If they live deep underwater, then they will probably never develop legs. So far they only use their fins for better movement. But if there are constant low tides, then they may adapt. Albeit in a couple million years.
Happy early birthday. It’s still cold, dead winter in my city, =/ Anyways, I’m not a movie person but “To All the Boys I’ve Love Before” seems popular. Oh, you should try “The Hate U Give” movie if you liked the book. ;)