Brittle star (Ophiothrix sp.) on a sponge. This marine invertebrate is found in depths below 500 metres and is related to the 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. It feeds by scavenging for debris on the sea floor, but it will also use its arms to filter food from the water. Photographed in Lembeh Strait, North Sulawesi, Indonesia.