28 



& Crimmen (1990) and of those published descriptions Breg- 

 maceros has the most similar overall morphology. Like that 

 of Melanonus the brain is elongate with extensive trigeminal- 

 facial lobes, a long cerebellar crest and closely connected 

 olfactory bulb and lobe. However, there are major differ- 

 ences in the relatively small size of the olfactory and inferior 

 lobes and in the cerebellar corpus being orientated posteri- 

 orly along the crest, having a posterolateral fissure and 

 leaving the midline of the optic lobes exposed. 



Anterior placement of the forebrain was considered a 

 gadiform character by Svetovidov (1948) and among gadoids 

 there is a tendency for the brain to be shifted forward. In 

 those few morids investigated and in macrouroids the fore- 

 brain is generally confined to the cranial cavity. In some other 

 paracanthopterygians (ophidiiforms, Howes, 1992 and per- 

 copsids pers. obs.)the telencephalon lies in the orbital cavity 

 as in Melanonus. 



It is problematic as to which features of gross brain 

 morphology can be used as phylogenetic markers. The degree 

 of separation of the olfactory bulb from the lobe is variable in 

 gadiforms (discussed by Howes & Crimmen, 1990) but the 

 plesiomorph condition, possessed by Melanonus, is seemingly 

 for them to be closely associated. The shape of the olfactory 

 lobe is also a highly variable feature and one that might, at 

 least, be generically characteristic. 



Summarising data from gadoid brain descriptions given by 

 Svetovidov (1953) it appears that elongate and short cerebral 

 crests are equally distributed amongst the taxa he studied. A 

 short, tall cerebral crest, common to gadoid brains, is also the 

 common condition among paracanthopterygians. However, 

 the granular eminence, although often large is laterally 

 extended only in the Gadidae (sensu Dunn, 1989 and Howes, 

 1991b). 



Swimbladder, viscera and body musculature 



(Fig. 17). 



The swimbladder is an elongate ellipsoidal, thin-walled sac 

 adhering tightly to the vertebral column apart from where the 

 long bilobed kidney runs on either side of the midline. 

 According to Marshall & Cohen (1973) the melanonid swim- 

 bladder is reduced and there are two retia. In the specimens 

 of M. zugmayeri examined for this feature, the gas-gland 

 covers nearly two-thirds of the anterior floor of the sac and 

 there are four retia supplying separate lobes. Posteriorly the 

 gas-gland tapers and is deeply pocketed. The oval appears to 

 be beneath the retial area. 



The stomach is siphon-shaped, exceptionally thick-walled 

 with a deeply and much convoluted mucosal membrane; 

 there are six or seven caeca lying ventrally; the intestine is 

 long and double-bended. The bilobed kidney is extensive, 

 almost enveloping the stomach. The gonads lie posteriorly on 

 either side of the swimbladder to which they are attached by 

 thin strands. 



The anterior body musculature is similar to that described 

 for Bathygadidae (Howes & Crimmen, 1990) except that 

 melanonids lack the same degree of differentiation between 

 dorsal and ventral sections of the epaxialis musculature (Fig. 

 17), the dorsal section being apparent only anteriorly (the 

 general condition) and not extended as far posteriorly as in 

 bathygadids. 



Fig. 17. Melanonus zugmayeri anterior body musculature and 

 visceral cavity dissected on the right side; the anterior part of the 

 liver has been cut away to expose the pyloric caeca and the 

 swimbladder has been dissected. 



DISCUSSION 



Melanonus has undoubtedly derived sensory features; the 

 brain has a unique morphology amongst paracanthoptery- 

 gians, extending well forward into the orbital cavity, the head 

 is covered with a unique type and pattern of open-ended 

 neuromasts innervated by the ramus canalis lateralis of the 

 trigeminal nerve, the RLA nerve being absent. In its cranial 

 osteological characters three can be considered derived: the 

 shape of the fifth infraorbital, and exclusion of the supraoc- 

 cipital from contributing to the foramen magnum. The first 

 two of these osteological characters are autapomorphic; the 

 enlarged pterosphenoid is undoubtedly correlated with the 

 anterior position of the telencephalon. The third is a feature 

 shared with ophidiiforms, in that group, however, the exoc- 

 cipital is expanded dorsoposteriorly so as to exclude most of 

 or the entire supraoccipital from the rear of the cranium and 

 from contact with the first neural spine. In melanonids the 

 supraoccipital is excluded from the border of the foramen 

 magnum by its failure to extend ventrad during development, 

 but nevertheless it still forms the upper posterior border of 

 the cranium and contacts the first neural spine. 



Aside from these autapomorphies there are no other 

 apomorphies which are shared with other gadoid taxa. The 

 diagnosis of 'Gadoidei' has proved difficult since most syn- 

 apomorphies so far proposed are either not exclusive to, or 

 their distribution has not been completely documented, in the 

 taxa currently embraced under this category (see below). 



Howes (1990; 1991a; 1991b) proposed a series of gadoid 

 clades of which 'supragadoids' were recognised on the basis 

 of a fused upper hypural plate of the caudal skeleton. A 

 sequence of other synapomorphies, including an interopercu- 

 lar fossa, contact of the posterior face of the lateral ethmoid 

 wing by the first infraorbital and reduction of pterygoid bones 

 (Howes, 1990) excluded Melanonidae from this group. Other 



