ID please [VIDEO]

[acabgd]

Anyone knows what this is? Is it good or bad?

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[tektite]

Either some type of nudibranch (may be neutral or bad) or possibly a polyclad flatworm (bad)

 

[biocube14g]

It's a nudibranch, but of what kind, I don't know.... Some are good, some are bad... Maybe someone else can chime in.

 

[leveldrummer]

my vote goes to polyclad flatworm too...