Brittlestar (Ophiothrix sp., red) on a collapsed sea pen (Pteroeides sp., orange) in which a few porcelain crabs are hiding and a small fish is resting. Sea pens are a type of octocoral. The brittle star is a marine invertebrate that is related to starfish. It has five flexible arms radiating from a central disc-shaped body, which means that unlike starfish it can use its arms to walk on the sea floor. Its mouth is underneath its body. Some brittle stars scavenge on debris on the sea floor, while others use their arms to filter food from the water. Photographed off Rinca, Indonesia.