either short "i" or long "i" for limascine.

And that'd be the first i that's either long or short. The second one seems to always be like ee so your lima bean rhyme will work just fine. My dictionary spells it without the s, thusly: limacine.

BTW, if you're at all interested in people understanding what you mean and don't have some nice explanatory context, you might consider, rather than using limacine, use slug-like. It doesn't rhyme with lima bean but.