# What is this??



## solarz (Aug 31, 2010)

Just saw this today. Can anyone tell me what it might be? Thanks!


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## 50seven (Feb 14, 2010)

Some kind of sea cucumber?

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## solarz (Aug 31, 2010)

aren't sea cucumbers more rounded? This critter looks more flat-ish.


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## carmenh (Dec 20, 2009)

Does he have a hard shell?


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## solarz (Aug 31, 2010)

carmenh said:


> Does he have a hard shell?


I have no clue, I didn't poke it or anything... 

But, judging from the look of it, I'd say no. It's got these little feather-duster-like things sticking out on its back.


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## Will (Jul 24, 2008)

It's a nudibranch.


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## solarz (Aug 31, 2010)

Will Hayward said:


> It's a nudibranch.


Is it good news or bad news? Since it apparently grew up in my tank, and I don't have any corals, I guess I don't have to worry about its diet? Is there anything I should watch out for? I think it spends most of its time under the sand.


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## Will (Jul 24, 2008)

solarz said:


> Is it good news or bad news? Since it apparently grew up in my tank, and I don't have any corals, I guess I don't have to worry about its diet? Is there anything I should watch out for? I think it spends most of its time under the sand.


It's hard to say. It's not a bad sign that life is surviving in your tank, but not all life is truely desireable.

I've seen this or a very similar variety before, and witnessed it consuming various types of algae and such growing on live rock. It's so perfectly camoflauged it could probably stay hidden on the rock in plain sight and be overlooked by yourself many times. Now that you've seen it, you'll be spotting it more often.

There are some 3000ish species of nudibranch, so identifying certain species can be quite difficult, others due to their gawdy colours or "coral mimicking" apendages can be recognised easier. In addition, they come from all around the world in many marine habitats. The need to identify them is important because many or most species have very specific feeding habits and dietary requirements. It is widely recomended that you never buy a nudibranch without 100% positively identifying the exact species, learning it's habits and main food source, and being able to supply it. Some nudibranchs main diets are even other nudibranchs. More fascinating is the various evolutions certains ones have adapted, some mimic the coral they eat, some learned to swim, some wear colours to show they are toxic, etc.

Fortunately this one has appeared in your tank, and so has probably had a food source in the tank. If you can't ID the species, there's not much you can do other than closely observe it's habits. What does it search for? What does it eat? How does it react to X? write some notes and you'll create your own basic care guide. If you don't observe it eating after a while, try offering nori, algae wafers, frozen gel spirulina. If it doesn't take any interest whatsoever in those, it might not be a plant eater and has been eating something else that lives in your tank.

Like many inverts, they are very sensitive to salinity change. They often get chewed up by pump impellers, maybe going in to eat the gunk off the plastic.


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## solarz (Aug 31, 2010)

Will Hayward said:


> Like many inverts, they are very sensitive to salinity change. They often get chewed up by pump impellers, maybe going in to eat the gunk off the plastic.


Thanks Will! I hope it doesn't actually manage to crawl into the propeller...


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## Will (Jul 24, 2008)

solarz said:


> Thanks Will! I hope it doesn't actually manage to crawl into the propeller...


To be safe, just flip it off and place it on rock. Wash your hands afterwards.


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## sig (Dec 13, 2010)

it could be Polynoidae 
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