The colour can be greenish or orange with light blue spots and there is a white line along the back.

[2] Opeatogenys gracilis occurs only in the northeastern Atlantic Ocean from the coasts of the Algarve eastwards to the Levant.

Within the Mediterranean, O. gracilis has been recorded off the coast of Malaga, Spain, Algeria, Cyprus, France, Sicily and off Sfax in Tunisia.

[1] Opeatogenys gracilis is found on the leaves of seagrasses such as Posidonia oceanica and Cymodocea nodosa and on the fronds of algae, attaching to the leaves or fronds with the sucking disc formed by the modified pectoral fins.

It was originally described as Mirbelia gracilis by Giovanni Canestrini from a type locality given as the Mediterranean Sea.