Seacucumber. They jizz at you when frightened.

The majestic manatee

Crinoids are pretty cool. https://www.youtube.com/watch?v=nlPtPEiNaeo . Comb jellies are pretty cool too. https://www.youtube.com/watch?v=sTFskdKVNs4

Maybe this is overly general, but I'm into marine mammals - whales, dolphins, seals, manatees, you name it...the baleen whales in particular are fascinating to me because they are so huge and can sustain themselves just on tons of tiny krill

Axolotl... cute and interesting... a walking fish who is just a salamander like amphibian... and heckin' cute.

vampire squid ez

I love octopus, chambered nautiluses and cuttle fish but I think jelly fish are my favorite. Nudibranchs are beautiful as well.

Kate Matsuda in scuba gear 😂

Mermaids.

Octopus

Turtle