Cephelapods are very nice to watch and always put a smile on my face, but what really gives me a huge sense of awe and wonderment on a dive is a free swimming salp. Did I ever mention that I think tunicates are mad?
example 1.
boring but amazing reading
Sea Squirt Regrows Entire Body from One Blood Vessel | LiveScience
example 2.
Short and beautiful films of salps
http://www.oceanfootage.com/video_clips/EK02_021
from
http://www.oceanfootage.com/stockfootage/Salp
Just a self replicating mobile digestive tract - the mother and father of us all. Has a spinal-chord as a baby, then settles down and re-absorbs it.
Wow!