It extends from 4000m to the sea floor. The only zone deeper than this is the hadal zone, which includes areas found in deep sea trenches and canyons. This zone is home to pretty inhospitable living conditions, which include near- freezing temperatures and crushing pressures. This deep water squid is just one of the several squids and octopus that live in this zone. Note how this one is completely transparent, and has photophores on it's tentacles to attract food and warn away predators.
Basket stars are just one kind of echinoderm that flourish on the sea floor.
Basket stars sit on the bottom, or attached to tall sessile animals, with their flexible arms raise above them to catch floating and falling organic particles. Their arms are quite fragile, but can regenerate quickly. This specimen has an armspan of over 25cm. The seapig is a rather grotesque looking relative of the sea cucumber, another echinoderm. These are one of the most common macroscopic animals pulled up in bottom dredges.