Here are some helmetfish!  As part of my ongoing RPG enemy set (see the collection here: http://opengameart.org/content/side-on-pixel-art-rpg-enemy-sprites)  The initial idea was Ceninan's, and it's developed.  They might fit in a sunken castle, or perhaps in a particularly strange dream after too much sherbet.  Yeah!  There may be more of these sometime.  So far, I do generally plan to do a herring and a jellyfish.  If you have a suggestion, comment below.