ATLANT. DEEP-SEA EXPED. 1910. VOL. III.). 



MURAENOID LARVAE. 



35 



The dorsal fin is inserted very far forward, whereas 

 the anal fin is inserted in the middle of the body, a 

 little nearer the anterior than the posterior extremity. 

 Both these fins are broad, having powerfully developed 

 rays, as have also the caudal fin (H l with six and H 2 

 with seven rays) and the pectoral fin, the latter placed 

 directly behind the gill-opening, and bearing about 14 

 rays. The gill-slits curve downwards towards the ventral 

 margin, and as far as I can see, they are confluent at 

 the front. 



The head is comparatively flat and broad, showing 

 distinct traces of advanced development. The snout is 

 rounded, and projects a little beyond the point of the 

 lower jaw. The anterior nostril is tubular, placed near 

 the point of the snout, and directed obliquely upwards, 

 while the posterior nostril is a small round pore just in 

 front of the eye. The eye exceeds 1 mm in diameter, 

 and is placed far in front of the angle of the jaws. The 

 jaws retain a few rather small, apparently larval teeth. 

 Series of mucous pores run along the jaws. 



I have not been able to determine exactly the number 

 of muscle-segments, but approximately there are 50 preanal 

 and 77 postanal segments, 127 in all. Although this 

 figure agrees with the number of segments in L. Michael- 

 Sarsi, there can hardly be any doubt that the two forms 

 are distinct, for they differ in the number of rays in the 

 caudal and anal fins, and the tubular nostril in this larva 

 is directed obliquely upwards, while in L. Michael-Sarsi 

 it is directed obliquely downwards. 



I cannot refer this extraordinary larva to any known 

 species of Leptocephali, and have been unable to identify 

 it with any adult form, and have therefore described it 

 as distinct. 



26. Leptocephalus Gastrostomi Bairdii. 



A larva undergoing transformation, perhaps the most 

 peculiar in the collection, was taken at Stat. 64 in the 

 net at 1000 metres. Whereas the trunk has retained very 

 many of its larval characters, from which a conclusion 

 as to its previous leptocephalid appearance may be drawn, 

 the head, especially the maxillary portion, has undergone 

 a development plainly proving the animal to be the larva 

 of a fish belonging either to Eurypharynx or Gaslrostotnus 

 or some allied form. 



Before endeavouring to determine to what species 

 this peculiar larva belongs, we must give an account of 

 those species with which it may be compared, viz: — 



1) Enryphatynx pelecan0ld.es Vaillant; 2) Gastrosto- 

 my Bairdii Gill and Ryder; 3) Maciopharynx longlcau- 

 datus Brauer; 4) An undescribed form taken by the 



"Michael Sars" in 1910, which for convenience we may 

 call "species A". 



There is also the possibility that it may be the larva 

 of some closely allied form hitherto undescribed. 



The single specimen of Maciopharynx longicaudatus 

 described by Brauer is according to Zugmayer (38) who 

 had more abundant material for investigation, merely a 

 young individual of Gastrostomus Bairdii. 



Vaillant (37) says that in Eurypharynx pelecanoides, 

 of which, as far as I have been able to ascertain, only 

 three specimens are known, "la peau est absolument nue, 

 sans ligne laterale distincte". Species A is also distin- 

 guished by the absence of a distinct lateral line. 



Gastrostomus Bairdii, however, has a lateral line, 

 strongly marked by peculiar organs. I have had an 

 opportunity of examining a number of specimens of this 

 species, and the lateral line could be seen very distinctly 

 with the naked eye in the small specimens as well as in 

 the larger ones. 



The larva in question has a very distinct lateral line, 

 and indeed has so many specific characters in common 

 with Gastrostomus Bardii, that I have little hesitation in 

 referring it to that species. 



Beginning with the organs of the lateral line, we 

 find the structure and arrangement strikingly like those 

 in Gastrostomus Bairdii, but apparently the organs are 

 less fully developed. These organs are not accurately 

 shown in the published drawings of Gastrostomus Bairdii, 

 so I re-examined eight specimens of this species, and 

 found two types of organs in every specimen. One type 

 consists of a row of three or four light-coloured oval 

 spots, placed obliquely, sometimes inclined to the right, 

 sometimes to the left. The second type consists of a 

 single light-coloured spot placed between two of the 

 oblique rows, as indicated by Brauer (2) in his drawing 

 of Macropharynx longicaudatus. 



We find the first type of organs distinctly developed 

 in our larva, the 3 or 4 elements being, however, not 

 oval, but subcircular or subangular. There are also in a 

 few places unmistakable indications of organs of the 

 second type between those of the first type. Thus in 

 regard to the organs of the lateral line this larva corre- 

 sponds closely with Gastrostomus Bairdii, and is by 

 this feature distinguished from Eurypharynx pelecanoides 

 and species A. 



In other respects we also find a remarkable agree- 

 ment. Zugmayer (38) investigated the vertebral column 

 in Gastrostomus Bairdii, and discovered a peculiar feature 

 about the fifth and the sixth vertebra, which he thus 

 describes: — "Les vertebres sont regulieres a l'exception 

 de la cinquieme et de la sixieme, qui sont plus basses que 

 les autres et qui en se rencontrant forment un angle dont 



