ANATOMY OF THE MELANONIDAE 



15 



Fig. 3. Infraorbital bones of M. zugmayeri in specimens of: A, 66mm SL; B, 100mm SL and C, 130mm SL. 



posteriorly, the body of the bone is expanded. The fifth 

 infraorbital has a long orbital margin, the lower part of which 

 projects anteroventrally in front of both the third and fourth 

 to which it is connected by strong connective tissue; it has a 

 narrow flange along its upper orbital border. The sixth 

 (dermosphenotic) is as large as the fifth and has a pronounced 

 orbital curvature which brings its anterior tip to the same 

 vertical plane as the ascending process of the first infraor- 

 bital. 



In the two smaller specimens of M. zugmayeri examined, 

 the dorsolateral flange remains undeveloped on the first, fifth 

 and sixth infraorbitals of the 66mm specimens and the 

 ascending process of the first infraorbital is inclined anteriorly 

 in both (Fig. 3A). The anteroventral border of the fifth 

 infraorbital is less pronounced and in the 100mm SL speci- 

 men its tip lies medial to the rim of the fourth infraorbital; the 

 sixth lacks the anterior elongation of the larger (130mm SL) 

 specimen (Figs 3B, C). 



Unlike other gadiforms where the posterior (fifth and 

 sixth) infraorbitals are shallow, those of Melanonus are as 

 deep as the anterior ones. The anterior curvature of the 

 upper infraorbital (dermosphenotic) is more reminiscent of 

 some macrouroids (see below) than gadoids. The central 

 position of the ascending process of the first infraorbital is 

 probably a plesiomorphic gadiform feature (on the basis of 

 commonality) as is the reduced size of the second infraor- 

 bital. The extension of the lower part of the fifth infraorbital 

 and the enlargement of the dermosphenotic are, because of 

 their restricted distributions, taken to be derived features. 

 According to Iwamoto (1989) among macrouroids, exclusion 

 of the third and fourth infraorbitals from the orbit is a derived 

 condition. In Melanonus similar exclusion has resulted from 

 ventral extension of the fifth infraorbital whereas in the 

 macrouroids illustrated by Iwamoto (1989, fig. 5G) it is due 

 to re-alignment of the fourth infraorbital which covers the 

 orbital borders of the second and third. 



