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Brittle star id


Blue Ring
Oct 19, 2008
can anyone tell me what species of brittle star this is and it if would be compatible with an O. Cyanea? initially i thought it would be fine until i read about green brittle stars being highly aggressive and bad tankmates. it was found in queensland australia and hitched a ride into my tank with my live rock (along with several others). its arms are roughly 8 inches long and when my octopus arrives i am expecting it to be between 2 and 4 inches.

one of the reasons i think it might be ok, even if it is somewhat aggressive and tries to steal food from the octopus is it heads for cover as soon as i turn the lights on and the cyanea is diurnal, so they shouldnt cross paths, unless it tries to eat the octopus in its sleep or something.

also, does anyone know what that weird round thing is underneath it?

my tank is still cycling so if the water quality etc looks horrible thats probably because it it. i finally turned my skimmer on today and im shocked at how quickly and how dramatically its made a difference.


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Oct 4, 2008
Sorry I cant give you a name for the sea star other than "brittle sea star", but they are very common and dont seem to worry the fish or corals in my tank. Having said that I don't have any as big as the one you mentioned. If you do a google search under images, they show quite a few and list then as "semi-aggresive".

As for the weird "round thing" same story ....no name, but I see something very similar growing on the underside of rocks in rock pools. They feel like some sort of "sponge", if it doesnt die off during the tank cycle it should be ok. haggs


Colossal Squid
Nov 19, 2002
the weird round thing is a golfball sponge perhaps Tethya sp

Your star looks a bit like Ophiothrix sp which I think are fairly common in Queensland