Contributed by TPERP Ginny Buerger

Opalescent Nudibranch
D. Wieder

Opalescent Nudibranch
(Hermissenda crassicornis) 

Rosy Nudibranch
D. Wieder

Hopkin’s Rosy Nudibranch
(Okenia rosacaea)

Where to find them: They are found throughout the world’s oceans, but are most abundant in shallow, tropical waters. The two species above are common at Cabrillo.

 What do they eat: They are carnivores that slowly graze on algae, sponges, anemones, corals, barnacles, and even other nudibranchs.

“Nudibranchs eat using a radula, which is many rows of tiny teeth, used to scrape food off rocks. They are carnivorous – their prey include anemones,sponges, coral, hydroids, barnacles, fish eggs, sea slugs, and other nudibranchs. Nudibranchs are picky eaters – individual species or families of nudibranchs may eat only one kind of prey. Nudibranchs get their bright colors from the food they eat. These colors may be used for camouflage or to warn predators of the poison that lies within.

To identify prey, they have two highly sensitive tentacles, called rhinophores, located on top of their heads. Nudibranchs derive their coloring from the food they eat, which helps in camouflage, and some even retain the foul-tasting poisons of their prey and secrete them as a defense against predators.”  

Who eats them: They are prey for fish in the tidepools. See the adaptation below to withdraw their tentacles to reduce the likelihood of being spotted by predators.

Adaptations: “The bottom-dwelling, jelly-bodied nudibranch might seem an unlikely canvas for Mother Nature to express her wildest indulgences of color and form. But these shell-less molluscs, part of the sea slug family, bear some of the most fascinating shapes, sumptuous hues, and intricate patterns of any animal on Earth. “New” varieties of nudibranchs are being discovered constantly.

“Nudibranchs also may have tentacles on their heads that help them smell, taste and get around. A pair of tentacles called rhinophores on the nudibranch’s head have scent receptors that allow the nudibranch to smell its food or other nudibranchs. Since the rhinophores stick out and can be a target for hungry fish, most nudibranchs have the ability to withdraw the rhinophores and hide them in a pocket in their skin if the nudibranch senses danger.”

Reproduction: “Nudibranchs are simultaneous hermaphrodites, and can mate with any other mature member of their species, which means they have reproductive organs of both sexes. Since they can’t move too far, too fast, and are solitary in nature, it’s important for them to be able to reproduce if the situation presents itself. Having both sexes means that they can mate with any adult that happens to pass by. They lay masses of spiral-shaped or coiled eggs. The eggs hatch into free-swimming larvae which eventually settle onto the ocean bottom as adults. Their lifespan varies widely, with some living less than a month, and others living up to one year.” (

What’s their life like: Nudibranchs live about one month to one year. They are carnivores, moving about on their gastropod’s foot to seek food such as coral, algae, anemones and barnacles. They range in size from less than an inch to about 12 inches and may weigh up to 3 pounds. Most are about the size of a teacup or smaller.

Nudibranchs have a shell in their larval stage, but it disappears in the adult form. Gastropods also have a foot (more on that below) and all young gastropods undergo a process called torsion in their larval stage. In this process, it’s like they are doing a hand stand, with their feet still on the ground, but their butts are twisted 180 degrees and over their heads. Torsion is a difficult concept to explain. Thus they spend their lives standing on their heads, so to speak.

 Interesting facts: Some nudibranchs are solar-powered, storing algae in their outer tissues and living off the sugars produced by the algae’s photosynthesis.

 Their scientific name, Nudibranchia, means naked gills, and describes the feathery gills and horns that most wear on their backs.

Phylum: Mollusca
Class: Gastropoda
Family: sea slugs
Scientific Name:   nudibranchia
Common Name(s): nudibranchs or sea slugs

Source(s) of Information:

Some other types of Nudibranch and Dorids

California Aglaja – J&W Tam
McDonald’s Dorid – J&W Tam
Hopkins Rose Nudibranch – J&W Tam
Hopkins Rose Nudibranch – G. Kidder
Opalescent Nudibranch – J&W Tam
Porter’s Chromodorid – J&W Tam
Rabbit Dorid – J&W Tam
San Diego Dorid – J&W Tam
Violet Fan Nudibranch(Spanish Shawl) – J&W Tam
Violet Fan Nudibranch(Spanish Shawl)- J&W Tam
Yellow Umbrella Slug – J&W Tam

Last revised 23-Jan-20