The marine creature is a young Bearded Fireworm, about 2 in length. The worms can grow to be 4-6. The white bristles surrounding the worm can cause a painful burning sensation and irritating wound. The background is a colony of coral polyps.
The photo was taken while diving in Bonaire. The equipment used was a Nikonos V underwater camera, 35mm lens with extension tubes for 1:2 macro, and a Nikonos 105 strobe.