My coloring book’s drawing of one of my favorite fish vs. a real photo, in case you wondered how much I stylized it (very little), and a nice scientific diagram of how its mouth works!

It basically has very large jaws and a large, expandable mouth cavity, but a foldable membrane seals all but a tiny opening between those jaws, and I genuinely don’t know whether you should describe that as an animal with a small mouth or a large mouth. I guess we think of “mouth size” as the opening? But most things with a smaller mouth have smaller jaws to match it.

I quoted one of its earliest known descriptions that compared the jaw structure to bellows:

Which is a perfect description of the physical structure, but this isn’t a very common item anymore, so if you still don’t get what this means, this animal’s mouth works on the same principle as pulling back on a syringe:

Opening the jaws and expanding the mouth cavity forces water inward through that tiny hole at extreme pressure. Its deep, tubular eyes are capable of depth perception far more accurate than our own, and it even achieves color vision in near total darkness! The thin but strong suction current ends up like a laser-focused tractor beam against tiny enough prey.