Whatever it is I have no memory of adding it (Maybe). This TBS rock has been with me for a long time. I added a Ricordia years ago & it just disappeared so thought it was long gone. This was 2 tanks & a sump for years later then 3 years in this 75. It just might be the same. the critter in question is just left of center . There are 5 other smaller one to left & right. there is a magenta ring maybe? Sorry for the poor picture. This was the best out of a bunch ! Thanks