No they are vertebrates and chordates.
Yes they do.
They don't.
they are not endangred
All eels are vertebrates due to the fact they all have backbones, this is what defines a vertebrate.
Santa Rides an Eel
Scandinavian Silver Eel Farming
DL's No-Foul Rabbit Eel Fishing Fly Part 2/2
DL's No-Foul Rabbit Eel Fishing Fly Part 1/2