Jellyfish are creatures found in Splatoon and confirmed to return in Splatoon 2. They can be found walking around Inkopolis, wearing various articles of clothing. The series' jellyfish highly resemble real-life jellyfish. However, the jellyfish in this game are highly anthropomorphized to the point of having eyes and being bipedal, likely from similar evolutions to those of the Inklings and Octarians.
Jelonzo is a blue jellyfish who owns Jelly Fresh, a clothing store in Inkopolis. Most jellyfish in Inkopolis cannot speak the Inkling language; while Jelonzo is an exception, he is only able to speak Inkling with a thick accent, which the English localizations, translate as Engrish.
Marie of the Squid Sisters references this species in advice for Arowana Mall: "Float like a jellyfish, sting like a… jellyfish?" Because the stores and restaurants in the mall are themselves filled with jellyfish, this mention may have been an intentional joke, not a coincidence.