Opalescent Nudibranch

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.

Habitat

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.

Predators

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.

References

Harbo, Rick M (2011). Whelks to Whales. British Columbia: Harbour publishing, Madeira Park, British Columbia

Sept, J. Duane (1999)  The Beachcombers Guide to Seashore Life in the Pacific Northwest. Harbour publishing, Madeira Park, British Columbia

(Jan 14th, 2012). Nudibranch. Wikipedia. : en.Wikipedia.org/wiki/Nudibranch

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