Macro

Spanish Dancer

Hexabranchus sanguineus · Marine gastropod mollusk — family Hexabranchidae; one of the largest nudibranchs known

Most nudibranchs crawl; the Spanish dancer, disturbed, lets go of the reef and swims — mantle skirts flaring and rolling in the deep-red flamenco motion that named it. It ranks among the largest of all nudibranchs, a crimson animal that can reach forearm length, and it is almost strictly nocturnal, which makes it a signature night-dive find across the Indo-Pacific and Red Sea. By torchlight look for one plowing across open reef between sponge meals, often carrying passengers: emperor shrimp ride the mantle folds like deckhands. Its eggs are as recognizable as the animal, a rose-shaped ribbon of pink spirals fixed to hard bottom and chemically defended like the adult. Watch a voluntary swim from a respectful distance; forced performances exhaust an animal with nowhere to hide.