Some kind of worm?

[keithwalk]

Hey. Can someone please identify these little creatures for me. They hitchhiked in on some chaeto I purchased. (It’s only in the display tank temporarily)

 

[EeyoreIsMySpiritAnimal]

Probably going to need a photo under white lights

 

[ISpeakForTheSeas]

Welcome to Reef2Reef!

Those are Zancleid/Digitate Hydroids:

Not sure on the black dots (probably a pod of some variety, but microscope pics would be needed to say for sure). For the string though:

Those are Digitate Hydroids (definitely a Zancleid hydroid [taxonomic family Zancleidae], possibly a Zanclea sp.) - there's evidence to suggest that they're actually beneficial to the corals they grow on;* I don't know if they'd sting fish that get too close or not, but it is a risk - similarly, they may spread and cause issues by growing too numerous in the tank and possibly posing a risk to other tank inhabitants.

I know @Reefkeepers Archive had a colony of these - I don't know if they've caused any problems for them or not, but if they still have the colony, they'd have ~5 months of experience with them to relate.

*Source:

https://www.researchgate.net/publication/321938186_Corals_hosting_symbiotic_hydrozoans_are_less_susceptible_to_predation_and_disease

It's generally suggested to get rid of hydroids, as they (like many corals) have stings - if the species has a potent enough sting, it can cause problems for you and your tank inhabitants.

There are a few species (like at least some of the Zancleid species mentioned above) that seem potentially harmless/worth keeping, but many are problematic, so removal at this point is the safer option.

 

[Reefkeepers Archive]

Welcome to Reef2Reef!

Those are Zancleid/Digitate Hydroids:

Second digitate hydroids. Can be harmless/beneficial but can also be problematic...