Yellow Ornate Ghost Pipefish pair (speaking of crinoids) living in a yellow crinoid/ As is true of many sea creatures, the large one is the female (4 inches long), and the small one is the male (2 inches).
You'll note two recurring themes in this gallery: Camouflage (critters like these that blend in so predators can't see them), and Bright/Warning shapes and colors (to make predators think twice). [Taken at Anilao, Philippines]