Black Sea Cucumber Identification

[chuckdylan]

I purchased what I believed to be a black spiny cucumber about 5 weeks ago. I got it to sift sand, as suggested by an employee at the shop. In 5 weeks it has not even touched the sand. It just slowly does laps around the glass at the top of the tank. In the pic you can see what kind of look like filter feeding appendages but it seems to use them to feed off pods and algae on the glass. It is all black and I thought the filter feeders were all colorful. Can anyone identify?Will this guy ever sift sand? I think it won't get enough food if it is a filter feeder.

Thanks guys

[chuckdylan]

In the past 5 weeks I have tried placing it on the sand and it just climbs right back up the glass each time. All other inverts in the tank seem to be doing great.

[Spartan]

It doesn't look like a filter feeder. I have one that looks very similar. It occasionally hangs out on the rocks or glass for several days. I think eventually it will settle down. Are you water parameters ok?

[Betta132]

What size tank? What else is in there?

[chuckdylan]

Water parameters are all good. 48 gallon mixed reef with various LPS and SPS all doing great. There have not been any fish in the tank for around 6 weeks and it is very clean, so the cucumber might not like that. There are about 8 smallish hermit crabs that I feed every day but maybe not enough. I have not seen them bug the cucumber but maybe he stays on the glass because the crabs are trying to snack on him. Do cucumbers eat algae off the glass?

[Betta132]

Most cucumbers eat assorted gunk off the sand. They're scavengers who can't be kept in clean tanks, or smallish tanks like yours. Could be he's slowly starving.
You don't want something like a cucumber that's going to sift your sand like that, it'll eat all the useful stuff. Nassarius (probably misspelled that) snails will turn the sand over a bit without eating your useful critters.

[Amphiprion]

It looks like the type to sift sand. If it is remaining at the top, there is either too little food or the sand grains are not to its liking--could be too large, as these guys can be picky.

These do not deplete a sand bed of beneficial fauna. They consume biofilms and algal coating on sand grains, along with some detritus--and often need quite a bit of it.

[chuckdylan]

Thanks for the replies everyone. I will try and find a better home for it. Does anyone have experience with a cucumber like this dying? Does it "nuke" the tank? Or to phrase it differently; does it release more toxins then a dead fish of the same size?

[Amphiprion]

Never had one of these cause a problem beyond the typical decay, but I've only lost two in a very long time. One met its fate in an old maxijet powerhead and the other withered away silently--never noticed it was gone until after a couple of weeks.