The Frosted Nudibranch

by Elias and Jesse

Common name:  Frosted Nudibranch

Scientific name: Dirona albolineata

Size range: up to 180mm (18cm) in length

Identifying Features

Frosted Nudibranchs are soft bodied organisms similar to slugs. In the general, nudibranchs are often referred to as sea slugs. Frosted Nudibranchs can range anywhere from 20- 600mm long, but their most outstanding, and identifiable feature, is the frosty white tips on the cerata on their back. They come in a wide variety of colours, including mauve and peach, and for the most part, they’re translucent. The Frosted Nudibranch is known to shed its cerata when stressed.


The Frosted Nudibranch thrives along the shores of Japan, Siberia, and Southern Alaska, to Southern California. It is found intertidally and up to 37m deep.


Most sea slugs have very specific feeding needs, thus making them difficult to keep in aquariums. The Frosted Nudibranch has powerful jaws enabling it to crack open snail shells. This nudibranch has a vast selection of prey including arboresent and foliose bryozoans, hydroids, small prosobranchs, crustaceans, and ascidians.

Life Cycle

Nudibranchs are hermaphrodites. They have both male and female reproductive organs. In most cases, two separate organisms will exchange sperm. But there is a potential for self fertilization. Once the eggs are fertilized, they are laid in large amounts, often very close to a food source. Once hatched, they are in the trocophore larvae stage, characterized by a round shape, and numerous sensory and defensive hairs. The veliger larva stage is the stage in which young nudibranchs hatch. Eventually they abandon the water column, and travel to the bottom, becoming benthic. It is at this point, where they undergo metamorphosis, and become juveniles.

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Blue Top Snail

Author: Alisha Carey

Common name: Blue Top Snail

Scientific name: Calliostoma ligatum

Size range: up to 2.5 cm (1 inch) in diameter

Identifying Features:   The Blue Top Snai (Calliostoma ligatum) is part of the Callistomatidae family. It has a brown shell with tan to orange spirals. Its inner layer its pearly blue, and the foot of the snail is orange. When the outer layer of the shell is worn away the top of the shell (or the whole shell) may also look blue which is why it is called a Blue Top snail.

Habitat: Blue Top Snails are found in tide pools or up to 30 meters deep in the ocean. They can be found from Alaska to California. Blue top snails keep to rocky areas and kelp beds.

Food: C. ligatum eat a variety of algae and kelp. It eats by using its radula teeth (a ribbon with rasping teeth.)

Predators: The Blue Top snail protects itself by hiding within its shell. Some of their predators include shore birds, fish, crabs and other snails.

Life Cycle: In general, snails are considered sexually mature by the time they are one year old. The C. ligatum has both female and male organs. It produces eggs which it fertilizes inside. Then they release the eggs and they are attached to rocks and seaweed but some eggs can be found in the sand.

Photos by D. Young

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Black Katy Chiton, Black Leather Chiton

Author: Sarayut Uddy Klongchoengrob

Scientific name: Katharina tunicata

Size: to 15cm in length

Identifying Features

The Black Katy Chiton is oval shaped and has 8 white over-lapping plates on top of its leathery black mantle. It can grow to around 15cm in length. It has a large muscular foot to help it move and in the mantle cavity around its bottom edge they have around 50-60 rows of gills called ctenidia that they use for respiration. Underneath the chiton you will see the head and mouth in front of the foot. It does not have any eyes or tentacles, but its shell has light-sensitive organs.


Black Katy Chitons are commonly found in the San Jaun Islands and Straight of Jaun de Fuca. They are found intertidally and occur up to around 40 meters in depth.  They are mostly found attached to rocks and they are unique compared to other chitons because they tolerate direct sun light.


Black Katy Chitons like other chitons, feed by slowly grazing on brown and red algae using a long rasping structure known as a radula. It is also known to have eaten small sponges and tiny barnacles.


Black Katy Chitons have only a hand full of predators such as sea urchins, the Leather Star (Dermasterias imbricata), and Oystercatchers (Haematopus bachmani). They avoid being eaten by blending in to their surrounding by being a really dark color with contrasting white plates which breaks up their shape.  Algae sometimes may grow on top of them allowing them to blend in more with their surroundings. They also have a hard mantle and can be tightly attached to rock making them very hard to remove.

Life Cycle

The Black Katy Chiton reproduces out the body where the male releases sperm into the ocean or in the mantle cavity of the female where the sperm would meet the egg. When the egg is ready it hatches into a free swimming trochophore larva. The larva then elongates and the shell gland secretes the plates of the shell. There is no intermediate stage.

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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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