Small red sea cucumber?

[napalms]

Found this small red (sea cucumber?) On the sandbed

For some extra context the grid its on is 1x1 cm its in a 200L aquarium with 4 seahorses, i dip all my coral but didn't dip my macro algae (also once a gorgonian with a small red tree sponge was added to the aquarium with out dipping because i wasn't home to receive it), the last time i added anything to my aquarium was atleast 3 months ago and nothing has died since (although mu flatworm issues has gone away?) Its about 2,5cm long (1inch) and it has a butt shape on both ends.

If its harmless id like to add it back to the tank but id like to know what it is

 

[napalms]

Oh and its definitely alive and moving

 

[napalms]

Also its not stuck on surfaces like you would expect a snail to be its more walking /crawling ontop

 

[IKD]

I don’t know do any cucumbers that are bad for a reef tank. Usually the filter-feeding types don’t survive due to not meeting nutritional needs. If yours has been with you for months (at least), and you haven’t noticed any issues, I would place him back. Can you tell if he’s feeding by consuming sand or filter feeding from the water column?

 

[napalms]

I don’t know do any cucumbers that are bad for a reef tank. Usually the filter-feeding types don’t survive due to not meeting nutritional needs. If yours has been with you for months (at least), and you haven’t noticed any issues, I would place him back. Can you tell if he’s feeding by consuming sand or filter feeding from the water column?

Im guessing the sand type because i haven't seen him extend anything to filter feed and he was found on the sandbed