Deep Sea

[B Gilmour]

During a recent private e-mail discussion regarding mammalian sleep and its
evolutionary percurser, circadian rythms, it was asked whether deep sea
creatures still experience any dormant state akin to sleep, and does it
still fall into a 24 hr cycle. Deep sea represents a 24hr homogeneous
environment with no clues (visual or otherwise) to discern the differences
between nocturnal to diurnal.
Any expertise out their would be appreciated.
Thanks
gilmour at interlynx.net