BIO325H5 Lecture Notes - Lecture 8: Standard Gravity, Aurelia Aurita, Froude Number

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Published on 5 Feb 2019
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BIO325H5
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Lecture 8: Salps & Squid & Metamerism
January 30, 2019
Metamerism, Tagmata, Metamorphosis: annelids, arthropods, epitokes
Passive Energy Recapture in Jellyfish Contributes to Propulsive Advantage Over Other Metazoans
They may not look it but medusa are actually VERY efficient swimmers
Froude number coined “to compare propulsive performance of ships” when used to study
energetic efficiency- it’s misleading re diverse animals
A better measure that can be used to compare the energetic costs of locomotion between dissimilar
animals= cost of transport (COT)
o COT= Work/m X d X g
o [E= energy input to the system of mass, m, that is used to move the system a distance d, g,
is ‘standard gravitational acceleration 980 cm/s/s]
o COT= dimensionless
“By this measure, the moon jellyfish, Aurelia aurita, expends significantly less energy per unit of
wet mass per distance travelled than other animls
o Jellyfish swim with a low COT
o Are they good swimmers? Perhaps not, but they are very efficient
o Contribution of the stopping vortex is part of the reason jellyfish are so efficient
“A propulsive jet for locomotion is created by rhythmic compression of muscle bands encircling the
barrel-shaped body. Seawater enters pharynx via the [closable incurrent siphon] oral lips close and
circular muscle bands contract, decreasing the volume of the jet chamber [atrium] so that seawater is
accelerated out of the [now] posterior [excurrent] siphon [antagonists?]
“unique in possessing incurrent and excurrent siphons on opposite ends of the body allowing for
unidirectional flow and reverse swimming during escape” (Sutherland et al)
Vortex rings associated with jetting just as per jellyfish, but perhaps no opportunity here for ‘passive
energy recapture’?
Vortices are an important part of locomotion in fluids
- Sea squirts are sessile barrel-shaped creatures, often living
in clusters
- Through an incurrent siphon, see os (A)
- Beating cilia draw seawater into a large slitted pharynx
- Musuc sliding on the pharynx walls, filters out
‘microfoods’ such as diatoms, concentrating them in the gut
- The current exits the pharynx via gill slits into a
surrounding cavity called an atrium, leading to excurrent
siphon (ats)
- Some species of tunicate, called SALPS, have modified
this filter-feeding system for jetting
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Lecture 8: Salps & Squid & Metamerism
January 30, 2019
- In this hypothetical primitive mollusk
ancestor, the mantle [green] is a skirt-like
dorsal outgrowth of the main body
(visceral mass)
- It delimits a mantle cavity, bounded inside
by the body & containing the ctenidia (gills)
- The mantle secretes the calcareous shell
- The body forms of molluscs are diverse
- Snail (limpets) body form is considered more primitive- a
crawling foot topped by visceral mass
- A squid or cuttlefish or octopus represents very derived &
specialized body forms
- Jetting seawater from the mantle cavity via the
directable hyponome (funnel/nozzle) is combined
with ribbon fins at the functional posterior
(primitively dorsal) extremity
- The volume of the mantle cavity changes, and so does the
thickness of the mantle
- The mantle cavity expands & water intake occurs just behind
the head
- Then the mantle’s free anterior edge is buttoned to the side of
the visceral mass so that no water can pass
- Then the cavity decreases in volume expelling the
incompressible seawater out of the funnel
- Using anterioras a functional term for forward first attack
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Lecture 8: Salps & Squid & Metamerism
January 30, 2019
One way valves control intake of water into mantle cavity at sides
Pressure build up in seawater inside mantle cavity (circulars contract) forced the inner flaps of the
funnel against the mantle wall & water jets out of funnel (hypostome)
Funnel developed from posterior of primitive foot
Primitive ventral foot surface of ancestor became functional (going first) anterior end
Ribbon fins set up direct or retrograde waves, generating thrust forward/backward/spinning turn
o Varied fin shapes allow steering & stabilization
o Hyponome can be directed even for sudden lateral jumps
o Very agile pursuing predators, squids achieve greatest swimming speeds of any aquatic
invertebrate, up to 40 km/h
A swimming squid takes up & expels water by contracting radial & circular muscles in its boneless
mantle wall- elastic collagen ‘springs’ in the muscle increase the power of the jet
Beware potential confusion: squids jet-propel themselves & of course there is a fluid-filled cavity
involved= the mantle cavity
o The seawater in this cavity functions in locomotion by virtue of its high bulk modulus
o If the seawater were not incompressible, the jetting wouldn’t work
o But this cavity is not functioning as a hydrostatic skeleton antagonizing the mantle muscles
o Rather the mantle wall changes its own shape working as a muscular hydrostat
incorporating a collagenous fibre array
In the mantle several fibrous structures interact during jetting locomotion
o Cross collagen fibres make a tunic that prevents longitudinal dimension change*
o Radially running muscle fibres contract to thin the mantle wall
o Circular muscle fibres contract to thicken the wall
These circulars & radials are made antagonists by the tunic
The volume of the mantle wall as a muscular hydrostat must stay constant (just as if it were a
fluid-filled cavity) because ‘muscle is mostly water
The mantle can change in girth & thickness but because of the collagen ‘tunic’ it cannot get longer
in the mantle length dimension
** unlike the other helical tunics (tuber foot, nematode worms) this one cannot lengthen
- When the radial muscles of the mantle contracts, the volume of
the cavity is increased & seawater is drawn in
- When the circular muscles of the mantle contract, the volume of
the mantle cavity is decreased & 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)
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Document Summary

Perhaps not, but they are very efficient: contribution of the stopping vortex is part of the reason jellyfish are so efficient. Sea squirts are sessile barrel-shaped creatures, often living in clusters. Through an incurrent siphon, see os (a) Beating cilia draw seawater into a large slitted pharynx. Musuc sliding on the pharynx walls, filters out. Microfoods" such as diatoms, concentrating them in the gut. The current exits the pharynx via gill slits into a surrounding cavity called an atrium, leading to excurrent siphon (ats) Some species of tunicate, called salps, have modified this filter-feeding system for jetting. A propulsive jet for locomotion is created by rhythmic compression of muscle bands encircling the barrel-shaped body. Seawater enters pharynx via the [closable incurrent siphon] oral lips close and circular muscle bands contract, decreasing the volume of the jet chamber [atrium] so that seawater is accelerated out of the [now] posterior [excurrent] siphon [antagonists?]

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