What is that!! A R2R guide to common new tank hitchhikers.

[AcanSweeper]

Help ID please! Peanut worm hopefully?!

 

[Crabs McJones]

Help ID please! Peanut worm hopefully?!

The tentacles at the end make me think Medusa worm

 

[Reefkeepers Archive]

The tentacles at the end make me think Medusa worm

Yes, or some other kind of cucumber

 

[AcanSweeper]

The tentacles at the end make me think Medusa worm

Okay thanks! Quick google search says they're beneficial detritus eaters phew

 

[yasmin1208]

Hi guys, any idea what this could be? Never moved out of this spot but looks like a claw either opened or closed, just snapped shut when bristleworm went near. Any help greatly appreciated!

 

[OrionN]

Hi guys, any idea what this could be? Never moved out of this spot but looks like a claw either opened or closed, just snapped shut when bristleworm went near. Any help greatly appreciated!

That is a man-eating Moray!!!!
Kidding aside, I think it is a bivalve of some kind. Filter feeder.

 

[Crabs McJones]

That is a man-eating Moray!!!!
Kidding aside, I think it is a bivalve of some kind. Filter feeder.

Agree

 

[Fredinva]

My LFS found this lil critter a couple days ago just as he was about to dip some new coral. I'm even surprised he saw it at all at bottom of his container. When he showed me, i immediately said baby aiptasia.
NOT!
I went home and got my Jewelers loupe (5X).
it is about 1/8inch across, with about 12 or 13 arms(tentacles). It was firmly attached to the bottom of the plastic cup. But while taking a video, it crawled just like an octopus and moved about a 1/4 inch.
Ive done a bit of searching(googling) and cant find anything quite like it.
okay people, what ya think?
The video only shows 9 or 10 arms, but there are 12 or 13!!

 

[Reefkeepers Archive]

My LFS found this lil critter a couple days ago just as he was about to dip some new coral. I'm even surprised he saw it at all at bottom of his container. When he showed me, i immediately said baby aiptasia.
NOT!
I went home and got my Jewelers loupe (5X).
it is about 1/8inch across, with about 12 or 13 arms(tentacles). It was firmly attached to the bottom of the plastic cup. But while taking a video, it crawled just like an octopus and moved about a 1/4 inch.
Ive done a bit of searching(googling) and cant find anything quite like it.
okay people, what ya think?

I think we can safely rule out any arthropod, dosent look to be any hydroid I've ever seen, I don't think an anemone would get detached like that and it dosent appear to be a starfish of any kind. You have me stumped! It kinda looks like the feeding arms of something like a Medusa worm or other cuke, which would be my closest guess. @ISpeakForTheSeas @EeyoreIsMySpiritAnimal?

 

[ISpeakForTheSeas]

My LFS found this lil critter a couple days ago just as he was about to dip some new coral. I'm even surprised he saw it at all at bottom of his container. When he showed me, i immediately said baby aiptasia.
NOT!
I went home and got my Jewelers loupe (5X).
it is about 1/8inch across, with about 12 or 13 arms(tentacles). It was firmly attached to the bottom of the plastic cup. But while taking a video, it crawled just like an octopus and moved about a 1/4 inch.
Ive done a bit of searching(googling) and cant find anything quite like it.
okay people, what ya think?
The video only shows 9 or 10 arms, but there are 12 or 13!!

I think we can safely rule out any arthropod, dosent look to be any hydroid I've ever seen, I don't think an anemone would get detached like that and it dosent appear to be a starfish of any kind. You have me stumped! It kinda looks like the feeding arms of something like a Medusa worm or other cuke, which would be my closest guess. @ISpeakForTheSeas @EeyoreIsMySpiritAnimal?

Looks like it may be a very small Swimming Anemone, Boloceroides mcmurrichi. For a fairly similarly sized specimen to compare with:

The Biodiversity of Singapore

 

[Reefkeepers Archive]

Looks like it may be a very small Swimming Anemone, Boloceroides mcmurrichi. For a fairly similarly sized specimen to compare with:

The Biodiversity of Singapore

I'll remember that for next time! Forgot about swimming nems

 

[Fredinva]

hey, ispeakfortheseas!!! you may have something there, i will check further tomo.
thanks

 

[djohnson610]

Great writeup! Didn't realize hydroids were considered bad. See them from time to time on my glass...but very few at that. Why are they bad?

Hydroids are predatory. Related to jellyfish and can sting fish and corals.

 

[vetteguy53081]

My LFS found this lil critter a couple days ago just as he was about to dip some new coral. I'm even surprised he saw it at all at bottom of his container. When he showed me, i immediately said baby aiptasia.
NOT!
I went home and got my Jewelers loupe (5X).
it is about 1/8inch across, with about 12 or 13 arms(tentacles). It was firmly attached to the bottom of the plastic cup. But while taking a video, it crawled just like an octopus and moved about a 1/4 inch.
Ive done a bit of searching(googling) and cant find anything quite like it.
okay people, what ya think?
The video only shows 9 or 10 arms, but there are 12 or 13!!

hydrozoan and will move about the tank. Catch it and discard

 

[bambooshark]

Great guide, but can you include more information on how to get rid of ther bad ones? Like how to trap fireworms?

 

[nano7g]

Maybe this can be included in the guide?

Not a common hitchhiker but this showed up in my tank and was finally ID'd as Dinophilids in another thread. I know of only one other poster who had this as well. Looks and moves like a flatworm but has a segmented body. Is NOT a flatworm. Interstitial annelid about 1mm in length and among the tiniest animals. Good hitchhiker. Feeds on detritus, bacteria, protozoa, unicellular algae and diatoms.

 

[Irondynamics]

How common is it to have a single zoanthid eating spider in your tank? I removed one the other day, and am worried there may be others. I have looked and looked and can't seem to find any. Really hoping it was a single hitchhiker

 

[ISpeakForTheSeas]

How common is it to have a single zoanthid eating spider in your tank? I removed one the other day, and am worried there may be others. I have looked and looked and can't seem to find any. Really hoping it was a single hitchhiker

There's a good chance there was only the one - if you've got eggs or a breeding pair, then that's a problem though.

I'd say to keep a close eye out and check how your corals are doing; most pycnogonids (zoa eating spiders are a kind of pycnogonid) are nocturnal, so you may need to check at night for them.