The Jellyfish emoji is missing from the unicode specification, I have on multiple occasions, wanted to send a Jellyfish emoji to somebody, however, I was unable to. 
Since Jellyfish are iconic creatures of the sea, they should be represented as a unicode point. Many people identify and relate with Jellyfish and are should be able to express this symbolic relationship through an emoji.

Another very practical reason for having a Jellyfish emoji, is to let people know when you have been stung by a dangerous Jellyfish and require medical attention. Jellyfish emojis will save lives.

Also, Jellyfish are cool.