Mini species ID

HI, I know there is a mini species id pdf on here, I even have it downloaded and find it very helpfull, I'm just not 100% about this one. Was out with mick yesterday and while he was busy catching ray I couldn't seem to get past the dogs so decided to have a go down under my feet to see if anything about. This guy was about 13cm long and I reckon could be a black goby, but one peculiarity not mentioned on the mini species pdf was an unusual fan like fin on the underside hinged not along but across the body, any help appreciated

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A black goby

What Donal said

yup yup chalk it down