I think we need to update the definitions of the deep benthic zones in accordance with recent advances. The GOODs biogeographic classification (2010) and Watling et al (2013) provide this analysis and I think the definitions on here are a little out of date.
According to these publications the depth zones should be as follows:
Bathyal (Upper) 300-800m Bathyal (Lower) 800-3500m (can be split into upper 800-2000m and lower 2000- 3500m portions) Abyssal 3200-6500m Hadal (or Ultra-abyssal) >6500m
References: Watling et al (2013)Progress in Oceanography 111, 91-112 UNESCO (2009) Global Open Oceans and Deep Seabed (GOODS) Biogeographic Classification. Paris, UNESCO, IOC, Technical series No. 84