Please help me ID this thing growing on my octospawn!

[dward0487]

Alright, so I've been trying to figure out what's growing on my octospawn, and I just can't seem to ID this thing... It is a semi-circular growth that seems to be "soft" compared to the hard skeleton of the branching octospawn. You can actually see it swell and contract over time. It basically gains height off the surface of the branch and then flattens out. It also has little fine "hairs" around its edges, similar to the little strands that I see on the bodies of my trochus snails. Here are a few pictures:

I took this one with the flash on so you could see the difference in color between it and the branch of the octospawn.

This is the best shot I could get of the little "hairs" contrasting against the back wall of my tank.

Here's a rough drawing I made to show how it swells up and contracts:

Upon closer inspection, the surface of this thing is hard, but the sides must be soft. I touched it with my coral feeder tube and it immediately went flat against the branch.

Here's a slightly better shot I took, trying to show it in its "raised" state, with the hairs visible:

I tried to outline the general shape in red. It seems almost "hinged," in that the left side raises up, while the right side stays fairly flat. In a way, it resembles a clam or scallop.

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If any of you know what this thing is, please tell me! My octospawn hasn't been extending very much lately, and I'm worried it might be some sort of pest/parasite that may be causing it. Thanks!

 

[dward0487]

Nobody?

 

[PL-Reef]

Octospawn? Never heard it called that before.

 

[dward0487]

Well, it's short for "octopus frogspawn." They have smaller and more numerous colored bubbles running down the length of their tentacles than a standard frogspawn.

 

[Steveb]

barnacle?

 

[sublime9182]

I'm no expert but it looks like where a head was previously broken off?

 

[dward0487]

I considered the idea of it being a barnacle, but I don't see the little hole that you usually see on barnacles... And it's definitely not the site of a previous head. This thing is alive. It "opens" and "closes" (rises up and down) in response to current or stimulation. I tried to see up under the little shell from a different angle, and it looks like there's a "spine" inside it. A central line with little "ribs" on both edges.

Here's the shot of the spine along the inside of the shell:

 

[mayjong]

oyster or clam of some sort?

 

[Reef Bass]

Interesting. I'd have to agree there is some sort of animal attached to your octospawn. Possibly a chiton variant? If no one here knows, I'd try running a pic by an invertebrate biologist at a local university.

 

[ecksreef]

Abalone?

 

[OrionN]

Does it move? It may be a small oyster (or one of the bivalves that permanetly attached)

 

[dward0487]

Yeah, it hasn't moved around on the branch at all since I got the coral.

 

[Tweaked]

A dip didn't kill it?

 

[OrionN]

It is an oyster, likely not one of the species that we eat, but an oyster nevertheless.