What is this

Looks to me like it's possibly a single large button polyp on the sand.

 

Similar to this Palythoa mutuki polyp (zoanthid spp.)



Original article/picture credits: NatureScouter: Zoanthid Hunt (4-8 June 2008)

 

aiptasia? Why is it they're bad? I have a few in my overflow..... is it a major problem?

 

Aiptasia can multiply very quickly, they do not require a lot of food and will eat pods, they can photosynthesize and get quite large in size and numbers. They sting any corals they come into contact with and can sting fish/shrimp etc...

Once they have a foothold they are very difficult to irradicate! I am still fighting, using aiptasia x and peppermint shrimps but it's an ongoing battle.

 

oh dear god....this could be a problem...

 

Does it have a hard tube in the sand?

I agree, it does not quite look like aiptasia.

 

I would switch off your pump and remove your overflow then scrape the aiptasia off and rinse with plenty of RO water and that should remove them, if you just scrape and remove from the overflow whilst still in the tank they are likely to release planulas (offspring) into the water spreading them everywhere.

Where did they originally come from? They wouldn;t just appear on your overflow, they probably arrived on some live rock, if you do see some polyps on there I would recommend aiptasia x, but if there is no corals on the rock I would remove the rock and scrape them off then give that area of rock a quick RO rinse.

 

alright, good point... Ill check the corals see if theres any on the LR...

 

well whatever it is it ate two pieces of krill this morning and disappears into the sand sometimes.

 

I think you scored a free cerianthus

If you have bottom dwelling fish like scooter blennies or mandarins that can be an issue because they have a very powerful sting. With that said, people pay good money for cerianthus anemones.