By Ken Schwab
Nudibranchs are arguably the most strikingly beautiful creatures in the oceans. The name is derived from the Latin word nudus for naked and the Greek word brankhia for gills and pronounced ‘noo-duh-brangk.’ They are distinguished by their fascinating shapes, elegant colors, and intricate patterns.
Who are these critters?
These vibrantly colorful critters are found throughout the world’s oceans and are most abundant in shallow and warm waters. New species are being discovered almost on a daily basis and currently there are over 3,000 known species. The typical lifespan fluctuates from just one month to one year. They are bilateral in symmetry, oblong in shape, and vary widely in girth and length. When nudibranchs mature, their size ranges from a quarter of an inch to 24 inches long, and they can weigh up to 3.3 pounds!
Nudibranchs start life as a shelled larva but, unlike snails, they eventually shed their shell as an adult. It is this feature that will aid in the understanding of the mollusk’s evolution. Most species of snail have developed a shell for protection. The nudibranch, however, is an exception.
One fascinating characteristic of the nudibranch is that they attain their color from the food they consume. Nudibranchs are carnivorous and their diet consists of, but is not limited to: algae, sponges, anemones, corals, barnacles, and even other nudibranchs. They utilize highly sensitive tentacles on top of their heads, which are called rhinophores, to find their prey.
Inside and out, these creatures are fascinating for many reasons. For one, nudibranchs have an ability to retain poisons from their prey and then secrete these toxins (nematocysts) as a defense mechanism against other predators, hence no armored shell is needed. Second, they conform to the ‘green’ movement, and are in essence solar-powered. The algae they consume accumulate in their outer tissues, where they goes through photosynthesis. As a result, the algae generate sugar, which the nudibranch uses as another source of energy. Incredible!
Nudibranchs are simultaneous hermaphrodites, meaning that they posses both male and female sexual organs at the same time. However self-fertilization usually does not occur, they must mate with another member of their species to reproduce successfully. They lay their eggs in a mucous mass onto a hard substrate such as a rock.
Why are they important?
Nudibranchs are an indicator species. A decrease in their abundance or variety serves a warning sign that the ecological system in which they reside is degrading. They also have made significant contributions to the medical field. By studying their large and individual nerve cells (neurons), scientists are gaining a better understanding of the nervous system of humans. In addition, the organic compounds that are produced by the nudibranch can be used as medicine to deter the growth of cancerous cells.
Where can you see them?
A sure-fire method is to visit a local aquarium. A more real-world experience would be to throw on your best scuba gear and hop into the ocean. These colorful creatures can also be found in local tide pools and bays like Tomales.
Image credits (from top): David Doubilet, Ammer Steven Naber, Erwin Kodiat
