Transcript Lecture 6 - University of Toronto Mississauga

The body of a sea anemone is “a
hollow column ...closed at
the base ...at the top with an oral
disc that includes a ring of
tentacles surrounding the
mouth and pharynx”. “By closing
the mouth, the water in the internal
cavity –the coelenteron/GV –
cannot escape, and thus the
internal volume remains essentially
constant. The walls of an
anemone include a layer of circular
muscle fibres. Longitudinal muscle
fibres are found on the vertical
partitions called septa that project
radially inward into the
coelenteron, including robust
longitudinal retractor muscles
along with sheets of parietal
longitudinal muscle fibres adjacent
to the body wall.”
Fig.
5
Kier
Phylum Cnidaria
sea anemones,
corals, jellyfish etc.
“With the mouth closed,
contraction of the circular muscle
layer decreases the diameter and
thereby increases the height of
the anemone. Contraction of the
longitudinal (or R =retractor)
muscles shortens the
anemone and re-extends the
circular muscle fibres.”
“...with this simple muscular
arrangement a diverse array of
bending movements and height
change can be produced.”
• Connective tissue fibre reinforcement
• “The walls of many hydrostatic skeletons are reinforced
with layers of connective tissue fibres that control and
limit shape change. The fibres are typically arranged as
a ‘crossed-fibre helical connective tissue array’ in which
sheets of connective tissue fibres (often collagenous)
wrap the body or structure in right- and left-handed
helices. Even though the connective tissue fibres are
typically stiff in tension and are thus relatively
inextensible, such an arrangement actually allows
length change. Elongation and shortening is possible
because the pitch of the helix changes during
elongation...”
Phylum Echinodermata
radially rather than
bilaterally symmetrical,
with oral and aboral
surfaces.
Water vascular system is unique to
these animals among phyla; it is a
vessel system filled with coelomic
fluid. ‘Arm vessels’ arise from a
tubular ring canal. In an asteroid
(starfish) five radial canals branch,
one into each of the arms.
Ambulacral groove on underside of
each arm lined with tube feet also
called podia.
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Asteroid echinoderms have an exoskeleton. In their dermis are embedded calcareous plates called
ossicles (inorganic salt Calcium Carbonate is the material). The skin thus consists of stiff relatively
shape-stable elements, in a matrix of flexible collageous fibres (i.e., connective tissue): tough, solid,
thick yet flexible protective armour.
Above each tube foot, within the arm, is a vesicle called an ampulla, encircled by ampullar muscles;
contraction of ampullar muscles will displace fluid out of the ampulla into the tube foot because fluid
is incompressible. There is a valve in the side branch to the radial canal – a one-way valve -- that
closes to prevent backflow of the fluid into the water vascular system. So for each ampulla +tube foot
as it operates the volume of fluid in the ampulla and tube foot lumen is fixed because the one-way
valve closed. But this fixed volume of fluid moves back and forth from ampulla to tube-foot lumen;
the system in the starfish is HYDRAULIC rather than hydrostatic as in earthworm segments.
From Brown,
Selected
Invertebrate
Types
Circumferential stress in a
pressurized cylindrical vessel (e.g.,
worm, tube foot) is exactly double
the longitudinal stress ‘Kier’s Law’.
Stress distribution in a fluid-filled
cylinder is not uniform (as per
annelid metameres): hoop stress
[force acting to increase diameter] is
twice as large as longitudinal stress.
Imagine it as it isn’t: no helical
array in the tube foot wall.
When the ampulla pushes fluid
into the podium lumen there
will be an increase in diameter
rather than a lengthening
Rosette of ossicles with
intrinsic musculature that
pulls up the disc middle
creating suction to
substratum.
End of extensible cylinder is the disc, larger in diameter than the
stem. There is a central depression.
Santos, R. et al. 2005. Adhesion of
echinoderm tube feet to rough
surfaces. J. exp. Biol. 208: 25552567.
Fig. 6 External morphology of
unattached pedal discs of
Paracentrotus lividus (left) [sea
urchin] and Asterias rubens
[starfish] (right) .
Temporary adhesion: the epidermis of the disc contains glands which produce two secretions:
glue/bonder and de-bonder, i.e., adhesive secretions and de-adhesive secretions. The glue is
delivered through the disc cuticle to the substratum where it forms a thin film bonding the foot. The
debonding secretions act as enzymes, detaching the upper coat of the glue and leaving the rest of
the adhesive material behind attached to the substratum as a footprint.
Importance of tube
foot in predation
Virginia Living Museum
‘off the beaten path’
Pulling with tube feet
adhering and starfish arm
muscles to open the
protective valves of
shellfish Mollusca
An interesting picture of razor clams
packaged for sale in a chinatown
market in Philadelphia
Phylum Mollusca
Razor clam burrowing
Winter A.G. et al. 2012. Localized fluidization burrowing mechanics of Ensis
directus. Journal of experimental Biology 215: 2072-2080.
(See also Inside JEB, Kathryn Knight. 2012. Razor clams turn soil into quicksand
to burrow.)
Blood and foot sinuses serve as hydraulic burrowing mechanism.
• Cycle of burrowing movements Fig. from Winter: In stage A, adductor relaxed so
shells braced on surrounding sand by ligaments; protractors start to contract (B)
pushing blood into foot and the foot probes down, gaining ground into the mud;
pushing force of foot makes body move up a little (C) (relative to dashed line).
• Stage D, adductors contract, pulling valves together, (red indicates the space they
DID occupy), pushing blood into foot to make an anchor, simultaneously squirting
seawater out around valves from mantle; this water* ‘puddles’ sand; foot swells
with blood into this quicksand region– the localized fluidation; displaced blood is
swelling the foot maximally into the bottom anchor of the TWO ANCHOR SYSTEM.
Cycle renews (F).
*Its not clear whether
this involves ocean
water drawn in by
siphons; perhaps it does
if the clam is burrowing
near the surface and
perhaps if lower down it
oscillates (?) its valves
to draw in pore water
(Winter)
Muscular hydrostats
Kier p.1252 Tongues, tentacles, trunks: “lack
the fluid-filled cavities and fibre-reinforced
containers that characterize ... hydrostatic
skeletal support systems” rather they are:
“a densely packed, three-dimensional array of muscle and connective tissue fibres”
Transverse sections showing the muscular arrangement of three examples of
muscular hydrostats.
A. Squid tentacle: T, transverse muscle fibres; L , longitudinal; transverse in the
tentacle core, “and extend to interdigitate with bundles of longitudinal muscle
fibres, notice the suckers.
Kier W M J Exp Biol 2012;215:1247-1257
©2012 by The Company of Biologists Ltd
Transverse sections showing the muscular arrangement of three examples of muscular
hydrostats.
B. Elephant Trunk: R, radials ‘extend from centre of the trunk between bundles of
longitudinal muscle that are more superficial, notice nasal passages.
Kier W M J Exp Biol 2012;215:1247-1257
©2012 by The Company of Biologists Ltd
C. Monitor lizard tongue. Circular muscle fibres surround two large bundles
of longitudinal fibres.
• “The muscle fibers are typically arranged so that all three dimensions of
the structure can be actively controlled, but in several cases such as the
mantle of the squid [of which more later] and some frog tongues, one of
the dimensions is constrained by connective tissue fibers.”
• “Because muscle tissue, like most animal tissues lacking gas spaces, has a
high bulk modulus, selective muscle contraction that decreases one
dimension of the structure must result in an increase in another
dimension. This simple principle serves as the basis upon which diverse
deformations and movement of the structure can be achieved” (Kier
2012).
• Read carefully all the section on muscular hydrostats by Kier: complex
bending achieved by interplay of contracting muscles --more subtle than a
passive uniform fluid in a chamber – i.e., some muscles by contracting can
affect the bulk modulus presented to other muscles that are acting upon
its incompressibility.
*bulk modulus of a substance measures its resistance to uniform compression Wikki
Muscular hydrostats (Kier contin.)
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Selective contraction: “This simultaneous contractile activity is necessary to
prevent the compressional forces generated by the longitudinal muscle from
simply shortening the structure, rather than bending it, and can actually augment
the bending by elongating the structure along the outside radius of the bend.”
“The longitudinal muscle bundles are frequently located near the surface of the
structure, as this placement away from the neutral plane increases the bending
moment.”
Helically arranged muscle fibres can be present and generate torsion.
https://youtu.be/K2G7L5hcEt8
See this URL for an animation
of Echinodermata body plan,
especially water vascular
system
Hydrostatic skeletons of Nematoda
Pseudocoelom locomotion
CFHCTA and adaptive volume of a fluid-filled cavity
Nematodes
Speciose: 20,000 described
More than a million to go.
What is the most famous nematode
and what is it most famous for?
“…if all the matter in the universe except the
nematodes were swept away, our world would still be
dimly recognizable, and if, as disembodied spirits, we
could then investigate it, we should find its mountains,
hills, vales, rivers, lakes and oceans represented by a
film of nematodes. The location of towns would be
decipherable, since for every massing of human beings
there would be a corresponding massing of certain
nematodes. Trees would still stand in ghostly rows
representing our streets and highways. The location of
the various plants and animals would still be
decipherable, and had we sufficient knowledge, in
many cases even their species could be determined by
an examination of their erstwhile nematode
parasites."
from "Nematodes and Their Relationships", 1915
Nathan Augustus Cobb, father of American
nematology.
See next slide: C. elegans: for being the first Animalia whose genome was entirely sequenced.
Pseudocoelom as fluid skeleton Caenorhabditis elegans*
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Phylum Nematoda Roundworms
pinworms: most too small (<2mm) to
leave any impression: ‘never seen a
nematode’.
Most free-living in soil; some parasitic.
Nematodes in the ocean? They are
internal parasites of whales.
Unsegmented, i.e., not metameric
Circular/ellipitical body in transverse
section, pointed ends (burrowing?)
HAVE NO CIRCULAR MUSCLES,
ONLY LONGITUDINAL.
Very high internal pressure of
pseudocoel fluid.
Locomotes lying on
Its side and arching
Its body about.
Jon Eisenback
*
Uniformity of body design
• Though the number of nematode species is so great, they are
unusually (in comparison to other phyla) uniform in body design,
i.e., they seem to conform to some important physical constraint (?).
“Characteristic features …are largely independent of size, of diet
and of stage of development [of free-living or parasitic existence].”
“…the elementary student may be forgiven …for thinking …there is
only one nematode, but that the model comes in different sizes and
with a great variety of life histories. (Harris & Crofton 1957)”.
• Recall D’Arcy Thompson is associated with the idea that along with
evolution mechanical principles constrain form. “A bridge, a ship, an
aeroplane are recognizable at once because their design is based
necessarily and largely on the mechanical forces which play such a
predominant part in their economy” (Harris & Crofton 1957).
• It is suggested that the conservative nature of nematode shape is
dictated by mechanical considerations. Being an elongated
unsegmented, high internal pressure pointy ended cylinder with no
circular muscles is the result of physical constraints related to its
locomotion.
“a structure composed of inextensible fibres [can]
accommodate large extensibility” (Shadwick 2008)
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After Kier, start with this paper which explains the essence of nematode
movement and from a historical perspective.
Shadwick R.E. 2008. Foundations of animal hydraulics: geodesic fibres
control the shape of soft bodied animals. J. exp. Biol. 211: 289-291.
Shadwick is discussing the importance of classic work by Clark &
Cowey.
Clark R.B., Cowey J.B. 1958. Factors controlling the change of shape of
certain nemertean and turbellarian worms. J. exp. Biol. 731-748.
Harris J.E., Crofton H.D. 1957. Structure and Function in the
nematodes: internal pressure and cuticular structure in Ascaris. J. exp.
Biol. 34: 116-130.
Worm as a fibre-reinforced cylinder
Clark-Cowey model “one of the key design principles of structural systems in
biology” (Shadwick 2008)
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From the 1950s the concept has existed of a hydrostatic skeleton: “a
system in which muscles shorten to act against a contained volume of fluid,
rather than rigid skeletal elements [sclerites, bones] to maintain shape and
effect movement” (op. cit.) The important role of collagen helices (‘springs’)
is more recent and begins with Clark & Cowey.
“…a structure composed of inextensible fibres [can] accommodate large
extensibility” is the basic idea of the classic Clark & Cowey paper (Shadwick
2008).
“…how [did a pseudocoelomate]… move if it had only one set of muscles as
in the case of nematodes” (op. cit.)
“…the geometry of the reinforcing fibres in the body wall was the key to the
solution…”. An antagonist of the longitudinal muscles of nematodes is a
collagen fibre helix in the cuticle.
[ memonic device ‘CFHCTA’ Canadians For Happy Carefree TAs : crossed
fibre helical connective tissue arrays (Kier).]
Screen demo
The Clark-Cowey model as explained by Kier, but see also Shadwick
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A: imagine the worm
aslength
a segment of a model worm, represented as a cylinder (radius r, length l) wrapped
(A) A unit
one unit
full turn of an inextensible fibre having length D; fibres with the opposite sense are
fluid-filled cylinderbyone
omitted.
long, its wall stiffened by
one turn of a collagen fibre
B represents
helix.
the unit
There is a (helical) fibre
length of the
angle ø: as the segment
worm cut
lengthens, cylinder diameter
along the top
and ø both decrease [at 0°
cylinder is a thread]; as the
and laid open,
segment shortens, its
D being the
diameter and ø both
fibre length.
increase [at 90° it is a flat
disc].
If one plots the volume of
the cylinder (y axis) vs fibre
angle ø (x axis), V will vary
following this curve, the
imaginary worm’s cylindrical
Shadwick R E J Exp Biol 2008;211:289-291
body remaining circular in
transverse section.
©2008 by The Company of Biologists Ltd
Continued next lecture