1. Jetting and vortices A canoe paddle pulled through still water on a lake trails small vortices behind, spinning off the paddle edges. Motion in fluid creates flow and a vortex is flow that spins. One kind of vortex is a toroid, i.e., doughnut- shaped. Vortices arise in air beside launched spores (Sphagnum), around beating bird and insect wings. Vortices arise in coffee when stirring mixes cream. Smokers blow smoke rings and cetaceans blow bubble rings: both toroidal vortices. There are crickets that communicate with air vortices. Taken from the web, this picture is of a vortex forming on the upstream side of a tidal turbine. Toroids may travel – expanding -- through the fluid or stay fixed (e.g., over a drain). songofthepaddle Remember that air is a fluid just as water. Vortices accompany jetting, and other kinds of locomotion through fluids Jetting through water as a means of locomotion involves vortices.

2. Fluids are difficult to compress/effectively incompressible, a fact which allows for translocation of forces by hydrostatic skeletons (worms). This same fluid property of incompressibility allows for changes of body shape hydraulically when fluids are actually displaced (tube feet). And if fluid incompressibility gets together with an opening its squeezing results in expulsion: jet propulsion (squids). Jet propulsion in dragonfly larve

3. Metamerism: serial repetition of body parts tagmata The segmented worms, Annelida, have a ‘modular’ body plan, segment after segment being much the same, repeated along the length of the body, with the same appendages; these modules function in locomotion by body waves (enabling localized changes in shape that relate to burrowing or swimming). And often in a species of annelid a subset of these metameres (segments) becomes modified and specialized to serve a common function. This specialized group of segments is referred to as a tagma. Insects are descended from metameric ancestors and have grouped their ancestral metameres into three body regions or tagma: head, thorax, abdomen. The head is the seat of sensory input (seeing, tasting etc.) and food handling: the head tagma functions in seeing, eating etc. Behind the head are three modules that have become (in flying insects) fused together to provide a firm platform against which leg and wing muscles can work: it is a kind of tagma of locomotion. The abdomen in contrast retains some telescoping mobility of its segments important in breathing and in the case of dragonfly nymphs in locomotion.

4. Potter wasp pedicel or petiole. Insect has two ‘necks’, one behind the head, and one between the thorax and abdomen: making both the abdomen and the head mobile relative to the thorax (the locomotory tagma). One might say there are 4 tagmata: thorax, head, abdomen and the petiole (a tagma of one segment). Torre- Bueno: “petiole: a stem or stalk; the slender segment between the thorax and abdomen in certain Diptera and many Hymenoptera; in the latter a pedicel formed of only one segment, or the first segment of a two-segmented pedicel in ants*; in plants the slender stalk of a leaf.” Petiole provides tagma manoeverability for stingingand immobilizing prey or for carrying prey (?). Hymenoptera pedicel Metamerism and the insect thorax as tagma (tagmata pl.) Head is a tagma: derived from segments combined in the course of evolution.

5. Source: Mill P.J. & Pickard R.S. 1975. Jet-propulsion in anisopteran dragonfly larvae. J. comp. Physiol. 97(4): 329-338 Some aquatic insects use jetting to escape and to breathe. Dragonfly nymphal/larval stage Ventilation and Locomotion are needs satisfied by the same system. Abdomen a tagma telescoping for changes in body volume.

6. Some dragonfly immatures (Order Odonata) jet water out of their rectum (posterior gut chamber) which is also a respiratory chamber. The insect uses a nozzle (see tapered terminal sclerites) to increase momentum (mass X velocity) and to aim the jet flow just as a squid siphon does. Telescoping in and out of abdominal segments changes abdomen volume and so haemocoel pressure which powers water intake and outflow; filaments filled with tracheae* project into rectum lumen for gas exchange. nozzle *Gas exchange in insects via tracheal system of air tubes.

7. Jetting used to ‘launch at prey’ or ‘escape when disturbed’ or ‘in water without a foothold’. Jet propulsion in insects is limited to dragonfly larvae; note this Mill & Pickard paper written with comparison in mind, e.g., to squids (Cephalopoda). Cycles of nymph jetting repeated at 2.2 per s for sustained progress; see Mill & Pickard’s longitudinal and oblique muscles diagram of 9 th and 10 th 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. 1975. Jet- propulsion in anisopteran dragonfly larvae. J. comp. Physiol. 97(4): 329-338.

8. 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 that trails behind on a fishing stem (stem transports nourishment by a shared coelenteron). Kevin Raskoff National Geographic Nectophore zooids in a hydrozoan Cnidarian

9. Tunicate: Urochordata Sea squirts are small barrel-shaped creatures often living in clusters. They have a ‘tadpole larva’ dispersal phase with a notochord, absent in adults. An incurrent siphon, see os above, brings seawater into a slitted pharynx which filters food; excurrent exits at ats. These two siphons have been adapted in some species for locomotion: see salps.

10. Peter J. Bryant “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” (Sutherland et al. 2010). Some tunicates called salps are Pelagic: living in the open ocean and swimming by ejecting seawater. See: Sutherland K.R., Madin L.P. 2010. Comparative jet wake structure and swimming performance of salps. J. exp. Biol. 213: 2967-2975.

11. Sutherland Fig. 3 “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 muscles contract, decreasing chamber volume 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”.

12. Assigned reading: Sutherland K.R., Madin L.P. 2010. Comparative jet wake structure and swimming performance of salps. J. exp. Biol. 213: 2967-2975. Kenneth Kopp Salp chains: individuals (zooids) strung together in colonies Colonial tunicates

13. Jellyfish Jetting locomotion Assigned reading: Dabiri J. O., Colin S.P., Costello J.H., Gharib, M. 2005. Flow patterns generated by oblate medusan jellyfish: field measurements and laboratory analyses. Journal of experimental Biology 208: 1257- in which they demonstrate the stopping vortex ring which contributes to medusa swimming. Yong, Ed 2013. Why a jellyfish is the ocean’s most efficient swimmer. Nature doi:10.1038/nature.2013.13895 JELLYFISH FORM AND FUNCTION Website by John H. Costello & Sean P. Colin, Roger Williams University. See this website for information about jellyfish swimming form from specialists: >fox.rwu.edu/jellies/index.html<

14. Medusae can be bullet-shaped (prolate) or plate-shaped (oblate). Velum has to do with directing the jet? Oblate medusae have smaller velums than prolate, contract more slowly when swimming and throw larger amounts of water behind them. Prolate Torpedo/bullet shaped More ‘streamlined’ oblate Swimming cycle: power stroke (contraction of subumbrellar circular muscles) followed by a recovery stroke (mesoglea returns its elastic force of distortion). Two vortex rings are formed in relation to this cycle.

15. Jetting by Jellyfish

16. Schematic of a jetting prolate medusa with vortex rings in the wake. Dabiri J O et al. J Exp Biol 2005;208:1257-1265 ©2005 by The Company of Biologists Ltd Jetting medusa with vortex rings in wake Periodic bell contractions decrease volume of subumbrellar cavity, displacing out the high bulk modulus (incompressible) water as a jet: jet propulsion. Swimming cycle: fluid efflux emerges during bell contraction: a toroidal volume of rotating fluid known as the power stroke starting vortex ring. This travels downstream – is shed -- behind the forward progress of the medusa. There are two things in the wake: this vortex and a central jet (D). The cycle continues with a second fluid efflux shed during bell relaxation and recovery, a recovery stroke stopping vortex ring as mesoglea returns its elastic force. of distortion, elastic force). Prolate drawn here is jetting other oblate is Rowing.

17. Kinematics of the starting, stopping and co-joined lateral vortex structures from Dabiri et al.. Dabiri J O et al. J Exp Biol 2005;208:1257-1265 ©2005 by The Company of Biologists Ltd Dye used to visualize the behaviour of the fluid in the wake of the swimming medusa. Starting vortex ring involves fluid originating from ‘regions inside the subumbrellar volume’, but also from outside the bell via ‘entrainment of ambient fluid’ [flow induced by vortex rotation]; motion of this ring is oriented at an angle away from the bell margin toward the central axis of the bell and downstream (broken arrows). ambient: surrounding solid arrows: direction of vortex rotation

18. Kinematics of the starting, stopping and co-joined lateral vortex structures. Stopping vortex ring: bell circular muscle fibres relax and bell opens (mesoglea returns energy for this that originated with the coronal muscle). This bell recoil makes a stopping vortex initially within the subumbrellar cavity. But fluid originating from outside the bell is also entrained: it is drawn toward the subumbrellar cavity.”

19. The quote below comes from Nature’s promotion blurb (Ed Yong) of contained articles (He is referring to Gemmell 2013). They “…contract their umbrella-shaped bells, [and] create two vortex rings – doughnuts of water that are continuously rolling into themselves. The creature sheds the first ring in its wake, propelling itself forward. As the bell relaxes, the second vortex ring rolls under it and starts to spin faster. This sucks in water which pushes up against the centre of the jellyfish and gives it a secondary boost...” I think this simplification helps understanding. The stopping vortex, which Dabiri et al. discovered, is created by the motion of the jellyfish through the fluid (just as the motion of a spore mass in sphagnum moss). In the case of the spores there is no expanding bell. The expansion of the bell in the jellyfish adds some complexity to how the stopping vortex is visualized.

20. Velella: By-the-wind sailor: using the wind for locomotion Wikkipedia from Meglitsch P.A. Invertebrate Zoology Wilson, E.O. 1975. Sociobiology. Harvard, Cambridge Mass. gastrozooid, gonozooid, dactylozooid, pneumatophore, etc. Colonial cnidarians create “a complex metazoan body by making organs out of individual organisms” (p 386, E.O. Wilson, Sociobiology)

21. Pneumatophore a zooid modified into a gas- filled float giving buoyancy to the colony below and also enabling sailing. Pneumatophore 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. They use stinging cells nematocysts to capture fish prey. Physalia: Portuguese Man ‘o War Sailing locomotion Fishing Stems trail