To determine which zone is located on the ocean floor, we need to examine the definitions of each zone listed in the options:
1. Benthic Zone: The benthic zone refers to the ecological region at the lowest level of a body of water. This zone includes the sediment surface and some sub-surface layers. It is where organisms such as crabs, lobsters, and bottom-dwelling fish reside. It encompasses the ocean floor.
2. Neritic Zone: The neritic zone is the shallow part of the ocean above the drop-off of the continental shelf, approximately 200 meters (660 feet) in depth. While it is a vital marine zone, it is not located on the ocean floor itself but rather the water column above it.
3. Pelagic Zone: The pelagic zone refers to the open ocean, including the water column from the surface to the ocean floor but not the ocean floor itself. This zone is divided into various sub-zones based on depth but does not include the seafloor.
Given these definitions:
- The benthic zone is the one located on the ocean floor.
Therefore, the correct answer is:
A: benthic
