nerites and something else?

Got a picture of the little horned nerite in the tenner, here's a view of his underside you can see the little protrusions on his shell.

I think of him as my bumblebee snail.

He's much smaller than Mavis the tomato nerite. (And there's an oto upside-down cleaning a leaf!)

It turns out the horned nerite in the big tank is female, she's laying eggs everywhere now too.

A day after introducing the new fish/snail to Oliver's tank I saw all these little white specks jumping and darting around. Too small to picture- even smaller than the small specks in this picture (the three white dots under Mavis are the eggs, that gives an idea how tiny) did a bit of research I guess they are copepods harmless things. But that clear-looking stem thing below Mavis- is that a hydra in my tank?? (the white horizontal line is rubber band holding the anubias plant down)