What I always wanted to know about tentacles

why is it that underseas there is such a rich fauna of tentacular animals while none cruises the upper crust? Is the lower gravity effect enough to make life grow inumerous arms? squid octopus jellyfish anemonaes and us up here with only 2 arms at the most... (some monkeys are said to have 4 hands, but that leaves them with no feet)
I understand you would not be able to walk on tentacles ( no hard bits, like bone, to help stand upright against gravity's compression) but as arms??? Arms can be soft and need only to sustain what they want to hold.
The elephant's proboscis comes close to be a tentacle, but it's also a nose, and he has only one. Having two -or more- would have provided him with hands almost... what would he have done with them?
oh i'd like to know, i'd like to know
would they kiss under mistletoe?...