Hitch hiker ID help please

[HiImKevin1]

Hi everybody, I started a 20g reef about a month and a half ago, and I've found about 6 of these little hitch hikers in my tank, I took the photos with my iphone so the quality isnt that great, but from what I can tell it is mostly black with black bands on the arms along with transparent/light green bands. The largest one ive found is about an inch and a half diameter. I wanted to know if these were okay to leave in the tank or should I be picking them out as i can catch them? Any help is much appreciated. thanks

 

[impur]

Brittle star :) These are good guys and will eat left over food and detritus. They hide in the rocks, and when you feed you will see a million little legs sticking out trying to grab food.

 

[HiImKevin1]

sounds good. thanks