Looks like a spider

[Seaspirit]

I have a small refugium on one of my little quarantine tanks with a bit of chaeto I bought online a couple weeks ago and some biospheres. Have seen amphipods, copepods, baby bristle worms, no big deal. Today this fairly large tan thing with many legs (maybe 6 big, many more small) showed up crawling (?) on wall of refugium. It’s to the right of little snail - way bigger than anything else I’ve seen. Looks dangerous. Should I be worried?

 

[ScottR]

Looks like an anemone. Possibly aiptaisa, how fast was it crawling?

 

[ATAquariums]

Aiptasia

 

[Seaspirit]

I’ve seen a lot of aptasia, this isn’t that color and can move fast - swim - when startled.

 

[homer1475]

Possible hydroid? They tend to show up in newer tanks, and look alot like a tiny octopus.

 

[sfin52]

Aiptasia

Agree. Aiptasia can swim.

 

[Seaspirit]

Possible hydroid? They tend to show up in newer tanks, and look alot like a tiny octopus.

Hydroid is a really good guess - there are so many different kinds, they like calm water (barely any flow in this refugium) and they eat copepods, which I used to have a lot more of, come to think of it (sigh).

 

[Seaspirit]

Agree. Aiptasia can swim.

Thank you to all the aptasia votes, you inspired me to watch a video of aptasia swimming “startled” (which happens rarely, apparently). Even at top speed it’s relatively slow compared to this thing, which moves like a blur.