Polyp and medusa
Oral
Simple animals
Tentacle
Gastrovascular cavity
Mouth
Tom Hartman
www.tuatara9.co.uk
www.tuatara9.co.uk
Epidermis
Gastrodermis
Mesoglea
Mouth
Tentacle
Animal form and function 1
Aboral
Module
Module 11112
11112
Polyp
• Generally elongate with mouth and
tentacles uppermost and aboral end
attached to substrate.
• Generally sessile.
• Polyps often connect forming colonies.
Sometimes different polyps in a colony
specialize.
• Can use water as a hydrostatic skeleton.
Medusa
• Generally flattened swimming disc
or bell- shaped with mouth/anus in
centre of lower surface.
• Swim by pulsations with muscle
cells pulling against an elastic
mesoglea.
The life cycle of the hydrozoan
Obelia
Polyp and medusa
Reproductive
polyp
Feeding
polyp
• In many species the two body forms
alternate with the polyp multiplying
asexually and the medusa asexually.
Medusa
bud
Portion of
a colony
of polyps
Gonad
Medusa
ASEXUAL
REPRODUCTION
(BUDDING)
Key
1 mm
Haploid (n)
Diploid (2n)
1
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The life cycle of the hydrozoan
Obelia
The life cycle of the hydrozoan
Obelia
Reproductive
polyp
Reproductive
polyp
Feeding
polyp
Feeding
polyp
Medusa
bud
SEXUAL
REPRODUCTION
Portion of
a colony
of polyps
Medusa
bud
MEIOSIS
Gonad
Medusa
Egg
MEIOSIS
Gonad
Medusa
SEXUAL
REPRODUCTION
Sperm
ASEXUAL
REPRODUCTION
(BUDDING)
Portion of
a colony
of polyps
FERTILIZATION
Egg
Sperm
ASEXUAL
REPRODUCTION
(BUDDING)
FERTILIZATION
Zygote
Zygote
Developing
polyp
Mature
polyp
Planula
(larva)
Key
Haploid (n)
Diploid (2n)
1 mm
The immortal Turritopsis
• While colonial animals can have their
immortality, solitary individuals are
doomed to die.
• Hydrozoan cnidarians usually have a
complex life cycle, wherein a colonial
stage leads to the sexually mature,
solitary, adult stage.
The immortal Turritopsis
Key
Haploid (n)
Diploid (2n)
1 mm
Life cycle of a typical hydrozoan
• Eggs and sperm from
solitary, sexual, adult
medusa (jellyfish)
develop into an embryo
and planula larva, and
they then form the
colonial polyp stage.
• Medusae are formed
asexually from polyps.
These medusae have a
limited lifespan and die
shortly after releasing
their gametes
Shape and cells
• The hydrozoan Turritopsis nutricula has evolved a
remarkable variation on this theme, and in so doing
appears to have achieved immortality. The solitary
medusa of this species can revert to its polyp stage
after becoming sexually mature. In the laboratory,
100% of these medusae regularly undergo this
change. Thus, it is possible that organismic death
does not occur in this species.
• Turritopsis can do this because it can alter the
differentiated state of a cell, transforming it into
another cell type. Such a phenomenon is called
transdifferentiation, and it is usually seen only when
parts of an organ regenerate.
2
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The beginning of a third
layer.
Epidermis
• Muscular cells
• Interstitial cells
(stem)
• Cnidocytes
• Mucus gland cells
• Nerve net cells
• Sex cells
Gasterodermis
• Flagellate cells
• Enzyme gland
cells
• Mucus gland cells
• Nerve net cells
• (Symbiotic algae)
• In anthozoa the mesoglea has
amoebocytes.
The unique cell
Nematocysts
The namatocyst
Coral
•
•
•
•
•
•
•
No medusa (anthozoa).
Secrete Ca(CO3)2 into which
they are embedded.
Shallow water corals are
symbiotic with zooxanthellae
(often dinoflagellates).
Corals therefore have to
compete for light.
Great barrier reef is visible
from space.
Coral reefs hugely increase
‘ecospace’.
Hugely alter local geology.
3
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Phylum Ctenophora
• Radial symmetry
• Two cell layers with
gelatinous mesoglea in
which muscle fibres run.
• Eight rows of fused cilia.
• Muscular tentacles with
sticky spirocyst-like
organelles.
• Tissues but no organs.
• Complete gut!
• No polyp stage.
Flatworms and rotifers
Tom Hartman
www.tuatara9.co.uk
www.tuatara9.co.uk
Animal form and function 1
Module
Module 11112
11112
New levels of complexity 1.
Cleavage
• Leading hypotheses agree on major
features of the animal phylogenetic
tree.
• Zoologists currently recognize
about 35 animal phyla.
• New levels of complexity.
• Cleavage is spiral and determinate =
protostome development
• Cleavage is radial and indeterminate
= deuterostome development
Protostome development
(examples: molluscs, annelids,
arthropods)
Eight-cell stage
Spiral and determinate
New levels of complexity 2.
Fate of the Blastopore
• In protostome (spiral cleavage) development
– The blastopore becomes the mouth
• In deuterostome (radial cleavage)
development
Mouth
Anus becomes the anus
– The blastopore
Digestive tube
Mouth
Mouth develops
from blastopore
Anus
Anus develops
from blastopore
Deuterostome development
(examples: echinoderms,
chordates)
Animal pole
Eight-cell stage
Radial and indeterminate
Vegetal pole
New levels of complexity 2.
A new cell layer
• Triploblastic animals
• Blastocoel is ‘invaded
by cells as the gastula
matures.
• These mesenchyme
cells organise the
internal architecture
and some become the
mesoderm.
• Mesoderm spawns
organs and tissues
between the ‘skin’
and the ‘gut’.
4
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Gastrulation in a sea urchin embryo
Key
Gastrulation in a sea urchin
embryo
Key
Future ectoderm
Future mesoderm
Future endoderm
Future ectoderm
Future mesoderm
Future endoderm
Animal
pole
Blastocoel
Animal
pole
Blastocoel
Mesenchyme
cells
Mesenchyme
cells
Vegetal
plate
Vegetal
plate
Vegetal
pole
Vegetal
pole
Blastocoel
Filopodia
pulling
archenteron
tip
Archenteron
Blastopore
Mesenchyme
cells
50 µm
Gastrulation in a sea urchin embryo
Ecdysozoa
Key
Insects, cruscatea, myriapods, arachnids
Future ectoderm
Future mesoderm
Future endoderm
Animal
pole
Protostomes
Blastocoel
Mesenchyme
cells
Velvet worms
Round worms
Lophotrochozoa
Strange bivalves
Vegetal
plate
Snails, octopi, bivalves, etc.
Triploblastic
Bilateralia
Vegetal
pole
Blastocoel
Filopodia
pulling
archenteron
tip
Eumetazoa
Deuterostomes
Segmented worms
Flat worms
Wheel mouths
Lanclets, vertebrates, etc.
Archenteron
Blastopore
Starfish, urchins, etc.
Mesenchyme
cells
Radiata
Diploblastic
Archenteron
Ectoderm
Mesenchyme:
(mesoderm
forms future
skeleton)
Comb jellies
Blastocoel
50 µm
Blastopore
Mouth
Anemones, hydras, etc.
Digestive tube (endoderm)
Sponges
Parazoa
Anus (from blastopore)
Adult derivatives of the three
embryonic germ layers in vertebrates
Layers
• Animal embryos
– Form germ layers, embryonic tissues,
including ectoderm and endoderm.
• Diploblastic animals
ECTODERM
Ectoderm
– Have two germ layers.
• Triploblastic animals
– Have three germ layers:
mesoderm.
Endoderm
• Epidermis of skin and its
derivatives (including sweat
glands, hair follicles)
• Epithelial lining of mouth
and rectum
• Sense receptors in
epidermis
• Cornea and lens of eye
• Nervous system
• Adrenal medulla
• Tooth enamel
• Epithelium or pineal and
pituitary glands
MESODERM
• Notochord
• Skeletal system
• Muscular system
• Muscular layer of
stomach, intestine, etc.
• Excretory system
• Circulatory and lymphatic
systems
• Reproductive system
(except germ cells)
• Dermis of skin
• Lining of body cavity
• Adrenal cortex
ENDODERM
• Epithelial lining of
digestive tract
• Epithelial lining of
respiratory system
• Lining of urethra, urinary
bladder, and reproductive
system
• Liver
• Pancreas
• Thymus
• Thyroid and parathyroid
glands
5
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Where on the
tree?
Insects, cruscatea, myriapods, arachnids
Flat worms
Phylum Platyhelmithes
Ecdysozoa
Protostomes
Velvet worms
Round worms
Lophotrochozoa
Strange bivalves
Eumetazoa
Deuterostomes
Segmented worms
Flat worms
Wheel mouths
Lanclets, vertebrates, etc.
Starfish, urchins, etc.
Comb jellies
Radiata
Diploblastic
Parazoa
•
Snails, octopi, bivalves, etc.
Triploblastic
Bilateralia
Anemones, hydras, etc.
Sponges
1.
2.
3.
4.
5.
6.
7.
8.
Big changes from all animals branching
earlier.
Bilaterally symmetrical.
SuperTriploblastic in development.
phylum
Tissues and organs.
Bilateralia
Definite anterior end with cephalisation.
Simple nervous system and brain.
Many have eyes.
Muscular system/cilia for movement.
Free living and parasitic.
6
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