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Intro to eumetazoa2012
1. Introduction to Eumetazoa
The ‘true animals’
True epithelium, definite body axes, specialized tissues
EUMETAZOA
Chapter 6
2. True Epithelia
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
Chapter 6
4. Epidermis, Gastrodermis & Gut
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
Chapter 6
5. Connective Tissue
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’
Chapter 6
6. Eumetazoan Skeletons
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
Chapter 6
7. Fluid Skeleton
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
Chapter 6
8. Fluid Skeleton
• Body wall
strengthened by
inelastic fibers (like
collagen)
• Resists aneurisms
Orthogonal Crossed-helical
Chapter 6
9. Solid Skeleton
PLIANT SKELETON – made of materials that
are rubbery and elastic
• Deform when stretched, spring back to original
shape
• Proteins, polysaccharides, water
• Use as CT in comb jellies, mesoglea in jellyfish,
hinges of bivalves
RIGID SKELETON – made of materials
that resist a change of shape (bone/shell)
Insect framework, terrestrial and flying invertebrates, and
fast moving crustaceans of the ocean
Chapter 6
10. Movement and Body Size
Cilia/Flagella VS Muscles
Only in water Water, air, land
Associated with surface Associated with volume
area (effective when S/V is Locomotion, can move
large) body parts with respect to
Small, lilliputian other body parts (ALL
invertebrates ANIMALS DO THIS)
Prone to surface friction Effective when S/V is
and viscous drag from small
environement
Momentum stops when
ciliary/flagellar beat stops
Chapter 6
11. Musculature
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.
Chapter 6
12. Musculature
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
Chapter 6
13. Neurons and Nervous System
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
Chapter 6
14. Neurons and Nervous System
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
Chapter 6
15. Sense Cells & Organs
Eumetazoans need to obtain a dynamic picture of their
environment so they can respond appropriately.
Response to different stimuli like:
Electromagnetic Mechanical
Chemical Magn etic
Direction and distance to the source of the
stimuli are so important to each eumtezoan
Simple: sensory neuron-effector
Complex: multiple stimuli, whole-body
response, accessory structures, CNS
Chapter 6
16. Gravity Receptors
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.
Chapter 6
17. Photoreceptors
CILIARY and RHABDOMERIC – can be dispersed as
individual cells or, can be grouped together as EYES.
OCELLUS:PIGMENT SPOT
PIGMENT CUP – EVERTED or INVERTED
Chapter 6
19. Development
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
Chapter 6
20. Growth
Solitary VS Modular
• Juvenile grows via Add new, small,
general increase in size identical units (module –
• ALLOMETRIC – different ZOOID)
body parts grow at different Clonal budding
rates All zooids form a colony
• Surface > Volume Favorable SA:V
• Gills, lungs, gastrodermis ISOMETRIC – similar
• Associated with growth
locomotion and increasing Colony is considered
complexity on one body one individual
axis Self repair, higher
• Self repair, often killed survival if preyed upon
Chapter 6
22. Growth
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
Chapter 6
