A colorful crab and sea urchins make for a psychedelic scene in Clallam Bay, Washington. Marine invertebrates, sea urchins use their spines to move along the seafloor, and crabs are known to be their natural predators.
Komodo National Park in Indonesia showcases a carnival of marine life, including this green-and-black nudibranch, seen here devouring a tunicate. The coloring of these carnivorous mollusks comes from the foods they eat.
As if translucent spaceships in a night sky, hooded nudibranchs pulse in the waters of God's Pocket Marine Provincial Park in British Columbia, Canada. These sea slugs flex their bodies to swim and can reach lengths of half a foot (15 centimeters) .
A smooth trunkfish (Lactophrys triqueter) swims through its coral habitat off Grand Turk Island in the Caribbean. Solitary in nature, the trunkfish blows water out of its mouth to expose prey such as mollusks, crustaceans, worms, and sponges.
A Denise's pygmy seahorse (Hippocampus denise) takes its place among coral polyps in Indonesian waters. At less than an inch (2.5 centimeters) tall, the seahorse's size and coloration help camouflage it within the gorgonian coral.
A goby fish (Trimma okinawae) peers out of a sea anemone in the Solomon Islands. Gobies are serial sex-changers: They can go through both male and female phases.
A flamingo tongue sea snail (Cyphoma gibbosum) feeds from the top of a sea fan in the waters off Grand Turk Island. These predatory mollusks leave a noticeable trail of dead coral tissue in their wake.
The waters of Bali, Indonesia, are home to this otherworldly creature, a peacock mantis shrimp (Odontodactylus scyllarus). The shrimp feeds by smashing open its prey until it can feed on its tissue.
Look closely at this tapestry and you'll find an emperor shrimp and a crab on a sea cucumber. In this symbiotic relationship, seen here on Fiji's Rainbow Reef, the sea cucumber offers camouflaged protection (and possibly a ride) but is not harmed by its neighbors.