Skip to main content

Free Content Jet Propulsion and the Evolution of the Cephalopods

Download Article:
(PDF 3661.791015625 kb)
The first cephalopods, recognized as such by their possession of a chambered shell with a siphuncle, appeared in the late Cambrian. They are assumed to have been crawling animals. Lightening the shell, made possible by ion and water removal and the consequent appearance of gas in the chambers would have allowed the animal to escape upwards, using the jet resulting from a sudden withdrawal of the body into the shell. Nautilus still produces a propulsive jet in this manner. It can also generate a low pressure stream using the wings of the funnel to waft a flow through the gills. It is argued that all the other ectocochleates would have had propulsive mechanisms based on one or other (or both) of the means by which Nautilus develops a jet. One consequence of this conclusion is that none of them were powerful swimmers. The momentum imparted by a jet depends upon the ejected mass multiplied by the velocity of the jet. But E = ½mv2 so that while slow speed propulsion using the ventilation stream can result in a very low cost of transport any attempt to achieve high speeds is very costly. Only marginal improvements could be made by lightening or streamlining the shell. More economical fast locomotion could only be achieved by increasing the volume of the mantle cavity, and this meant scrapping or internalizing the shell. It also necessitated the development of a new set of propulsive muscles, in the wall of the mantle. Mantle musculature now took on both locomotor and ventilatory functions. The two functions have incompatible requirements; for efficient jet propulsion the stream volume should be maximized, while efficient oxygen uptake should minimize the flow. Octopods have optimized oxygen extraction, the squids, in general are specialized for jet propulsion. In the teuthoids and octopods progressive shell reduction also led to the loss of neutral buoyancy, regained in some forms by ion-substitution in the tissues and an associated return to relatively slow-moving lifestyles. Jet propulsion remained an extravagant form of propulsion at all but the slowest speeds. Many coleoids, as a result, have moved on to develop yet another locomotor system, replacing jet propulsion by undulant fins.

14 References.

No Supplementary Data.
No Data/Media
No Metrics

Document Type: Research Article

Publication date: 1991-09-01

More about this publication?
  • The Bulletin of Marine Science is dedicated to the dissemination of high quality research from the world's oceans. All aspects of marine science are treated by the Bulletin of Marine Science, including papers in marine biology, biological oceanography, fisheries, marine affairs, applied marine physics, marine geology and geophysics, marine and atmospheric chemistry, and meteorology and physical oceanography.
  • Editorial Board
  • Information for Authors
  • Subscribe to this Title
  • Terms & Conditions
  • Ingenta Connect is not responsible for the content or availability of external websites
  • Access Key
  • Free content
  • Partial Free content
  • New content
  • Open access content
  • Partial Open access content
  • Subscribed content
  • Partial Subscribed content
  • Free trial content
Cookie Policy
Cookie Policy
Ingenta Connect website makes use of cookies so as to keep track of data that you have filled in. I am Happy with this Find out more