Benthic amoebic thingy.

[ptychoptera]

I have a couple of these strange beasties on my glass. One is around a centimeter in diameter and the other 4mm or so. They are quite flat (protruding not more than a millimeter or two) and don't seem to possess the tentacles one would expect from a ctenophoran. The closeup photo seems to show some kind of irregular internal tubing, for lack of a better term. Movement is in an amoeboid fashion and imperceptibly slow.

Ctenophora was the first thought that popped in my mind, but the apparent lack of tentacles leads me to question that. I briefly considered placozoa, but the large size and internal complexity seem to rule that out. So I'm left with this being some kind of giant marine amoeba.

Anyone have a better ID than that?

Note: This specimen is around 4mm. Photos taken with and without flash; the brownish color is from the flash.

This last photo illustrates its manner of locomotion; the two photos were taken about an hour apart.

 

[ptychoptera]

Here's an animation I made over the course of one hour. Notice the definite clockwise rotation and changing perimeter.

For a slightly larger version go here http://www.nano-reef.com/forums/index.php?showtopic=134889

 

[LeslieH]

I would have agreed with you about ctenophoran, the underside of a benthic ctenophore in fact. Keep checking for 2 long pinnate tentacles which are reeled out from 2 areas on the other side then reeled in again when disturbed or a copepod is caught. Another possibility is newly settled cnidarian planulae.

 

[graveyardworm]

I'm gonna go with newly settled cnidarian. Any chance you have Pocillopora Damicornis in your tank? Here's a couple photos of one of mine awhile back.

 

[rabidcrab]

sum type of flat worm?

 

[ptychoptera]

Thanks for the ideas everyone. I'm leaning towards this being a Pocillopora damicornis planula. I noticed several small colonies of it when I collected the rock these guys hitched in on. I'm taking more time lapse stuff and will update when I figure it out.

 

[ptychoptera]

<a href=showthread.php?s=&postid=11054031#post11054031 target=_blank>Originally posted</a> by ptychoptera
Thanks for the ideas everyone. I'm leaning towards this being a Pocillopora damicornis planula. I noticed several small colonies of it when I collected the rock these guys hitched in on. I'm taking more time lapse stuff and will update when I figure it out.

EDIT: A few hours after I turned the lights out I observed a tentacle dangling from the larger specimen. Mystery solved.

Though I'm now curious why this little ctenophoran is rotating. My latest time lapse revealed that it also changes its rotational direction.

 

[LeslieH]

Legs cramps? Seriously, we just don't know. Based on my experience with live ones some do and some don't.

 

[aninjaatemyshoe]

What did you take the pictures with? You obviously have one rather nice camera setup.

 

[ptychoptera]

Thanks. It's actually a rather cheap set-up. A Canon Powershot S2 IS with a Raynox macro lens. I don't even own a tripod, which is why the depth of field is a bit off on such a flat creature. For the time lapse stuff I had the camera propped up on some books.