Fish are streamlined for propulsion.
Their bodies create little friction between them and the water that supports them. Light filters down from the water’s surface where we aquarium visitors watch the fish take graceful turns around the tank’s curves.
In another tank, jelly fish, have tentacles lit by back light.
They are transparent, catching food in their tentacles and letting themselves be propelled by currents or by ingesting water and spitting it out to move in any direction.
They are other worldly.
Living without a backbone takes friction out of your life.