Thought this was Algae but it has tentacles!!

[Fl_Seagull]

At first I thought the branched flexible stick growing up from the rock was Halymenia sp. But it has small tentacles like a feather duster at the end of the "branches". Also, the end of the branches are blue-green when the tentacles are out. It is speading. Could this be a Hydroid?

 

[John_Brandt]

Could this be a Hydroid?

Maybe. But you have to provide us with a good, focused close-up photo, please.

 

[Fl_Seagull]

This is the best I am able to do with my current camera. Sorry.

 

[John_Brandt]

Too bad you can get a closer picture.

Is the branched structure flexible or hard and brittle? Do the "tentacles" retract when you touch them?

You say it is spreading. Do you mean more "twigs" are sprouting from the branches? Or, more of these things are sprouting from the rock?

 

[Fl_Seagull]

The branched structure is flexible and about 1/32" dia. The new "twigs" are translucent. They are sprouting from the branches and from the rock surface. Some are on the base rock. I think this was from a fragment of the original.

The "tentacles" retract when I touch them. They appear to be closer to the tops of small feather dusters VS true tentacles.

One more attempt at a picture:

 

[John_Brandt]

Fascinating! It's a red macroalgae, probably Galaxaura or Gracilaria. There may be fan worms or hydroids living upon it. Do the "tentacles" retract instantly after contact? Does it look like little animals living on the algae, or what?

 

[Fl_Seagull]

Thanks for the insight.

I pulled the rock out of the tank to get a closer look. Some (most) of what I thought to be tentacles was hair algae .

Where I touched and saw the tentacles retract has several small feather dusters hidden in among the algae. Also, the algae has several twigs, near the base, which look different -- more white which have retracking tentacles. These branches look like the tubes of small feather dusters else where on the rock. There is also a whitish thin branch with several twigs that have non-retractable "tentacle".

Except for various "pods" caught in the hair algae, I did not see any other animals on the branches.

 

[Anonymous]

good call John i agree it looks like Gracilaria however im no expert on IDing Algaes...

 

[John_Brandt]

It can be quite difficult to ID algae. Marine algae take on many different colors and shapes depending on the conditions they are living in.

As you can see from the two photos, the early growth form can differ dramatically from the older plant. This is especially true with the red algae family.

I'm not at all certain what algae this is, but my first choice is Gracilaria.

 

[Anonymous]

ive had Gracilaria thats why i kinda agree with you on the other hand you are right on the second note with IDing algaes and plants...