So far I have only one mystery here, but I'll add more later!
Dinner plates on your mouth
On muddy or sandy shores of rivers and lakes lives a small ground beetle called Dyschirius. There are many species of this genus. Some are very small (about 2 mm long), others are a bit bigger (over 6 mm long). They are odd-looking things, with a front (prothorax) that looks like a shiny ball, hinged onto a shiny, sausage-shaped back (mesothorax, methathorax, and abdomen). Most of them are black, but some are reddish brown, and others are black and yellowish. They like to eat other beetles (especially rove beetles).
Some of the oddest things about Dyschirius are their mouthparts. Females of Dyschirius have relatively normal palps (the little feelers they use while eating or while finding food), but males are odd. Their palps are swollen, with larger structures that look like dinner plates stuck onto their side. Here is a picture of the side of a palp of the female, and the side of a palp of the male:
On the left is a maxillary palp of a female Dyschirius, on the right of a male
It might be that these plates on the male are like tastebuds, allowing the beetle to taste things around it (perhaps whether a female Dyschirius it has found is of the same species!), or they might act more like suction cups. We just don't know: it's a mystery.