Electric Scallop

if those die dont they poison your tank

Nope, they are non-poisonous.

are they easy to keep and what kind of lighting do they need?

I had wanted one of those, but I heard they are hard to keep and don't live very long...

Their lighting requirement is low. Spot feeding is required at least a few times a week and they live from 2-5 years if taken care of, also depends on their age when acquired.

i bought one and it flapped into the back of my rock structure as soon as i dropped it in and never saw it again lol.

yeah they don't live very long, i had one too, actually i don't remember what happened to it.