What are these?

[Charles Belisle]

I am moving from 40 gallon into 240 gallon - while pulling rock I noticed these back spots under the rocks- see pics - are they harmful? What are they?

 

[Charles Belisle]

I am moving from 40 gallon into 240 gallon - while pulling rock I noticed these back spots under the rocks- see pics - are they harmful? What are they?

They look like small spot of oil / maybe leech like.

 

[sfin52]

A type of sponge

 

[Charles Belisle]

A type of sponge

Ahh would make sense - I have white/clear sponge growing in tank as well - so nothing to worry about. Thanks

 

[sfin52]

Ahh would make sense - I have white/clear sponge growing in tank as well - so nothing to worry about. Thanks

Nope not a problem at all. In fact some try to get these to grow in a cryptic refugium.