Octopuses & relatives
Locomotion: Jet Propulsion
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The process of jet propulsion in an octopus is presented in simplified form in Figs. 1 - 2. The process is the same whether the animal is simply ventilating its ctenidia (gills) for gas exchange or whether it is jetting. There are two mantle openings, separated by the siphon. The openings are closed by flapper valves that pop into place during exhalation, thus forcing all the water out the siphon.  Correct alignment of the two mantle-cavity openings (Fig. 3) in relation to the siphon is ensured by symmetrically placed cartilaginous locking devices, termed here flapper valves.  Correct alignment ensures that the two flapper valves open and close without back-flow leakage during exhalation (Fig. 4). On entry into the mantle cavity the two flows irrigate the paired ctenidia , and then before exiting the now single flow picks up fecal discharge from the anus, urine from the nephridiopores, and ink from the ink sac.  Massive contraction of mantle musculature creates a propulsive jet from the siphon, that can be oriented in any direction.

Fig. 1.  Water intake
Fig. 2.  Water jets out on exhalation
Fig. 3.  Right-side opening into the mantle cavity of Enteroctopus dolfleini
Fig. 4.  Zip-loc configuration of one side of the mantle opening in a giant squid Onykia robusta.  The left side of the mantle is at the top of the photo, while the soft edge of the flapper valve is at the bottom
   

Research Study 1

Fig. 1.  Pelagic squid Doryteuthis opalescens
Courtesy NOAA, Federal Government, Washington
Fig. 2.  Muscle arrays in the mantle wall of Doryteuthis opalescens

Water flow through a squid functions both for gas exchange and jetting locomotion.  Studies on the pelagic squid Doryteuthis opalescens (Fig. 1) at the University of British Columbia indicate a different pattern for each function.  During escape jetting, for example, there are three phases: 1) filling of the mantle cavity powered largely by elastic recoil of the mantle wall from the previous jetting, with a small contribution from the radial muscles, 2) hyperinflation of the mantle cavity through contraction of radial muscles drawing more water in, and 3) expulsion of the water powered by contraction of circular muscles.  Hyperinflation serves to fill the mantle cavity maximally, making the jet more powerful.  In comparison, the more gentle pulsation of gas exchange is done in two ways, either by radial-muscle power or circular-muscle power, but both being antagonised by mantle tissue elasticity (Fig. 2).  The study emphasises the important role played by storage of elastic energy in the connective tissue-fibers of the mantle wall in both locomotion and gas exchange (for accounts of temperature-compensation effects and prey-capture experience on escape jetting in squids Doryteuthis opalescens see Neumeister, 2000 and Preuss & Gilly, 2000).

Gosline et al.   1983   J Exp Biol 104: 97
Neumeister et al.   2000   J Exp Biol 203: 54
Preuss & Gilly   2000   J Exp Biol 203: 559
An octopus Enteroctopus dolfleini ventilates its mantle cavity to enable gas exchange. The siphon, which in this view is pointing to the octopus' right, can be moved in any direction, most notably frontwards for backwards jet propulsion.  Note the expansion in volume of the mantle cavity during inhalation, the flapper vales closing on exhalation, and the used water being directed away from the body to minimise cross-contamination of clean incoming water with feces/urine/CO2-bearing outgoing water
   
A moribund Humboldt squid Dosidicus gigas jetting once gently, then culminating in a larger expulsion that douses the video camera and causes great confusion
   

Research Study 2

Fig. 1.  Comparative cost of swimming in squids and salmon
Fig. 2.  Note that despite their clunky appendage structure, unfavourable surface-area to volume relationship, and general lack of streamlining, several small crustaceans swim as efficiently as various squid species including Doryteuthis (Loligo) opalescens

Squids locomote by a combination of finning and jetting, and open-water species can maintain a pace of 1 - 2km • h-1 for weeks at a time.  During fast jetting the fins are rolled up to reduce drag.  How does the jet-propulsion swimming of a squid compare with tail-wagging swimming of a fish?  Acually, not well.  A squid uses over three times as much energy to travel half as fast as a sockeye salmon of comparable size (Fig. 1).  Fig. 2  shows the net cost of transport for various tail-wagging fishes, including sockeye salmon, in comparison with several species of planktonic crustaceans and three species of squids. The authors note the one advantage of squids over fishes in this regard is that the jet system automatically increases water flow over the ctenidia as swimming speed increases. Fishes expend increasing amounts of energy to ventilate their gills with increased velocity. 

O'Dor & Webber   1986   Can J Zool 64; 1591
O'Dor   1982   Can J Fish Aquat Sci 39: 580

Research Study 3

Fig. 1.  Enteroctopus dolfleini in full jetting flight backwards (Leftwards in the photo). The siphon is partly collapsed at the end of a jet cycle, and the mantle openings will soon open with a new intake of water. Note that the octopus has rolled its eyes backwards in an attempt to see where it is going

Jetting is used by octopuses (Fig. 1) not just for escape locomotion, but also for cleaning out potential homes, digging clams from sand, and chasing fishes away from prey remains.

Mather & Anderson   1999   J Comp Psychol 113: 333
A small octopus, either Octopus rubescens or Enteroctopus dolfleini, attempts to get away from being held by a SCUBA-diver.  Note that the diver has bare hands, quite confident that the octopus, despite its excited escape behaviour, will not bite with its beak
   

Research Study 4

Research at the Monterey Bay Aquarium Research Institute at Moss Landing, California and in situ video recordings in Monterey Bay with the ROV Ventana show that squids Doryteuthis opalescens of 10 - 120mm mantle length swim at an average velocity of 0.2m • sec-1 with burst speeds up to 1.6m • sec-1. The authors provide a variety of morphometric measurements that allow handy identification of size of squids from the ROV video recordings.  For example, a linear regression can predict dorsal mantle length (ML in mm) from a dimensionless ratio of mantle length over eye diameter taken from video records. 

CLICK HERE to a selection of video clips of various swimming squids, octopuses, and cuttlefishes provided by the Monterey Bay Aquarium, California and hosted by YouTube

Zeidberg & Robinson   2004   J Exp Biol 207: 4195