Adults only, in these images (one or more of the individuals in a loose aggregation or small school moving slowly along the edge of a Amphibolis antarctica meadow near old jetty).
Common on this dive and many were clearly awaiting cleaning (as were most of the other leatherjacket species seen, although I don't include the two smaller Acanthaluteres genus members in this general comment, and FWIW the subject Bluelined Leatherjacket above was foraging when I took the photo. )