduce both sexually & asexually by
budding. Has power of regeneration
• Zygote undergo holoblastic(complete) cleavage
to form the blastula.
• Cleavage is indeterminate(regulative)
• Fertilization: Cyst formed around the embryo
which break loose from parent to form the
young hydra.
BIOLOGY OF OBELIA
• Unlike Hydra, has both colonial &
medusa form
• It’s a plant-like Hydrozoa
• Whitish in colour under microscope
• Largely carnivorous
• Use tentacles to capture prey
• Digestion both extra & intracellular
BIOLOGY OF OBELIA
• Dioecious
• Fertilization is external
• Mouth open into manubrium
• Zygote forms planular larva
• Statocyst are gravity receptor for
maintenance of balance
The life cycle of Obelia, an Hydrozoan
Classification & Diversity of Hydrozoa
• Order Hydroida eg Hydra
• Polyploid stage predominant, medusa short-lived
or absent, sense organ exclusively ectodermal
• Order Trachylina eg Craspedacusta
• Polyploid stage redused or absent, medusa large,
dominant, sense organs endodermal
• Order Hydrocorallina eg Millepora
• fixed, colonial polyploid in which the coenosarc
secretes CaCO3, polyps is dimorphic with slender
dactylozoids and short plump gastrozoids
Body plan of Scyphozoa: Aurelia aurita
Life Cycle of Jelly fish- Aurelia
aurita
CLASS SCYPHOZOA
Jellyfish
eg
• a.k.a cup-animals with umbrella or bowlshaped
• May attain a bell diameter of more than 2m
• Most scyphozoans range from 2 to 40cm in
diameter
• May be colourless, orange or blue
• Exists predominantly in the medusa form
• Mesoglea unusually thick giving the bell a
fairly firmed consistency
BIOLOGY OF CLASS SCYPHOZOA
eg Jellyfishes
• Predominantly Medusa, polyp form occurs
only as small larva during life cycle stage.
• Thaumatosyphus hexaradiatus are unusual
member because medusa are sessile, attached
to seaweed
• Movement is by rhythmical pulsation of the
umbrella
• Tentacles may be few or short as in Aurelia
aurita or long as in Cyanea
BIOLOGY OF CLASS
SCYPHOZOA eg Jellyfishes
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Aurelia aurita is common member
No velum or nerve rings
Oral arms bears the nematocysts
Have sense organ called rhopalium
Each rhopalium has two olfactory pits
Nervous system has a nerve net with subumbrella
net that control bell pulsations
• The nerve net is concentrated to form ganglia at
the base of rhopalia
• Tentaculocyst is the organ of balance
BIOLOGY OF CLASS
SCYPHOZOA eg Jellyfishes
• Sexes separate
• Sperm carried by ciliary current into
gastric pouch of female
• Internal fertilization
• Reproduction& Life cycle: The medusa
sperm + egg = Zygote
• Ciliated Planular larva emerge =
Scyphystoma (hydra-like form)= Strobila
= Ephyra to adult.
Classification & Diversity of Scyphozoa
• Order Stauromedusae eg Lucernaria
• Bell, goblet or trumpet shaped, sessile attached by
an aboral stalk, no marginal sense organ or
tentaculocyst.
• Order Coronatae eg Periphyla
• Bell conical shaped, divided by a deep circular
coronary groove, tentacles long, borne on pedalia
• Order Discomedusae eg Aurelia, Pelagia
• Flat saucer or disc-like umbrella, 8 tentaculocysts
present, square-shaped mouth extending into 4
long oral arms.
Class: Anthozoa
Sea anemone
CLASS ANTHOZOA
• Eg sea anemones, corals , and sea fans.
• Anthozoans are all polyps, no medusa ie Not
Dimophic
• Symbioses between reef-building corals and the
dinoflagellates.
• In these relationships, corals provide housing and
protection for the protists, and the dinoflagellates
provide food for the corals.
• Members of all of the Cnidarian classes can respond
to external stimuli and can use stinging nematocysts
for prey capture and defense.
Anthozoa characteristics
• Flower-shaped, body structure more complex
than Hydrozoans
• Exclusively polyploid, no medusa
• Most advanced of all marine Cnidarian
• Mouth lead to pharynx
• Gastrovascular cavity subdivided by septa, or
mesenteries partioned into chamber
• Mesoglea stout with cells and fibres
• Skeleton secreted in the form of coral
• Nematoblast found in the body layers
Life Cycle of Anthozoa- Sea
anemone
Biology of Anthozoans
• Feeding
• Similar to Hydra polyp
• Aided with tentacles, cnidoblast and
nematocyst.
• Pharynx lined with lateral ciliated grooves
• Movement by rhythmic contraction of
muscles, mesoglea and water in gastric
cavity
Biology of Anthozoans eg Sea
anemones
• Move by gliding slowly along the substrate
on their pedal disc
• Are carnivorous
• Can expand & stretch their tentacles to
catch the prey
• Nematocysts immobilizes the prey
• Pharynx with ciliated grooves: siphonoglyps
• When disturbed, can contract & withdraw
their tentacles and oral discs.
Biology of Anthozoans eg Sea
anemones
• Reproduction
• Sexes are separate
• Gonads borne on the margin of
septa/mesenteries
• Reproduction by sexual & asexual means
• Asexual reproduction can occur by pedal
laceration or at times budding
• Fertilization occurs in enteron or externally:
Planular larva emerge
Biology of Anthozoans eg Sea
anemones
• Oral end is an expanded oral disc
• The mouth is often elongated with a ciliated
groove (siphonoglyph) at one or both ends.
• Gastrovascular cavity is sub-divided by 8 or
more septa or mesenteries
• Mesenteries with nematocysts and gastrodermal
gonads.
Classification & Diversity of Anthozoa
• Order Stolonifera eg Clavularia
• Polyp arising independently from a creeping mat
or stolon, skeleton of calcerous tubes or separate
calcerous spicules or absent.
• Order Telestacea eg Teleston
• Lateral polyps on simple or branch stems arising
from a creeping base, skeleton of calcerous
spicules or absent.
• Order Coenothecalia eg Heliopora
• Polyploid embedded & connected by solenial
tubes, skeleton massive, calcerous & blue green
from iron salts.
Diversity in forms
• HYDROZOA
• Life history features both Polyp and Medusa stages,
Mesoglea non cellular
• SCYPHOZOA
• True Jellyfishes have conspicuous medusoid form,
Polyploid larva stage, Mesoglea thickened with fibres
and cells
• ANTHOZOA
• Sea anemones, coral are all polyps, Mesoglea stout
with fibres and cells
CHARACTERISTIC FEATURES OF PHYLUM
CTENOPHORA
• Biradial symmetry
• Ellipsoidal or Spherical in shape with
radially arranged rows of comb plates for
swimming.
• Nematocysts absent & replaced by
Colloblasts
• No polymorphism or dimorphism
• Mouth, pharynx, stomach and anus present.
• Reproductive stage involve free swimming
cydippid larva
CLASS CUBOZOA
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Most recently classified
Exist as both Polyp & Medusa
Medusa is the predominant form of this class
Cubozoa medusa may be about 25cm tall
Medusa are stronger swimmer and voracious
predator
• Base of each tentacle form pedalium
• Tentacle(s) present in each corner of umbrella
margin
Class Cubozoa
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Medusa dominant
Polyp state develop directly to medusa
Bell margin with velarium
Tetramerous (four part radial symmetry)
Bell may be cube or square--shaped with tentacles
arising from each corner.
• Gonads are endothermal (found in the gatrodermis)
• Specialized sense organ called rhopalium
CLASS CUBOZOA
• Class Cubozoa are the box jellies, which have
a box-shaped medusa form.
• Some species in this group are among the most
venomous organisms in the world
• Their stings can be fatal to humans
Structure of Class Cubozoa
Life Cycle of Cubozoa
SIMILARITIES OF CNIDARIA
WITH CTENOPHORA
• Radial symmetry
• Well developed gelatinous
collenchyme
• No coelom cavity
• No organ systems
• Diffuse nerve plexus
Differences between Cnidarians
& Ctenophores
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No nematocysts
Comb plates and colloblasts present
Pharynx & Anal openings present
No polymorphism or dimorphism
Do not exist as colonies
Biology of representative type of
Ctenophora: Class tentaculata
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Eg Plerobranchia is a representative of this grp
Body size: 1.5 to 2.0 cm in diameter
The oral pole bears the mouth
The aboral pole bears the sensory organ
called the Statocyst
Movement in Ctenophorans : The Comb Plates
• Pleurobranchia has 8 equally spaced bands of
comb rows on the body surface.
• Each band consists of transverse plates of long
fused cilia called the Comb plates
• Cilia beating on the comb plates propels the
animal around (movement).
• The beat starts from aboral end to the oral
aiding swimming.
• All the 8 combs beat in unison.
• Backward movement possible
Comb plates of Ctenophora
Ctenophora body plan
Ctenophora comb plate
Tentacles of Ctenophora
• Has 2 long, solid & extensive tentacles
• May be about 15cm long when fully
extended
• The tentacle surface bear colloblasts
(glue cells).
• The colloblasts secrete substances to
catch and hold the prey
Body wall of Ctenophora
• Collenchyme lies between epidermis
and gastrodermis
• It fills most part of the interior wall
of Ctenophores
• Contain muscle fibres and amoeboid
cells
Digestion and Feeding in Ctenophora
• Feed on plankton such as copepods
• Gastrovascular cavity consists of mouth,
pharynx, stomach.
• Gastrovascular canal branches to the
comb plates.
• Two blind canals terminate near the
mouth.
• Aboral canal ends in 2 anal canals
Nervous system in Ctenophorans
• Similar to Cnidarians
• The sense organ is located at the aboral pole(
statocyst).
• No central coordination as found in higher
animals.
• A calcareous statolith
• The epidermis bears abundant sensory cells
• Sensitive to chemical & other stimuli
Reproduction & Development in
Ctenophorans
• All monoecious (male & female organs in
one animal)
• Gonads located on the lining of
gastrovascular canal under the comb plates.
• Cleavage is determinate
• Fertilization: free swimming Cydippid
larva
• Cydippid larva develops directly to an
adult