Soft-sediments (muds and oozes) dominate across the abyssal plain and in oceanic trenches. Organisms from most of the phyla and classes found in soft-sediments in shallow water situations occur in the deep but are represented by different genera and species. Foraminiferans, nematodes, tiny copepods, isopods, amphipods, polychaetes and bivalves are common members of the community. Larger animals include sea anemones, brittlestars, sea stars, sea cucumbers, and bottom-dwelling fishes.
Xenophyophore (Wikipedia)
The xenophyophore is a unique, one-celled foraminiferan found only in soft sediment on the deep seafloor. A huge, one-celled organism, it is covers itself in slime that traps sediments and debris. The slime hardens to form a hard protective coating called a test. Syringammina fragilissima, at a maximum 20 cm in diameter, is one of the largest protozoans known. Xenophyophores enrich the benthic habitat and areas dominated by them have been shown to have several times the number of benthic crustaceans, echinoderms, and areas dominated by xenophyophores have several times the number of benthic crustaceans, echinoderms, and mollusks than areas where they are absent.
Most animals are deposit feeders. Exceptions are suspension-feeders such as sea anemones, glass sponges, horny corals, sea pens, and stalked barnacles that have some type of apparatus for catching drifting food items. Other suspension feeders (brachiopods, tunicates, bryozoans, and some bivalves) secrete mucus to trap floating particles.
Predators are poorly known. A number of species, called croppers, are omnivores and ingest sediments, dead organic material, and live prey items. Among them are octopuses, decapods, and fishes.
