Habitat: Coral reefs, usually below 10 m in depth. Distribution: Caribbean wide. Natural History Notes: Brown tube sponges are so large that small fish can live inside their hollow core. Typically smooth walled. Characteristics: Clusters or single tubes (up to 0.5 m long and 10-20 cm in diameter). Light to purplish brown externally and is yellow to tan internally. The surface is smooth, with meandering groves occasionally. Oscules on the inner walls of the tubes few mm in diameter. Through small holes in its body wall, the sponge draws in water from which it extracts food and oxygen. It pushes the water out of the large opening in its top.