Strange and Beautiful: Nudibranchs!

Wednesday, April 24, 2013 by Caroline Casals

What on Earth are these strange, colorful creatures?  You my friend, are looking at the spectacular and reclusive nudibranchs!   Nudibranchs (new-dee-brank-s) are animals that live all over the worlds oceans, and are related to our own land-lubber slugs and snails.  That relation gives them their common name 'sea slugs'.  Such a lowly name however, is hardly fitting of some of the most spectacular and varied animals in the world! 


Nudibranchs come in almost every shape and color imaginable, and can live at great depth or in the shallowest of tide pools.  All snails, slugs and sea slugs move with one big muscular foot, but some of these aquatic beauties have another trick up their sleeve that would make every one of their land locked brethren weep with envy: they can swim! By flapping flattened "wings" on their sides, the nudibranchs can glide through the water.  You can watch a video of it here

The beautiful colors of these animals carry a deadly serious warning: I AM POSIONOUS! 


Even though some nudibranchs can swim, they are slow and small compared to most of the fish and other animals they live with.  Their best defense is to have stingers, be disgusting tasting or even toxic, and to let everybody know it!  This color strategy that is used by poisonous animals all over the world is called aposmatic coloring.  This color strategy even works with us humans – I bet you leave that bright yellow and black wasp very much alone!  Not all animals that are bright colors are poisonous, toxic or sting, but most of us don't take the chance and leave them be. 

Be afraid mantis shrimp... be very afraid!

Even though many of the most colorful nudibranchs live on coral reefs in tropical seas, there are more than 45 species that live here in the Gulf of Maine, such as the cryptic Dendronotus frondosus aka. 'bushy-backed nudibranch' and the 'shag-rug nudibranch', Aeolidia papillosa.


 Dendronotus frondosus (left) Aeolidia papillosa (right)

Although you might be tempted after seeing these beautiful animals to bring one home to your aquarium, be warned, nudibranchs do not make good pets and almost always starve to death.  They require very specific foods, sometimes eating only one or two species of anenome, sponge or sea squirt, and there are no artificial foods for them yet.  It is these specific food choices that might make them important to their natural ecosystems!  For now we have to leave these fantastical creatures in their wild ocean homes.


Bonus points!  Can you find the copepod in one of these pictures?

Photo credit for cover image: David Darom

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