Transcript Ensis directus

Jan 22 lecture
Odonate jetting
Body plan Mollusca
Bivalve foot in hydrostatic
burrowing
Slug floot walking on glue
Notochord as hydrostatic
axial skeleton
Freshwater insects that use jetting to escape and to breathe
Some dragonfly immatures (Order Odonata) can jet water out of their rectum,
the posterior chamber of their gut; they use funnel-shaped terminal sclerites
to aim flow just like a squid siphon; telescoping in and out of abdominal
segments powers water intake and outflow; filaments filled with tracheae
project into rectum lumen for gas exchange.
Raptorial labium of these
dragonflies modified to
apprehend prey: It is extended
suddenly and can grab other
small insects or even small
fish. Is it possible that jetting
plays a useful role in speeding
up this ambush attack?
See reserve
books for
general
anatomy of
different
molluscs
Rupert,Fox
Barnes 7th
or Brusca
A mollusc ancestral to squids, to see how foot shell &
mantle cavity changed during evolution
dorsal view
streamlining
Shell is an internal
remnant sunk within the
mantle tissue; it is
called the pen
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.) Read Kathyrn in detail but not Winter.
The foot end (anterior), the siphon end (posterior), the hinge dorsal
but the animal orients normally foot end down.
An interesting picture of razor clams packaged for sale in a chinatown
market in Philadelphia
Hydrostatic function of blood in haemocoel sinuses:
blood is travelling at low pressure in the foot through
indescriptly shaped spaces, making its way back to the
heart (pump).
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Biomimicry is a recently coined engineering term for building/designing
devices inspired by animal adaptation. (See Kathryn Knight.)
‘Self-burying machines’; Winter is an engineer at MIT: “There are many
applications that could benefit from a self-burrowing reversible anchor that
embeds efficiently...”
Winter’s interest in razor clam piqued by its burrowing ability: can go down
>3 times body length [very fast] ; this not consistent with muscle capacity.
These clams use a ‘TWO-ANCHOR SYSTEM’
One region of the animal’s body (foot) expands to form an anchor while
another body region contracts (i.e., valves pulled away from the surrounding
substrate; working from purchase, valves then foot then valves [like the
earthworm’s chaetae] clam can burrow down (or back up) by reshaping its
body hydrostatically.
But the razor clam does something that helps it to burrow better: it “uses its
valves to create a pocket of fluidized substrate [‘quicksand’] around its body
to reduce drag”.
When the valves are pulled back from the surrounding ‘soil’ (soil that is
water-saturated) “it sucks more water toward its body so you get increased
unpacking of the soil particles” and they won’t give support – and less
resistance to penetration of the foot. [Note!!! no incurrent siphon brings
down ocean water for this fluidization.]]
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Note: hinge and
Median line with down arrows
shells misleading re
shows route by which blood within razor clam
sinuses is displaced into foot,
anatomy
serving there a hydrostatic
function changing foot shape.
Pedal protractor muscles contract
to push foot out between the
hinge
valves by displacing fluid (blood)
in haemocoel visceral mass
sinuses into the foot
Valves either push out against the
surrounding substrate or not,
depending on the activity of the 2
adductor muscles (only one
shown); if the adductors are
relaxed the ligaments hold the
valves against the sand and mud
at the sides of the burrow.
Swollen foot expands and
anchors; retractors (black) draw
the animal down toward the
swollen foot through quicksanded
soil.
but diagram
illustrates
muscle effects
on visceral
mass and foot
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from Winter’s discussion: (fluid mechanics jargon, very difficult for a
biologist to follow and one might be wondering exactly what he means by
‘soil’; I keep thinking of sand)
As E. directus contracts its valves [my underline], it reduces the level of
stress acting between the valves and the surrounding soil. [ Stress is good,
but no biologist would be talking about contracting valves: the shells
obviously don’t ‘contract’: he means 2 valves are pulled together by the
adductor muscles inside.] At some stress level, the imbalance between
horizontal and vertical stress causes the soil adjacent to the animal to fail.
[This is when the soil and water mix takes on a soupy consistency that won’t
support anything, i.e., ‘quicksand’.] Continued valve contraction draws pore
water towards the animal, which mixes with the failed soil to create a
region of localized fluidization [my boldface emphasis]”.
“...the clam fluidized the [immediately] surrounding soil (fluidize, i.e., you
could pour it) which dramatically reduced the drag on the shell, allowing the
mollusc to pull itself down -- before the surrounding sand particles slid back
into place and the soil resolidified. The energy required to move through the
fluidized substrate was a fraction of that required to move through it in its
nomal solid state.
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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)
Ensis directus burrowing motions.
Ensis directus burrowing motions. The dashed line indicates the depth datum.
White arrows denote valve and foot motions. Panels are snapshots of live E.
directus performing burrowing motions. The red silhouette denotes valve
geometry in the expanded state, before contraction. (A) Start of burrowing cycle.
(B) Foot extends downward. (C) E. directus pushes on foot, causing upstroke of
valves. (D) Valve contraction, which pushes blood into the foot, inflating it to form
a terminal anchor. (E) Contraction of the foot, which draws valves downward. (F)
Expansion of the valves, at the start of the next burrowing cycle.
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Forms of the many species of burrowing
bivalves will be greatly affected by the
great variety of soils (‘soil’ is a term here
embracing complexities of clay, sand,
organic matter etc.) in which they
locomote – moving up to filter feed per
the tide, down to avoid predation. The
razor clam is unusually narrowed. Why
this shape? Does it help it to achieve
speed in burrowing that enables it to outdig predators? What about the diversity
of ridges and shell texturings on
burrowing bivalves: could they be
functional in gaining purchase?
Geoduck (upside down)
valves 15-20 cm long.
Siphons up to 1 m long
Siphons incurrent and excurrent so
long they can’t be withdrawn in
between the valves any more..
Siphons evolve as pinched
off and produced regions of
posterior mantle
Some siphon diversity: different
lengths in different species.
Soft shell clam Mya arenaria (above).
Bivalves are typically filter feeders in
tidal zones, burrowing down between
tides; phytoplankton filtered from water
entering via incurrent siphon. Filtering
of food by gills
Christopher Taylor
From Class Bivalvia 20000 species in 75 families, we go
to Class Gastropoda, 35000 species.
Pulmonates are a subclass of gastropoda and include land snails
name is from the conversion of mantle cavity into a lung
Gastropods
move on their
foot using
“muscular
waves moving
along [its]
ventral
surface”
“the force of these waves
is coupled to the substratum
by a thin layer of pedal
mucus” Denny 1980
There are monotaxic and ditaxic gastropod species
Pedal locomotion in Pulmonates
Mantle cavity of pulmonates has been converted into a
lung: hence ‘pulmonate snails’ of which slugs are just one
sort; edges of mantle cavity seal to back except for
pneumostome opening; roof of mantle cavity
vascularized, no gill..
From Wikimedia Commons
Arion ater, black slug
Pacific Banana Slug
pneumostome: entry to lung
See video of pedal waves http://www.flickr.com/photos/turtblu/3424848753
Long, J.H. Jr. et al. 2002. The notochord of hagfish Myxine glutinosa:
visco-elastic properties and mechanical functions during steady
swimming. J. exp. Biol. 205: 3819-3831.
• “Chordates have evolved an unique hydrostatic axial skeleton, the
notochord, that is present in all taxa of that phylum early in
development; it is retained in the adults of some taxa and modified
by vertebral elements in others... Notochords are hypothesized to
have evolved to stiffen the body (Goodrich, 1930) and to prevent
body compression during muscle activation (Clark, 1964). In
addition, notochords may adjust function by means of dynamically
variable mechanical properties (Long et al., 1998).
Long, J.H. Jr. et al. 2002. The notochord of hagfish Myxine glutinosa:
visco-elastic properties and mechanical functions during steady
swimming. J. exp. Biol. 205: 3819-3831.
• “Chordates have evolved an unique hydrostatic axial skeleton, the
notochord, that is present in all taxa of that phylum early in
development; it is retained in the adults of some taxa and modified
by vertebral elements in others... Notochords are hypothesized to
have evolved to stiffen the body (Goodrich, 1930) and to prevent
body compression during muscle activation (Clark, 1964). In
addition, notochords may adjust function by means of dynamically
variable mechanical properties (Long et al., 1998).
Anatomy of a chordate
An animal having a notochord and metameric axial musculature making body waves.