I haven't seen this IMAX film but the creature(s) you are referring to are
undoubtedly siphonophores (order Siphonophora). These are colonial hydrozoans
(class Hydrozoa, which also contains the ubiquitous *Hydra*, and belong to the
phylum Cnidaria along with creatures such as corals, jellyfish and anemones).
They are common worldwide in epipelagic to mesopelagic waters (and deeper?).
Quoting gmark at svs.com:
> I recently saw an IMAX film about life in the deep sea, and
> it mentioned a creature (or cluster of creatures or something)
> that was the size of a football field. It was very, very deep, and
> some sort of collaborative collection of other creatures. It was
> called something like "cyphono-form" or "siphonaform" ro
>> Anyone recall?