A Collage of Nudibranch Colors
Nudibranchs are a kind of sea slug, and their 3000 species are found from the poles to the tropics in both shallow and deep water. Though they often only reach two centimeters in length, they are famous for their spectacular color patterns. Nudibranchs get their name from greek (nudi) and latin (branch) words meaning "naked gills". There are two main types of nudibranchs: dorid nudibranchs look fairly smooth, with a tuft of feather-like gills toward the back of the animal that are used to breathe. Aeolid nudibranchs instead breathe with organs called cerata covering their backs.
Unlike most snails, nudibranchs lack a shell that can be used for protection from predators (they shed their shells as larvae). This means that nudibranchs must defend themselves in other ways. Some nudibranchs use camouflage to blend in with their environments, while others use very bright and contrasting colors to signal to predators "watch out." Many aeolid nudibranchs have evolved the ability to ingest and reuse stinging cells from their prey.
A Baltic Sea Nudibranch
Nudibranchs are mollusks that have evolved from shelled ancestors. They're often noted for their vibrant colors and striking forms (like the reddish-orange Coryphella verrucosa shown here) that help to dissuade predators from taking a bite, important since they lack the protection of a shell.
© OCEANA Carlos Minguell
The feathery strands at the back of this dorid nudibranch (Chromodoris willani) are no mere adornment: they’re its gills! There is also a pair of antennae up front. This species, found in Western Pacific Ocean coral reefs, ranges from dark purple to bright white.
The Spanish Dancer
The Spanish dancer (Hexabranchus sanguineus) is one of the largest species and best swimmers of the nudibranchs. When the Spanish dancer swims, the wide edges of its mantle (the parapodia) are pushed through the water in a graceful undulating movement reminiscent of flamenco dancers. The Spanish dancer is also known for covering its egg cluster with toxins taken from its venomous food in order to protect the eggs from predators.
Tony Brown, Flickr
The Comeback Sea Slug
This nudibranch (Felimare californiensis) is making a comeback to a location it hasn't been to in years. First discovered off the coast of Southern California in 1902, it was thought to be extinct in the region since 1984 due to pollution. But the nudibranch, with its blue and gold color scheme (matching the University of California), has been spotted off the Southern California coast several times since 2003. Scientists have their fingers crossed that this indicates a larger comeback for the species.
Nudibranch With a Shrimp Partner
Amidst the bright blue tufts and the dark blue fringes of the beautiful Risbecia tryoni, you might not even notice the red emperor shrimp (Periclimenes imperator). The two animals are native to the Indo-Pacific region and are often found accompanying each other. The nudibranch eats sponges, while its shrimp partner feeds on worms. Both are small creatures, with the nudibranch typically reaching 60 millimeters in length.
Douglas Good, Pennsylvania
This beautiful turquoise and purple creature is an aeolid nudibranch. The aeolid nudibranch is covered by branches that are actually gills, called cerata. The cerata also contain parts of the nudibranch’s digestive system.