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CanadianReefer · May 27, 2018

Poking around my aquarium at night, I found a few odd creatures. Can anyone provide insight? The one I think may be an asterina starfish, but I understand they are small. I have one that is at least the size of a toonie (it's a Canadian thing) and is frequently found wrapped around one of my sps corals, as shown in the first photo. I wonder if that's why that coral has been struggling lately??

The crab - not sure if he's good or evil - but he's pretty big for a crab.... looks red with orange eyes and a mix of orange and black coloured dots.

Lastly, this algae is something I've never had before. It looks glossy like bubble algae but it is tiny little stick-like patches.

Sashaka · May 27, 2018

The first picture may be a flatworm or a nudibranch: The second pic is a type of asternia starfish: There are many types of green algae. Most are not sutible for the main display as they like to take over the tank: http://www.saltcorner.com/LMAM/ShowChapter.php?ChapterID=18 and http://homeaquaria.com/saltwater-algae-control-the-ultimate-guide/
The creature in the hole in the rock, wow! I have no idea. If you can get it out for a better look, please show us! It almost looks like an octopus or squid of some type based on what we can see, but it could be something entirely different once you can see the whole thing. Maybe someone else here can id it. I'd love to know too!

cloak · May 27, 2018

I can't really make anything out in the first picture, but that might be an Asterina star in the middle of the photo and a little to the right. (attached to the coral) If so, eating sps corals is definitely not unheard of. As far as that crab goes I don't know what kind it is exactly, but I sure wouldn't want it in my tank. They're just too unpredictable. The algae might be some type of Cladophora. (herpestrica?)