Bull. nat. Hist. Mus. (Zool.) 59(1): 11-31 



Issued 24 June 1993 



Anatomy of the Melanonidae (Teleostei: 

 Gadiformes), with comments on its 

 phylogenetic relationships 



GORDON J. HOWES 



Department of Zoology, The Natural History Museum, Cromwell Rd, London SW7 5BD 



CONTENTS 



Introduction 11 



Materials and methods 12 



Abbreviations used in the figures 12 



Anatomy 13 



Neuromast pattern 13 



Infraorbitals 14 



Cranium 16 



Jaws 19 



Palatopterygoquadrate 20 



Hyoid arch 21 



Opercular bones 22 



Branchial arches 22 



Pectoral girdle 23 



Pel vie girdle 24 



Vertebral column and median fins 25 



Brain 27 



Swimbladder, viscera and body musculature 28 



Discussion 28 



Acknowledgments 30 



References 30 



Synopsis. The osteology and part of the soft anatomy of the gadiform family Melanonidae, represented by the 

 genus Melanonus Giinther, 1878, is described. Melanonus has several derived (autapomorphic) sensory features but 

 only three osteological ones. Although contained within the Gadiformes the family is excluded from both the 

 Macrouroidei and Gadoidei in lacking a modified palatine and enlarged intercalar and thus represents their 

 sister-group designated as the Melanonoidei. The Suborder Gadoidei now comprises two families of uncertain 

 phylogenetic affinity (Bathygadidae and Steindachneriidae) and two Superfamilies, Moridoidea and Gadoidea. 



INTRODUCTION 



The gadoid genus Melanonus Giinther 1878 contains two 

 species, M. zugmayeri Giinther, 1878 (Fig. 1), and M. gracilis 

 Norman, 1930, which together give a broad latitudinal, 

 circumglobal distribution (Cohen et al., 1990; Howes, 1991a). 

 Melanonus are relatively small fishes, the largest seen being 

 230mm total length and, oddly for gadoids, are meso- 

 bathypelagic (100-3000m). Outwardly, Melanonus resembles 

 a stomiatoid rather than a gadoid fish with its dark coloration, 

 large, strongly-toothed jaws and tapering body (Fig. 1). 



Until Marshall (1965) recognised (without diagnosis) a 

 separate family for the genus, Melanonus had been consid- 

 ered to belong to the Moridae. Marshall (1965) and Marshall 

 & Cohen (1973) contended that Melanonus was the most 

 primitive gadiform (anacanthine) fish, a contention based on 



the posterior position (at the forebrain) of the olfactory bulbs 

 and a relatively unmodified caudal fin skeleton. The features 

 Marshall & Cohen (1973) used to diagnose the Melanonidae 

 rested on soft anatomical features, viz. an elaborate system of 

 free ending neuromasts on the head and the corpus cerebelli 

 extending (forward) to the optic tectum. 



Apart from a few observations on the caudal fin skeleton 

 and gill-arches and a description of its cranial muscles (see 

 below) the anatomy of Melanonus has never properly been 

 described. Gosline (1971) complained that "No account of 

 the osteology is available. By contrast the family Gadidae has 

 received more attention from anatomists than almost any 

 other family of fishes". Despite these shortcomings several 

 assertions as to the phylogenetic position of the Melanonidae 

 have been made. 



Rosen & Patterson (1969) cited Marshall (1965; 1966) to 

 the effect that Melanonus represents a primitive gadoid. 



