In English, you usually don't want to be compared to marine life. "Cold fish," "shark" and "whale" are not often intended as compliments, and "come out of your shell" is commonly addressed to the anti-social.
Japanese have a somewhat different take on the undersea world. In a landmark 1959 TV drama, actor Frankie Sakai expressed a heartfelt desire to escape the pain of being human with the famous line "Watashi wa kai ni naritai" ("I want to be a shellfish").
The professor hero of Yoshifumi Tsubota's portentous, gorgeous "The Shell Collector" ("Sheru Korekuta"), which premiered at this year's Rotterdam international film festival, collects shells instead of trying to squeeze himself into one, but he is also escaping something.