Barnacle Eating Dorid

by Hailey Surgin

Common Name:  Barnacle Eating Dorid
Scientific Name: Onchidoris bilamellata
Size Range: 6  mm(0.25 in) up to 30 cm(12 in)

Identifying Features:
Most Barnacle Eating Dorids have a mottled grey and brown colour to them. Their mantle, which is an outer layer of tissue that contains the viscera and secretes the substance that puts together the shell in other molluscs, has a brown and white pattern on it. Young dorids, and some mature adults may be completely white.  Towards the head are white club shaped tentacles called rhinophores.  They also have a circular gill plume near their posterior.

Throughout all the regions that Barnacle Eating Dorids live, they are all very similar. They are all sublittoral, which refers to a region that is near the shore where animals inhabit and grow as well as the area from the shore that reaches out to one hundred meters.  The depth of these areas can be up to twenty meters below sea level.

The Barnacle Eating Dorid, as mentioned in it’s name, really only eats one thing. Barnacles. The way that they eat the barnacles is by drilling into it with a specialized radula. Other parts of it’s diet also includes sponges, anemones, and coral.

There is little information about specific predators of this species.  However, when they are disrupted or disturbed, they secrete acids that act as deterrents.

Life Cycle:
Not a great deal of information is known about this specific nudibranch, but most nudibranchs are simultaneous hermaphrodites.  A simultaneous hermaphrodite is an organism that can mate with any other mature male or female of their species as they have both male and female reproductive organs.  When Onchidoris bilamellata reproduces, they come together in large groups to mate and lay eggs in shallow water.  The life span of a nudibranch varies widely. Some live for a month, whilst others can live for almost a year.


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Opalescent Nudibranch         

by Allie and Charlotte

Common name :  Opalescent Nudibranch

Scientific name :  Hermissenda crassicornis

Size range :  up to 3″ inches long.

Identifying Features   

The Opalescent Nudibranch has a mid-line orange patch on its translucent back. It is slender and small in stature and is without shell or operculum. It also lacks a mantle cavity and is covered in many cerata topped with orange and white tips. Sometimes, the patch of vibrant colour on its back can be deep blue. The Opalescent Nudibranch has a yellow green body with a peacock-blue line around its sides. The pearly white tips of the cerata contain many defensive nematocysts.  The head has a pair of rhinophores (tentacles) and it lacks a gill plume near its back end.


The Opalescent Nudibranch lives on eelgrass beds, rocks, mud flats, docks, and certain other rocky intertidal areas from Alaska to as far as Baja California or even Kodiak Island and Japan. It is found from the intertidal zone to 115′ deep but it can live at virtually any depth of sea water. They thrive in shallow, warmer water and are larger and more common in these areas.

Food (Prey)

Nudibranchs feed on hydroids, sponges, sea slug eggs or sea slugs, sea squirts, pieces of fish, other mollusks and sometimes anemones and barnacles. All are carnivorous and feed on a wide variety of animals. The Opalescent Nudibranch is one of the few cannibalistic species of nudibranchs.


There are few if any documented predators of the Opalescent Nudibranch except for other cannibalistic Opalescent Nudibranchs.  Many nudibranchs have evolved to blend in with surrounding plants in order to avoid all predators while others have evolved to be brightly coloured to warn predators that they are or may be poisonous. They can also use an assortment of chemical defenses that make them toxic to predators that may include releasing a mucus-like acid from their skin when they come in contact with a potential predator.  The Opalescent Nudibranch is brightly coloured to warn off predators because the tips of its cerata are armed with unexploded nematocysts from hydroids it has eaten.

Life Cycle

Nudibranchs are hermaphroditic but are unable to fertilize themselves. They also tend to lay their eggs in a gelatinous spiral. The Opalescent Nudibranch is common, abundant, and has a life cycle of four months. Other species of nudibranches can live up to a year, and a 6 year life span has been reported when the nudibranch is inside an aquarium.

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