Lecture 9 Bio 325
Jetting in jellyfish, scallops, squids leads on to:
Jetting propulsion in Arthropoda, Odonata: whichfunctions also with gas
exchange.
Jetting propulsion in colonial Hydrozoa involves nectophores.
Jetting propulsion by salps: tunicates in chains.
Notochord as muscular hydrostat
Buoyancy
Freshwater insects that use jetting to escape and to breathe.
Some dragonfly immatures (Order Odonata) jet water out of their rectum, the posterior
chamber of their gut which is also a respiratory chamber; they use nozzle-shaped (tapered)
terminal sclerites to increase momentum (mass X velocity) and to aim flow just like a squid
siphon; telescoping in and out of abdominal segments + haemocoel pressure powers water
intake and outflow; filaments filled with tracheae project into rectum lumen for gas exchange.
Mill P.J., Pickard R.S. 1975. Jetpropulsion in anisopteran dragonfly
larvae. J. comp. Physiol. 97(4): 329-338.
Velella: By-the-wind
sailor: using the
wind for locomotion
Wilson, E.O. 1975. Sociobiology. Harvard, Cambridge Mass.
Wikkipedia
from Meglitsch P.A. Invertebrate Zoology
gastrozooid, gonozooid, dactylozooid,
pneumatophore, etc.
Physalia: Portuguese Man ‘o War
Sailing
locomotion
Pneumatophore
They use stinging cells
nematocysts
to capture fish prey.
Zooids: nectophores:
squirt out jets of seawater
to propel the colony.
gastrozooids are sac-like,
specialized for ingestion
and distribution of
nutrients to rest of colony
dactylozooids with
batteries of nematocysts
etc.
Fishing
Stems
trail
Nectophore zooids in a hydrozoan Cnidarian
A colony of zooids: at one end specialized as swimming individuals
called nectophores, also called swimming bells. They jet seawater out
of their subumbrellar openings, moving the colony, trailing behind on
a fishing stem (stem transports nourishment by a shared coelenteron)
about in the water column, presumably in a co-ordinated fashion.
National Geographic
Kevin Raskoff
Tunicate: Urochordata
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Sea squirts are small barrel-shaped creatures often in clusters. They have a ‘tadpole larva’
dispersal phase that has a notochord (one of the reasons to classify them as Chordata), but it
is not present in adults. An incurrent siphon, see terminal os above, brings seawater into a
slitted pharynx which filters food; excurrent exits at ats through 2nd siphon.
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Salp: semitransparent cylindrical free-swimming tunicate : Cyclosalpa affinis.
Phylum Chordata, Subphylum Vertebrata. Another chordate subphylum is
Cephalochordata (amphioxus/Branchiostoma).
Phylum Chordata, Subphylum Urochordata: Tunicates are sessile ‘sea squirts’ with a
tadpole larval dispersal stage: characterized by 1) notochord 2) dorsal hollow nerve cord
3) pharyngeal clefts related to filter feeding. Some tunicates are pelagic: salps.
“A propulsive jet for locomotion is created by rhythmic compression of muscle bands
encircling the barrel-shaped body. Fluid enters the anterior oral siphon to fill the mostly
hollow body of the salp. ...oral lips close and circular muscle bands contract, decreasing the
volume of the jet chamber so that fluid is accelerated out of the posterior atrial siphon.”
[antagonists?] “...unique in possessing incurrent and excurrent siphons on opposite ends of
the body allowing for unidirectional flow and reverse swimming during escape”.
Pelagic
Peter J. Bryant
Salp chains:
individuals (zooids)
strung together in
colonies
Colonial tunicates
Kenneth Kopp
Assigned reading:
Sutherland K.R., Madin L.P. 2010. Comparative jet wake structure and swimming
performance of salps. J. exp. Biol. 213: 2967-2975.
Sutherland
Fig. 3
In situ jet wake structures made visible with fluorescein dye.
Are there fish
evolved to jet?
Sutherland K R , and Madin L P J Exp Biol 2010;213:29672975
©2010 by The Company of Biologists Ltd
Chordata and the notochord as a hydrostatic* axial skeleton
*Kier mentions notochord under ‘Additional examples’
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5.
6.
Name of the phylum – Chordata** -- comes from notochord; chordates are
diagnosed by certain body features shared by all species in the phylum:
pharyngeal gill slits: a perforated pharynx
dorsal tubular (hollow) nerve cord (dorsal to the digestive tract)***
tail, body continues postanal (anus is not terminal)
circulation occurs from the heart forward in a ventral vessel and then up around
the pharynx and rearward in a dorsal vessel***
jointed endoskeleton
--- and at some time in their development all chordates have a notochord, a long
cylindrical tube bounded by helical connective tissue fibres. surrounding a core of
cells and fluid; this is also functioning as a hydrostatic structure.
***contrast with annelids: ventral solid nerve cord; anterior blood flow in dorsal vessel
Chordata, Subphylum Cephalochordata
myotome block separations
evident here just below dorsal ‘fin’
Morgan Mccomb
Barrington E.J.W. 1965. The Biology of the Hemichordata and Protochordata.
Oliver & Boyd, Edinburgh & London.
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There are ‘fins’, very different than the mobile
bone-reinforced fins of fishes.
A pair of metapleural folds run ventrally, right
and left, back to the atriopore (this being a
separate excurrent exit for filtered seawater*).
These longitudinally alligned structures should
lend stability against shear forces involved in
rolling (canoes without keels are liable to roll).
The notochord is located just below the nerve
chord, an intimate structural relationship
because the the nervous system co-ordinates
body side-to-side bending via the notochord.
* Filter feeding is accomplished by the slitted
pharynx with micro-organisms separated from
an incurrent created by beating cilia..
IASZoology.com
Romer
Assigned reading: 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.
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“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).
Notochord is another example of a hydrostat, and given that it involves muscle,
perhaps it is reasonable to think of it as a muscular hydrostat.
Cell structure of
notochord
Kardong
• Muscles of amphioxus are arranged
in a series of V-shaped blocks known
as myotomes, separated by sheets of
connective tissue, myocommas.
Because they are v-shaped several
appear in any single transverse
section.
• The muscle fibres within these vshaped myotomes run longitudinally
(as is also the case with fish).
All quotes from older Kardong 2nd edition 1998
(Kardong 6th edition 2012, is on reserve) and must deal with notochord
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“Such mechanical structures, in which the outer wall encloses a fluid core, are
called hydrostatic organs.”
“The notochord is a hydrostatic organ with elastic properties that resist axial
compression.”
Kardong does an ‘IMAGINE IT AS IT ISN’T’
“To understand the notochord’s mechanics, imagine what would occur if one block
of muscle contracted on one side of an animal without a notochord. As the
muscle shortens it shortens the body wall of which it is a part and telescopes the
body [animal collapses longitudinally like an accordion] . In a body with a
notochord, the longitudinally incompressible cord resists the tendency of a
contracting muscle to shorten the body. Instead of shortening the body, the
contraction of the muscle sweeps the tail to the side.” That is, the notochord
functions to enable undulatory (rear-directed, i.e., retrograde, body waves).
[plastic ruler illustration]
Summarizing the working and functions of the notochord: it is not just
a simple fluid-filled chamber surrounded by connective tissue acting to
translocate muscle forces
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It is a hydrostat and at least in part a muscular hydrostat -- because a tunic of
helical connective tissue fibres works against muscle and fluid within.
It stiffens the body longitudinally, preventing it from shortening when axial
muscles contract.
It makes the longitudinally alligned muscle fibres of the right and left sides
antagonists.
It promotes lateral (transverse) body bending, which is the basis of undulatory
body waves.
Since it is composed in part of muscle cells (capable of contracting) there is a
dynamic quality to its function as a skeleton: it can change its stiffness
topographically to facilitate adaptive bending
Buoyancy
• Density is mass per unit volume; so regulating your density is
a matter of losing weight or increasing your volume. Some
swimming animals regulate body density.
• You soon realize as a scuba diver that swimming is much
easier when you are not working to stay down or to keep from
sinking, when you are neutrally buoyant.
• A diver achieves neutral buoyancy by regulating body density
with a buoyancy compensator (BC). Bony fishes do the same
thing.
Buoyancy see Vogel Comparative Biomechanics p. 96
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Archimedes’ Law : objects heavier than the volume of water they displace will sink;
objects lighter than the volume of water they displace will rise. A fish is buoyed up by
a force equal to the weight of the water it displaces. It can change this force by
changing its volume, i.e., displacing more or less water. Secreting oxygen gas into its
swim bladder from the blood, the fish increases its volume and displaces more water,
so increasing the force acting to make it rise in the water column. Conversely it can
absorb oxygen gas from the bladder and so sink.
Inland fishes of NY, Cornell
Swim bladder /Gas bladder
Many bony fishes have a single median gas bag in their body used to change their density, giving
neutral buoyancy at different levels in the water column. This bladder, situated just below the
backbone and just above the viscera, contains oxygen at a high concentration; the oxygen is
actively secreted from the blood.
Fisheries & Oceans Canada
Ancestors of bony
fishes, living in fresh
water, evolved lungs
to supplement their
gills in times of
drought. When some
of these ancestors
reinvaded the seas
these lungs evolved
into swim bladders.