Lect6Jan20

Report
Serendipity: the faculty of making happy and unexpected discoveries by
accident
• Roberts T.J., Azizi E. 2011. Flexible mechanisms: the diverse roles of
biological springs in vertebrate movement. J. experimental Biology 214:
353-361.
The commonest device that confers motility in animals is
muscle.
But there are some oddities in how animal movement can be achieved:
erection of antennal hairs in mosquitoes occurs by hydration.
Some plants achieve
motility by hydration,
e.g., Mimosa: the
imbibition of water -and its an aspect of
their growth.
The hairs on the
antenna of a mosquito
start out lying flat
against the antennal
axis: recumbent.
An annular pad of
protein near the base of
each hair absorbs water
and causes the hair to
swing normal (erect)to
the axis of the antenna
Vogel, Life’s Devices p. 256
Pecten, scallop: water-jet swimming propulsion
Seawater exits from 2 openings near the hinge as the valves are adducted: this jets the
scallop forward.
Water jetting as a means of locomotion: dragonfly nymph (immature):
jet out water from last chamber of gut, rectum
locomotion combined with irrigation of rectal gills for gas exchange
Muscular hydrostats
Definition: a skeletal system of body or body
appendage movement that relies upon the
incompressibility of muscle itself, i.e., there is no
fluid-filled cavity. Muscle is mostly water and it is a
tissue that can change its shape and this permits it
to achieve changes in body shape by virtue of its
relative incompressibility.
Muscular hydrostat
• Definition: a skeletal system of body or body appendage movement that
relies upon the incompressibility of muscle itself, i.e., there is no fluidfilled cavity to translocate forces. So the muscle itself does the
translocation.
• Muscle is mostly water and it is a tissue that can change its shape and this
permits it to achieve changes in body shape by virtue of its relative
incompressibility.
Gosline J.M., & Demont M.E. 1984. Jetpropelled swimming in squids. Scientific
American 252: 96-103.
http://vimeo.com/5879164
Comment videos online
The seawater within the mantle cavity of the squid is not
functioning as a hydrostatic skeleton. But it is the basis of the
animal's jet propulsion, which in turn depends upon the
incompressibility of seawater. When the radial muscles of the
mantle contract, the volume of the mantle cavity is increased
and seawater is drawn in. When the circular muscles of the
mantle contract, the volume of the mantle cavity is decreased
and seawater is squirted out. The action-force of the jetted
seawater creates a reaction force that pushes the squid in the
opposite direction: opposite to whatever direction the funnel is
pointing.
Valves control intake of
water into mantle cavity at
sides .
Pressure build up in
seawater inside mantle
cavity (circulars contract)
forces the inner flaps of the
funnel against the mantle
wall
Three structures interact: 1) collagen fibres (connective tissue) make a tunic that
prevents longitudinal dimension change 2) radial muscles contract to thin the mantle
wall and 3) circular muscles of the mantle contract to thicken the wall.
Circulars and radials are antagonists.
The mantle is a muscular hydrostat and its volume must stay constant (just as if it were
a fluid-filled cavity).
Because of the collagen ‘tunic’ the mantle cannot get longer in the A to B dimension:
but it can change in girth.
A
B
Mantle
wall
Internal
organs
1.
2.
Escape Jet
Cycle of
squid
relaxed
contracted
relaxed
Radial muscles contract to cause:
hyperinflation: seawater intake into
mantle cavity: outside diameter of mantle
increases by approximately 10% over
resting diameter (girth increase); cavity
volume increases 22% re relaxed volume,
wall thins.
Circular muscles contract to bring mantle
to about 75% of its relaxed diameter,
radials restored to precontracted length
(girth decrease): volume drops &
pressure rises sharply , forcing the inlet
valvesl against the mantle wall and
leaving only the funnel as exit.
• The mantle wall can function as a muscular hydrostat -- a fluid skeleton
without a distinct fluid chamber -- that makes antagonists of the radial
and circular muscles: contraction of one kind of muscle restores the other
to its relaxed state via this type of fluid skeleton. The radial and circular
muscles become coupled as antagonists by virtue of their own tissue being
significantly water and so incompressible – and because the mantle
cannot lengthen. Because the mantle is incompressible it must retain an
overall constant volume; and it cannot get longer as mantle muscles
contract because of the collagen fibre tunic that prevents any movement
in that direction. Thus, it can only increase or decrease in thickness – at
the same time changing its overall diameter and the capacity of the
mantle cavity. When the radials contract the mantle walls must get thinner
and the walls move apart -- to maintain hydrostat volume. Conversely
when the circulars contract the mantle wall must get thicker as the overall
outside diameter of the mantle decreases. If there were no inextensible
fibres, if the animal’s mantle was not in a jacket of fibres preventing it
from lengthening, then the radials and the circulars could not have an
antagonistic effect on each other.
Echinodermata tube feet/podia
• Calcareous plates in dermis Ca Carbonate ‘ossicles’
• Water vascular system: tubes: ring canal and radial canal, filled with
coelomic fluid, amoebocytes
• Ambulacral groove tube feet, distal extremity is a disc stiffened internally
by small ossicles: rosette, epithelium: mucus-secreting cells, disc muscles
create partial vacuum, disc acts like a suction cup, adhere to valve of
bivalve prey
• Ampulla: fluid reservoir with ampullar muscles; spiral connective tissue in
podium wall enables protraction
• Lateral canal: tiny one-way valve eliminates backflow when ampullar
muscles contract
• Retractor muscles, postural muscles; podia push animal forward
Taken from
Brown, F.A.
Selected
Invertebrate
Types, p. 521
Branchiostoma
amphixous

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