ID this thing

[PufferGuy]

Well i found this crawling on my glass today and i have no clue what it is... closest thing i can compare it to is a sea cucumber?

 

[yote]

Looks like a cucumber to me too.
Cool hitch hiker:D

 

[PufferGuy]

so leave him in there? can any harm come from this guy?

 

[yote]

From my understanding,they just feed on detritus and algae.I'd leave him alone.