Mystery Hydroid

GaleB · Sep 27, 2022

I observed this critter in one of my store tanks for about two months. I have unfortunately moved and never managed to get better photography so I'm afraid this will have to do. I'm just fascinated by them because I have not been able to ID them for months! I have collected a couple other posts that contain pictures of something that looks similar— so far, positive ID has not been offered in any of those threads. They seem pretty rare compared to digitate and medusa hydroids. Whats unique about this animal is that each polyp has a holdfast, as opposed to other branching hydroids which have colonies that extend out into the water. Perhaps this body format is an early stage of those other hydroids? Flow too high to risk forming an appendage?
I'm starting to worry that this species has only been observed in the hobby and hasn't been named because we are all too concerned with killing it! I have been sharing with my biologist/aquarium friends and none of them have seen anything like it.

If you have had these guys or ever attempted a similar ID I'd love to hear about it.

Looks like it might be my guy:
https://www.reef2reef.com/threads/hydroids.888316/#post-9841025 https://www.reef2reef.com/threads/potential-hydroids-taking-over.886178/http://www.wetwebmedia.com/hydrozoanfaqs.htm
Kinda like my guy but with detached polyps:
https://www.reef2reef.com/threads/branching-or-colonial-hydroids.735920/https://www.reef2reef.com/threads/hydroid-id.359360/

vetteguy53081 · Sep 27, 2022

GaleB said:
I observed this critter in one of my store tanks for about two months. I have unfortunately moved and never managed to get better photography so I'm afraid this will have to do. I'm just fascinated by them because I have not been able to ID them for months! I have collected a couple other posts that contain pictures of something that looks similar— so far, positive ID has not been offered in any of those threads. They seem pretty rare compared to digitate and medusa hydroids. Whats unique about this animal is that each polyp has a holdfast, as opposed to other branching hydroids which have colonies that extend out into the water. Perhaps this body format is an early stage of those other hydroids? Flow too high to risk forming an appendage?
I'm starting to worry that this species has only been observed in the hobby and hasn't been named because we are all too concerned with killing it! I have been sharing with my biologist/aquarium friends and none of them have seen anything like it.

If you have had these guys or ever attempted a similar ID I'd love to hear about it.

Looks like it might be my guy:
https://www.reef2reef.com/threads/hydroids.888316/#post-9841025 https://www.reef2reef.com/threads/potential-hydroids-taking-over.886178/http://www.wetwebmedia.com/hydrozoanfaqs.htm
Kinda like my guy but with detached polyps:
https://www.reef2reef.com/threads/branching-or-colonial-hydroids.735920/https://www.reef2reef.com/threads/hydroid-id.359360/

Colonial hydroids and hydrazoa

ISpeakForTheSeas · Sep 28, 2022

The fact that it's only growing polyps on side of the branch (i.e. all of the polyps seem to be growing upwards in the photo) is interesting to me, as all of the similar specimens that I know have polyps growing on both sides of the branch (top and bottom). I don't know if that's because it's a young specimen in your photos or if it just grows like that regardless of age, but it's definitely interesting.

That said, here are some similar specimens that - if nothing else - might give you a place to really start you search for the species:
- Eudendrium (genus) [this one would be my guess, but I'm definitely not a hydroid expert]
- Bougainvillia (genus)
- Turritopsis (genus) [a few of these look similar, most of them don't]

Alternatively, you might be able to reach out to a hydroid special (like Joan J. Soto-Angel, who you can find on Twitter and Instagram) and see if they could help you ID it. Sometimes professionals are open to helping, sometimes they're not. I've found it helps if you remain respectful/professional with them but also let them know you're genuinely interested in/excited by the topic you're asking them about (but it's still not guaranteed that they'll help/get back to you).

Good luck on your search, and welcome to Reef2Reef!

GaleB · Sep 29, 2022

ISpeakForTheSeas said:
The fact that it's only growing polyps on side of the branch (i.e. all of the polyps seem to be growing upwards in the photo) is interesting to me, as all of the similar specimens that I know have polyps growing on both sides of the branch (top and bottom). I don't know if that's because it's a young specimen in your photos or if it just grows like that regardless of age, but it's definitely interesting.

That said, here are some similar specimens that - if nothing else - might give you a place to really start you search for the species:
- Eudendrium (genus) [this one would be my guess, but I'm definitely not a hydroid expert]
- Bougainvillia (genus)
- Turritopsis (genus) [a few of these look similar, most of them don't]

Alternatively, you might be able to reach out to a hydroid special (like Joan J. Soto-Angel, who you can find on Twitter and Instagram) and see if they could help you ID it. Sometimes professionals are open to helping, sometimes they're not. I've found it helps if you remain respectful/professional with them but also let them know you're genuinely interested in/excited by the topic you're asking them about (but it's still not guaranteed that they'll help/get back to you).

Good luck on your search, and welcome to Reef2Reef!

Thank you SO MUCH, you rock!!! I will update this thread with any findings.