Re: What is the process squid use when swim by using their siphons as jets?

Watching a squid swim by jet propulsion is fascinating.

And it's really quite easy for the squid to do, as well as explain!

It's easiest to think of a squid in two parts - the first part (head and 
tentacles) has a "mantle" around the top of it, where the fins are. The 
mantle can expand and contract and in doing so, can suck in water, and 
then force it through the siphon - creating jet propulsion.

So to propel itself through the water, the squid must:

(1) Expand the mantle to take water onboard, then lock it SHUT.
(2) Contract the mantle (using special giant neurons to convey message)
(3) Expel the water resulting from the contraction through the siphon
(4) Direct the siphon
(5) Swim!

The muscle contractions required to initiate this behaviour are controlled 
by "giant neurons", which are large enough to 

Check out http://seawifs.gsfc.nasa.gov/OCEAN_PLANET/HTML/squid_move.html 
for a cool video of a squid using jet propulsion.