I have this little slug or snail(It looks like a snail with out a shell)It has a flat kind of shell.
I think it is called an Abalone.
Today it was squirting out tiny yellow things out of it's shell.Was it releasing babies?My fish seemed to eat them up.
It is possibly a stomatella snail. You can google for more info, but I am fairly sure they are harmless. I have a few in my tank (nice variety of shells) and have not seen problems with them.
+1 on the stomatella ive got a few and every once in a while i catch them sprayin like a cloud i believe its just them going sexual havent cought them releasin eggs tho, but there a nice grazing hitchhiker