Original: The bathypelagic, abyssopelagic, and hadopelagic zones are very similar in character, and some marine biologists combine them into a single zone or consider the latter two to be the same.
Simplified: The bathypelagic, abyssopelagic, and hadopelagic zones are very similar in character, and some marine biologists count them as a single zone or consider the latter two to be the one zone.