good starfish? bad starfish? id help

[Frigideus]

saw this guy, and he looks like a micro brittle. however its been riding on top of this margherita snail for the past 24 hours and it looks like there is a hole in its shell now. should i get rid of this starfish?

my tank is very new and going through the uglies right now so please try and ignore it. hopefully a water change and some all-for-reef this weekend will help alleviate it. :)

 

[Sophie"s mom]

Looks like a micro brittle star to me for sure. I have never heard of them doing this, but let's see if someone else can come in with more info.

 

[Frigideus]

hope someone has the answer, but thank you! i just dont want to wake up one day and find all my snails eaten

 

[Troylee]

Looks like a micro brittle but maybe it’s not! Seems a little big so I’m not sure.. @ISpeakForTheSeas

 

[ISpeakForTheSeas]

Looks like a micro brittle star to me for sure. I have never heard of them doing this, but let's see if someone else can come in with more info.

Looks like a micro brittle but maybe it’s not! Seems a little big so I’m not sure.. @ISpeakForTheSeas

Very interesting- I haven't seen this before.

If the hole just appeared overnight, then it seems plausible the star may be attempting to bore into the shell, but that would be bizarre behavior by all accounts I've heard (I can't seem to find any source indicating Ophiuroids - brittle and serpent stars - bore into rocks or shells) and would require a very specific, repetitive motion for it to form a crater like that.

As a note, these don't have eversible stomachs like true starfish do, and I haven't heard of these having any real chemical capabilities (a chemical alarm defense mechanism is the most I know of at the moment), so it would have to be causing this mechanically if it is really to blame. Also of note, I have only heard rumors of large (and known predatory species) brittle stars hunting snails (presumably as a kind of famine food), so I find it extremely unlikely that a little star like this would be trying to hunt the snail.

I would say try and get some very good close up pics of the star's central disk (top and bottom) and legs (particularly of the spines on the legs starting about halfway down the limb and moving in towards the central disk) - then I would try just placing it on your rock-work and seeing what it does after that.