Editing Jellyfish (section)

=== Locomotion ===
[[File:Jellyfish locomotion.svg|thumb|upright=1.3|Jellyfish [[animal locomotion|locomotion]] is highly efficient. [[Muscle]]s in the jellylike bell contract, setting up a start [[vortex]] and propelling the animal. When the contraction ends, the bell recoils elastically, creating a stop vortex with no extra energy input.]]

Using the moon jelly ''[[Aurelia aurita]]'' as an example, jellyfish have been shown to be the most energy-efficient swimmers of all animals.<ref>{{cite web |url=https://arstechnica.com/science/2014/05/jellyfish-are-the-most-energy-efficient-swimmers-new-metric-confirms/ |title=Jellyfish are the most energy-efficient swimmers, new metric confirms |author=Rathi, Akshat |website=Ars Technica |access-date=3 December 2014 |date=15 May 2014 |url-status=live |archive-url=https://web.archive.org/web/20141103061826/http://arstechnica.com/science/2014/05/jellyfish-are-the-most-energy-efficient-swimmers-new-metric-confirms/|archive-date=3 November 2014}}</ref> They move through the water by radially expanding and contracting their bell-shaped bodies to push water behind them. They pause between the contraction and expansion phases to create two [[vortex]] rings. Muscles are used for the contraction of the body, which creates the first vortex and pushes the animal forward, but the mesoglea is so elastic that the expansion is powered exclusively by relaxing the bell, which releases the energy stored from the contraction. Meanwhile, the second vortex ring starts to spin faster, sucking water into the bell and pushing against the centre of the body, giving a secondary and "free" boost forward. The mechanism, called passive energy recapture, only works in relatively small jellyfish moving at low speeds, allowing the animal to travel 30 percent farther on each swimming cycle. Jellyfish achieved a 48 percent lower cost of transport (food and oxygen intake versus energy spent in movement) than other animals in similar studies. One reason for this is that most of the gelatinous tissue of the bell is inactive, using no energy during swimming.<ref>{{cite journal | last1=Gemmell | first1=B. J. | last2=Costello | first2=J. H. | last3=Colin | first3=S. P. | last4=Stewart | first4=C. J. | last5=Dabiri | first5=J. O. | last6=Tafti | first6=D. | last7=Priya | first7=S. |display-authors=3 | doi=10.1073/pnas.1306983110 | title=Passive energy recapture in jellyfish contributes to propulsive advantage over other metazoans | journal=Proceedings of the National Academy of Sciences | year=2013 | pmid= 24101461| pmc=3816424| volume=110 | issue=44 | pages=17904–17909| bibcode=2013PNAS..11017904G | doi-access=free }}</ref>