For electric damage, lets stick with 1d4 as the original but not allow a save due to the conductivity of salt water. Also, do we want to retain the double damage to characters wearing metal armor?
The skills...maybe put a rank or two into Hide, actually. Cephalaspis would be raking around in the mucky bottom waters, and it wouldn't be too far a stretch to say possibly actually partially burying themselves in said muck.