Intro to eumetazoa2012

1. Introduction to EumetazoaIntroduction to Eumetazoa
The ‘true animals’
True epithelium, definite body axes, specialized tissues
Chapter 6
EUMETAZOA

2. True EpitheliaTrue Epithelia
Chapter 6
EPITHELIUM – cell layer that covers surfaces, lines
internal cavities and spaces
With basal lamina, apical-basal polarity, cell-cell
junctions, immobile
Allows for establishment of regulated compartments
(connective tissue, gut lumen, coelom)
Epithelial cells control passage of materials
Environment under the epithelium can be chemically
controlled

3. True EpitheliaTrue Epithelia
Chapter 6
APICAL-BASAL POLARITY
BASAL LAMINA
HEMIDESMOSOMES
Epithelial Junctions
•AHDERING
•SEALING
• GAP

4. Epidermis, Gastrodermis & GutEpidermis, Gastrodermis & Gut
Chapter 6
EPIDERMIS – the outer skin; covers the surface of the
eumetazoan body
Secretory
Absorptive
Impermeable
GASTRODERMIS – stomach skin; epithelial layer that
lines the gut and joins the epidermis at the mouth
GUT – internal, epithelia-lined cavity; it is a regulated
compartment
• GUT LUMEN (CAVITY) – also regulated
compartment
• Allows EXTRACELLULAR DIGESTION
• Secretes digestive enzymes and absorbs products

5. Connective TissueConnective Tissue
Chapter 6
CONNECTIVE-TISSUE COMPARTMENT – lies between
the epi- and gastrodermis
May just be the basal lamina of the two epithelia
May be very thick
CONNECTIVE TISSUE – consists of ECM and cells; no
collective term for cells of the ECM
Sponges – mesohyl
Metazoans – blastocoel
Cnidarians – mesoglea
Bilateria – simply called ‘connective tissue’

6. Eumetazoan SkeletonsEumetazoan Skeletons
Chapter 6
Skeletons can:
Maintain body shape
Support or protect the body
Transmit force of muscle
contraction
Be internal or external
Be mineral, organic or both
Be fluid or solid

7. Fluid SkeletonFluid Skeleton
Chapter 6
HYDROSTATIC SKELETON – water-filled skeleton,
a.k.a. a hydrstat; cavity filled with water-based fluid
**This is a eumetazoan innovation!!**
• Surrounded by muscles (circular and longitudinal)
• Muscles contract and pressurize the fluid
• Water is incompressible
•CIRCULAR CONTRACTION – lengthens hydrostat
and stretches longitudinal muscles
• LONGITUDINAL CONTRACTION – shortens
hydrostat and stretches circular muscles
Utility  inflate body, extend parts, locomotion, burrowing

8. Fluid SkeletonFluid Skeleton
Chapter 6
Orthogonal Crossed-helical
• Body wall
strengthened by
inelastic fibers (like
collagen)
• Resists aneurisms

9. Solid SkeletonSolid Skeleton
Chapter 6
PLIANT SKELETON – made of materials that
are rubbery and elastic
RIGID SKELETON – made of materials
that resist a change of shape (bone/shell)
• Deform when stretched, spring back to original
shape
• Proteins, polysaccharides, water
• Use as CT in comb jellies, mesoglea in jellyfish,
hinges of bivalves
Insect framework, terrestrial and flying invertebrates, and
fast moving crustaceans of the ocean

10. Movement and Body SizeMovement and Body Size
Chapter 6
Cilia/FlagellaCilia/Flagella MusclesMusclesVS
Only in water
Associated with surface
area (effective when S/V is
large)
Small, lilliputian
invertebrates
Prone to surface friction
and viscous drag from
environement
Momentum stops when
ciliary/flagellar beat stops
Water, air, land
Associated with volume
Locomotion, can move
body parts with respect to
other body parts (ALL
ANIMALS DO THIS)
Effective when S/V is
small

11. MusculatureMusculature
Chapter 6
EPITHELIOMUSCULAR CELLS :
Arose from epithelium.
Actin-myosin microfilaments
allowed some to become
contractile.
MYOEPITHELIAL CELLS :
Contractile fibers isolated in
independent cells but are still part
of the epithelium.
Outside the basal lamina
MYOCYTES:
True muscle, contractile cells
below basal lamina.
No longer epithelial.

12. MusculatureMusculature
Chapter 6
SMOOTH MUSCLE :
Contracts slowly.
Tension over large range of
stretch lengths.
Contractile tentacles.
CROSS-STRIATED MUSCLE :
Contracts rapidly.
Tension over limited range.
Snapping jaws or claws.
OBLIQUELY-STRIATED :
Intermediate of the other two.
Extensible animals that can
make quick movements.
ANTAGONISTIC

13. Neurons and Nervous SystemNeurons and Nervous System
Chapter 6
Eumetazoans use nerve cells to
detect, evaluate, and respond to
environmental stimuli.
NEURONS - respond to stimuli
by transmitting information as a
wave of depolarization to the
target cells
Sensory receptors and neurons
arose from epithelia (like
muscle cells).
They became specialized and
migrated to a connective-tissue
compartment

14. Neurons and Nervous SystemNeurons and Nervous System
Chapter 6
Transmission of a nerve impulse from neuron to neuron
or from neuron to effector (muscle) occurs via:
Electrical junctions – gap junctions that join
cells so that membrane depolarization (action
potential) spreads uninterrupted; no
organismal control
SYNAPSE – gap between two cells (synaptic
cleft) through which the action potential is
carried by chemical neurotransmitters

15. Sense Cells & OrgansSense Cells & Organs
Chapter 6
Eumetazoans need to obtain a dynamic picture of their
environment so they can respond appropriately.
Response to different stimuli like:
Direction and distance to the source of the
stimuli are so important to each eumtezoan
ElectromagneticElectromagnetic MechanicalMechanical
ChemicalChemical MagnMagn eticetic
Simple: sensory neuron-effector
Complex: multiple stimuli, whole-body
response, accessory structures, CNS

16. Gravity ReceptorsGravity Receptors
Chapter 6
STATOCYSTS – hollow capsules
lined with MECHANORECEPTORS
and with a dense, heavy STATOLITH
at the center.
Gravity pulls the statolith against
the bed of mechanoreceptors
which then causes alterations of
the depolarization pattern.

17. PhotoreceptorsPhotoreceptors
Chapter 6
CILIARY and RHABDOMERIC – can be dispersed as
individual cells or, can be grouped together as EYES.
OCELLUS:PIGMENT SPOT
PIGMENT CUP – EVERTED or INVERTED

18. DevelopmentDevelopment
Chapter 6
ZygoteCleavage Blastula *Gastrulation* Larva
Gastrulation types:
INVAGINATION
EPIBOLY
INGRESSION

19. DevelopmentDevelopment
Chapter 6
DIPLOBLASTIC –
adults have 2
epithelial layers
(epidermis &
gastrodermis)
TRIPLOBLASTIC – adults have 3
epithelial layers (addition of
mesothelium)
MESODERM – located between
ecto- and endoderm and can arise
from either

20. GrowthGrowth
Chapter 6
SolitarySolitary ModularModularVS
• Juvenile grows via
general increase in size
• ALLOMETRIC – different
body parts grow at different
rates
• Surface > Volume
• Gills, lungs, gastrodermis
• Associated with
locomotion and increasing
complexity on one body
axis
• Self repair, often killed
Add new, small,
identical units (module –
ZOOID)
Clonal budding
All zooids form a colony
Favorable SA:V
ISOMETRIC – similar
growth
Colony is considered
one individual
Self repair, higher
survival if preyed upon

21. GrowthGrowth
Chapter 6

22. GrowthGrowth
Chapter 6
POLYMORPHISM – modular growth that results in
specialization of zooids with different forms and
functions (very common in Cnidarians)
Exemplifies the
replication-
specialization-
integration pattern
of metazoans