STRUCTURE AND SYSTEMATICS 55 



Neoscopelus 



Apart from the uncertainty of its type of swimbladder, this genus is readily distinguished from all 

 myctophids in the number of retia mirabilia, there being more than three retia (five in two individuals 

 that were examined (Text-fig. 30 d). Neoscopelus has been classified within the Myctophidae, either 

 as one of the genera, or as the type, of the subfamily Neoscopelinae (Fraser-Brunner, 1949). In many 

 ways it is quite unlike the myctophids (sensu stricto), particularly in the arrangement and structure of 

 the light organs (Brauer, 1908). Such differences, together with those found in the swimbladder, 

 certainly indicate that the genus should be placed apart from the myctophids. As already suggested 

 (Marshall, 1955), it might be better to put it into a separate family (Neoscopelidae) together with the 

 genera Scopelengys and Solivomer. 



Order Miripinnati 



The basic features of the swimbladder of these fishes have already been described (Bertelsen and 

 Marshall, 1956). In the sharp separation of an anterior thick-walled secreting part from a posterior 

 thin-walled resorbent part, the organ is euphysoclistous, but there appears to be no diaphragm. The 

 gas-gland receives its blood supply through two unipolar retia mirabilia that originate in the middle 

 region of the sac and are formed from a posterior artery and vein (Text-fig. 30 e). 



The only known oceanic fishes with two such retia mirabilia are Anoplogaster and Stephanoberyx, 

 but in the latter genus, and in the Melamphaidae, the resorbent part of the swimbladder is formed by 

 an oval. 



Order AUotriognathi , Family Stylophoridae 



The swimbladder of Stylophorus is readily distinguished from those of other pelagic, deep-sea fishes. 

 It is euphysoclistous with a single unipolar rete mirabile receiving blood from an artery-vein pair 

 that originates in front of the forward end of the sac. Unlike most euphysoclists, the front half of the 

 swimbladder is provided with a resorbent capillary system, while the rear half contains the gas- 

 producing glandular tissue (Text-fig. 30F). The organ regresses during adult life. 



Order Berycomorphi 



The bathypelagic members of this group are mainly to be found in Regan's ( 1 9 1 1 ) order Xenoberyces. 

 The families are Stephanoberycidae, 1 Anoplogastridae and Melamphaidae. Parr (1929) also placed 

 the Rondeletiidae in Regan's order, but Harry (1952) has provided ample evidence for regarding this 

 family, together with the Barbourisiidae and Cetomimidae, as forming a 'natural group widely 

 distinct from all other families of fishes. . .'. The three genera considered in this report, Stephano- 

 beryx, Anoplogaster and Melamphaes, all have a closed swimbladder 2 with one or two unipolar retia 

 mirabilia that originate at the posterior end of the sac. 3 In Stephanoberyx and Melamphaes, the swim- 

 bladder is definitely euphysoclistous, for an 'oval' is present (Text-fig. 30 G, h). 



Regan (191 1) decided that the Stephanoberycidae and Melamphaidae were sufficiently different 

 from ' typical Berycomorphi ' to be placed in a separate order, Xenoberces. They are also distinct in 

 swimbladder characters. As we have seen, in Stephanoberyx, Anoplogaster and Melamphaes, there are 

 one or two retia that originate at the posterior end of the swimbladder. In the Berycomorphi, as 

 restricted by Regan, all available evidence shows that the retia originate at the anterior end of the sac 

 (Rauther, 1922; Nelson, 1955). 



1 Stephanoberyx may be demersal rather than pelagic in habit. 

 Stephanoberyx is said to have a pneumatic duct (Regan, 191 1 ; Berg, 1940), but I was unable to find one. 

 Dr A. Ebeling, who is revising the Melamphaidae, has been good enough to tell me that in certain melamphaids 

 (Melamphaes s.s.) the retia are at the front of the swimbladder. 



