Nudibranchs: the Most Colorful Animal Under the Sea

Nudibranchs are very small so they are not that easy to find when you're out snorkeling or scuba diving. However, they are extremely colorful so keep your eyes open for an unusual color, and don't forget to get close to walls and wrecks to see if you can find them. There are more than 3000 species, ranging from 20-600 mm. How many names can you remember?! The name "Nudibranch" means "Naked-Gill."

Although Nudibranchs and Sea Slugs are often confused with each other, they are actually members of a different taxonomic group.

Nudibranchs are carnivorous, feeding on sponges, hydroids, sea slugs or their eggs. Occasionally, they will eat other Nudibranchs. The surface dwelling nudibranchs eat jelly-fish type creatures.

There are 2 main ways in which nudibranchs defend themselves. The first is by blending into their surroundings so they are not easily noticed. The second is by having extremely bright coloration, which serves as a warning to predators that they are distasteful in some way.

Some of the less common defense methods include:

Some Nudibranchs eat jellyfish, or other stinging animals and are able to pass the stingers through their digestive system without harming themselves. Then, they place the stingers upon their skin to protect themselves.

The final mode of protection is chemical. Some Nudibranchs produce their own acid, or chemical defense, while others use the food they ingest to aid in this production.

Nudibranchs are common around the world, living in all the world's oceans, at virtually all depth levels. However, they are bigger and more varied in shallow, warm waters. It's very unusual to see them in mid-water because they prefer to be attached to something, either a rock, piece of kelp, a shipwreck or coral.

Nudibranchs are hermaphoridites, that is they possess both male and female organs. When nudibranchs meet for mating, both partners give and donate sperm. This helps the species reproduce because any mature individual can mate with any other one. The couple face together, but in opposite directions with their right hand sides touching. After fertilization, nudibranchs deposit their eggs in a gelatinous spiral. It's thought that self fertilization is possible, but it's uncommon.