on the last pic of the juvie pics , that looks like ocellated spot on fin , which would indeed make it marulioides as C. melanopterus never has this .
for phen_dox - marulioides and melanopterus have allmost the same characteristic ,ie ray and scale counts , also because there are many diferant variations in marulioides ,that is what makes the id hard there are many base colour variations in marulioides from diferant locations, as you know many marulioides get the very distinct flower pattern like maurlius , but not all get this , when they lack the flower pattern i.d becomes harder , (allough i think i see slight flower on fish in question) so then iam looking for any other slight diferances between the two , the only obvious diferance is the ocellated spot in which is useally observed in juviniles and sometimes disapires with age , again i think i see the spot in the last pic , since melanopterus does not get a ocellated spot at all , that would be another identifier
unfortunatly my pics are not clear enough to show fin ray counts , but heres a couple of pics anyway
psuadomarulia - you can see here the blatent diferance in head shape to marulioides and melanopterus
marulioides - juvie without ocellated spot - but you can see head shape same as fish in question
maruila - really poor photo showing ocellated spot and again diferant head to marulioides (marulioides eyes lot closer to mouth)
unfortunatly i have never kept melanopterus
marulioides ray count - unfortunatly , as you can see from this figure the figures for all 3 over lap , unfortunatly my pic is no where near good enough to show the other counts
hope this is what you where after
cheers col