1. 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

2. 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.
Jetting used to ‘strike at prey’ and ‘when disturbed’ or ‘in water without a foothold’.
Contrast jetting with ventilation: inspiration and expiration cycle of water intake and water egress, through cuticular ‘siphon’.
Jet propulsion in insects is limited to dragonfly larvae; note this Mill & Pickard paper written with comparison in mind, e.g., to cephalopods.
cycles of nymph jetting repeated at 2.2 per s for sustained progress; see their longitudinal and oblique muscles diagram of 9th and 10th abdominal segments.
“The effectiveness of the jet-propulsion mechanism is largely dependent upon a) velocity and mass of water ejected from the respiratory chamber b) the mass of the whole animal and c) magnitude of induced drag forces.” ‘cuticular restoring forces’
Mill P.J., Pickard R.S Jet-propulsion in anisopteran dragonfly larvae. J. comp. Physiol. 97(4):

3. Velella: By-the-wind sailor: using the wind for locomotion
Wilson, E.O Sociobiology. Harvard, Cambridge Mass.
Wikkipedia
These colonial cnidarians have created “a complex metazoan body by making organs out of individual organisms” (p 386, E.O. Wilson, Sociobiology)
from Meglitsch P.A. Invertebrate Zoology
gastrozooid, gonozooid, dactylozooid, pneumatophore, etc.

4. Sailing locomotion Fishing Stems trail
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.
Order Siphonophora (Cnidaria) are pelagic colonies of polypoid and medusoid individuals within the Class Hydrozoa, ~300 spp living in open ocean [pelagic]. (Hydrozoans are typically colonial, but those in other orders are sessile.) Moving in the water column near the surface of the sea they trail long ‘fishing stems’ with batteries of nematocysts catching small fish as prey.
Pneumatophore of the Portuguese Man ‘o War is a zooid modified into a gas-filled float giving buoyancy to the colony below and also enabling sailing by the surface winds.
Fishing
Stems
trail

5. 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

6. Tunicate: Urochordata
Barrington, E.J.W The Biology of Hemichordata and Protochordata. Oliver & Boyd, Edinburgh, London.
Scanned from Barrington, p. 84; os inhalant siphon, ats exhalant siphon. In B ic is the direction of the incurrent which moves out of the pharynx lumen through the pharynx slits into an atrial cavity, thence to the ats. The current is created by beating cilia. Sheets of mucus on the pharynx walls trap the diatoms and other tiny organisms that are then concentrated and passed on down the gut. This sessile filter feeder, the species is Clavelina lepadiformis, is an example of a more typical tunicate. Compare with the salps.
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.

7. 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
Pelagic: any water in a sea or lake that is neither close to the bottom or the shore (Wikki) ‘open ocean’
Peter J. Bryant

8. Salp chains: individuals (zooids) strung together in colonies
Colonial tunicates
I wonder if vortex-assisted locomotion (vortex-ring propulsion) is not universal in jetting animals?
Are there any fish that employ jet propulsion? Flounders (flatfish) use their ‘offside’ operculum. See Brainerd E.L., Page B.N., Fish F.E Opercular jetting during fast-starts by flatfishes. J. exp. Biol. 200:
Kenneth Kopp
Assigned reading:
Sutherland K.R., Madin L.P Comparative jet wake structure and swimming performance of salps. J. exp. Biol. 213:

9. Sutherland Fig. 3 Are there fish evolved to jet?
“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. Next, the 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”.
Are there fish
evolved to jet?

10. Chordata and the notochord as a hydrostatic. axial skeleton
Chordata and the notochord as a hydrostatic* axial skeleton *Kier mentions notochord under ‘Additional examples’
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.
“The notochord of ascidians [tunicates], cephalochordates, many larval and adult fish, and frog tadpoles... is considered to employ hydrostatic support.”
Also from Kier: “Although many hydrostatic skeletons include liquid-filled cavities, some may be partitioned by septa, which allows for independent operation of portions of a hydrostatic body or structure. Indeed, a range of relative hydrostatic fluid volume is observed, including muscular hydrostats...which lack fluid-filled internal spaces. Such an arrangement allows much more highly localized control of deformations, with the potential for much greater diversity and complexity of movement.”
***contrast with annelids: ventral solid nerve cord; anterior blood flow in dorsal vessel

11. Chordata, Subphylum Cephalochordata
myotome block separations
evident here just below dorsal ‘fin’
Morgan Mccomb
“These animals [cephalochordates] are so often used to illustrate the fundamental features of vertebrate organization that it is only too easy to forget that they are not vertebrates at all (Barrington 1965)”. His point is, they are not ‘little fish’. Adult amphioxus are benthic (bottom burrowing) filter feeders. Their notochord and axial musculature enables them to swim in the water column by retrograde undulatory body waves, ‘sort of like a fish’; their myotomes and notochord are however best not considered adapted for swimming: they use their metameric musculature for burrowing more than swimming.
Barrington E.J.W The Biology of the Hemichordata and Protochordata.
Oliver & Boyd, Edinburgh & London.

12. 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
There is a tail (the part beyond the anus). There is cephalization, but no neck. Tails and necks are body regions that may serve different functions in different animal species.

13. Assigned reading: Long, J. H. Jr. et al. 2002
Assigned reading: Long, J.H. Jr. et al The notochord of hagfish Myxine glutinosa: visco-elastic properties and mechanical functions during steady swimming. J. exp. Biol. 205:
“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.

14. Cell structure of notochord
Kardong
Connections of muscles to nerve cord recalls muscle tails of nematodes. Sheath of the notochord is comprised of collagen fibres.

15. 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 v-shaped myotomes run longitudinally (as is also the case with fish).
One way of describing notochord function: ‘it is a laterally flexible fixed-length skeletal element that makes the axial muscles on the right side of the body antagonists to those of the other side’. If no notochord and fibres on both sides contract simultaneously, the longitudinal dimension of the animal would shorten – head approach tail.

16. All quotes from older Kardong 2nd edition 1998 (Kardong 6th edition 2012, is on reserve) and must deal with notochord
“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]

17. 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
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

18. 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.
The BC is a rubber vest into which air can be introduced from the air tank – it swells, occupies more volume and reduces the diver’s density. It can be adjusted (air in/air out) until the diver stays steadily at depth, not rising or sinking. (Adding weights or removing them is an alternative way of changing your density.)
[Buoyancy compensators give buoyancy because they add only relatively little weight but when inflated they displace much more water.]

19. Buoyancy see Vogel Comparative Biomechanics p. 96
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

20. 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.
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.
Fisheries & Oceans Canada