Can the Fathomless’ tentacle be attacked?

I started playing a Lurker in the Deep Warlock, and have now updated it to a Fathomless Warlock due to the recent update. We came up to a situation where the tentacle was the only thing in attack range of someone, and our DM decided to have them attack the tentacle, at which point they asked me how that works. As far as I can tell there’s nothing describing what happens when it’s attacked/if it can be attacked. I assume a lot of this is up to the DM, but a lot of how the tentacle works is very vague in terms of it occupying physical space.