ANATOMY OF THE MELANONIDAE 



25 



Vertebral column and median fins (Figs 13-15) 



There are 12-14 abdominal and 45 or 46 caudal (those with 

 closed haemal spines) vertebrae in Melanonus (Fahay & 

 Markle, 1984 give total counts of 58-62 for the genus). The 

 first neural arch and spine are well-developed and form an 

 ankylosed unit with the centrum. The prezygapophyses of the 

 first vertebra (Fig. 13A) are oval in section, hollow and 

 cartilage-filled and firmly in contact with the similarly shaped 

 paired condyles of the exoccipital. The wall of the neural arch 

 covers the upper posterior wall of the exoccipital leaving 

 exposed a notch through which pass the occipital and lateral 

 line nerves (Fig. 7B). The laminae of the neural arch extend 

 forward to embrace the posterior extension of the supraoccip- 

 ital crest (Fig. 7A). The second vertebra is anteroposteriorly 

 compressed and lacks processes or ribs; the third-fifth verte- 

 brae support successively shorter chopstick- shaped ribs 

 which extend almost horizontally, at their tips lie epipleural 

 (epineural) ribs the heads of which are ligamentously 

 attached to their respective myosepta (Fig. 13B,C). The 

 sixth-twelfth centra bear triangular parapophyses to each of 

 which is attached a posteriorly curved epipleural rib. Accord- 

 ing to Okamura (1989) there is a total of eleven epipleural 

 ribs in Melanonus; ten are counted here in M. zugmayeri. 



There is a single dorsal fin comprising 72-78 rays. The first 

 dorsal ray is often minute, the second and successive rays are 

 long and flexible, supported by distally tapered rod-like 

 radials which tend to occur in pairs within each interneural 

 space, their proximal tips converging (Fig. 13C,D). The 

 origin of the dorsal fin occurs between the third and fourth 

 neural spines. There are no supraneurals (predorsals). The 

 anal fin has 50-58 rays and lacks a stout anterior spine; the 

 shape of the radials is similar to those which support the 

 dorsal fin (Fig. 13D). 



Caudal fin skeleton (Fig. 15A,B). The caudal fin skeleton 

 of Melanonus resembles that of the Moridae in that the first 

 and second hypurals are incompletely fused; each support a 

 single fin ray. In morids all the hypurals are fused only 

 proximally whereas in Melanonus fusion of hypurals 1 and 2 is 

 both proximal and distal leaving a central opening 

 (Fig. 15A). Hypurals 3-5 although fused in specimens of M. 

 zugmayeri of 130mm SL are only partially fused in 66mm and 

 100mm SL specimens (Fig. 15B). Paulin (1983, fig. 5A) 

 figures a caudal skeleton of M. gracilis in which hypurals 1 

 and 2 are entirely fused and the fifth is reduced. In a 45mm 

 SL specimen of M. gracilis, all the hypurals are separated for 

 their entire lengths whereas in a 49mm SL specimen they are 

 fused distally but not proximally. There are two elongate 

 epurals each supporting a fin ray; in a 100mm SL specimen of 

 M. zugmayeri they are joined proximally (Fig. 15B). Unlike 

 morids, Melanonus lacks X and Y bones a feature shared with 

 Macruronidae, Gadidae and Lotidae. A long parhypural 

 articulates basally with the fused hypurals 1 and 2 and 

 supports a single fin ray. 



Comments on features of the vertebral column and median 

 fins. Chopstick-shaped ribs, similar to those of Melanonus, 

 have been reported for Macruronus, Lyconus, Steindachneria 

 and Merluccius by Okamura (1989) and Inada (1989) who 

 arrive at opposite conclusions with regard to their character 

 polarity. According to Okamura this rib-type suggests a close 

 relationship between the taxa in which they occur. Inada, on 

 the other hand, regards them as a plesiomorphic gadoid 

 feature. Although Inada's (1989) reasoning appear to be 



based on an a priori assumption of merlucciid plesiomorphy I 

 would agree with his assumption. In fact, this type of rib is 

 more widely distributed amongst gadoids than has been 

 reported and also occurs amongst 'supragadoids' other than 

 Merlucciidae (Fig. 14A). 



In Melanonus the ribs occur on vertebrae 3-5 as in Lyco- 

 nus, but they are on vertebrae 3 and 4 in Macruronus (both 

 Macruronidae), 3-6 in Merlucciidae, and 3-4 in Gaidrop- 

 saridae. In Steindachneriidae the ribs are on vertebrae 3 and 

 4 but the rib on the fourth has less than half the thickness of 

 that on the third whereas in the above cited taxa the ribs are 

 of equal thickness. Furthermore, the epipleurals attach 

 directly to the distal tips of the chopstick ribs in Steindachne- 

 ria whereas in the other taxa they are indirectly attached by 

 ligamentous strands running to the myosepta (as in Mel- 

 anonus). In morids and 'supragadoids' epipleurals are 

 attached directly to the vertebral ribs. Patterson & Rosen 

 (1989) interpreted the vertebral ribs Steindachneria and 

 Gadus as a parapophysis with attached epipleural. The ribs in 

 Steindachneriidae, however, are like those of Melanonidae, 

 Macruronidae and Merlucciidae in articulating with the ven- 

 tral cavity of the centrum. In the Bregmacerotidae the third 

 and subsequent vertebrae bear parapophyses to which are 

 attached cartilage-formed ribs (Fig. 14B). The loss of epi- 

 pleurals from the first and second centra is a gadiform 

 synapomorphy (Markle, 1989). 



Howes (1991b) regarded the first neural arch of Macruro- 



epr 



Fig. 14. Anterior region of vertebral column in: A, Gaidropsarus 

 mediterraneus; B, Bregmaceros sp. In A, black shading in the ribs 

 (ar) indicates zones of cartilage. 



