I wonder how long until we see some adult movies with this.

1989 - The Abyss

https://www.imdb.com/title/tt0096754/?ref_=nv_sr_srsg_0_tt_8...

How about 'Tentacle and Witches'?

There are so many Japanese anime about 触手 (Shokushu) which is also used to describe the whole mass of tentacles that a creature like an octopus has as opposed to an individual appendage.