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



MURAENOID LARVAE. 



37 



The pectoral fin is fan-shaped, with at least 10 rays, 

 and is situated directly above the posterior point of the jaw. 



The gill-opening is an oval slit situated directly in 

 front of the pectoral fin. 



The shape of the head and the development of the 

 jaws are shown in fig. 5 pi. VI. The eye is small, 06 mm 

 in diameter, and its anterior margin 

 is about 0-6 mm distant from the point 

 of the snout. 



I have only been able to discover 

 one nostril, which has the form of a 

 round pore and is placed directly in 

 front of the eye. Along the upper jaw 

 we find a row of organs greatly resemb- 

 ling the organs of the lateral line. 



In the jaw I have not been able 

 to discern any teeth. 



A brown fine-grained pigment 

 covers the entire animal, except for 

 the hindmost ventral portion of the 

 tail, which is transparent. 



In order to indicate the process of development from 

 the larval stage here described to the adult animal, I give 

 the following table, the figures for the young and adult 

 Gastrostotnus being taken from Zugmayer (38): — 



large specimens of Gastrostotnus have only 22. But as 

 this does not explain the decrease of the jaw, we are 

 compelled to accept that the tail-portion grows faster than 

 the head. 



The reverse must take place during the later growth 

 of the animal, when the head (with the jaws) grows 





Larva 



Young 

 Gastrost. 



Adult 

 Gastrost. 



Length of upper jaw in total length 

 Rostro-anal distance — „ — 

 Height near anus — „ — 



4.4 

 2-7 

 5-3 



5 



4 



36 



4-8 

 3-2 

 33 



This table reveals the peculiar circumstance that as 

 regards these three proportions of the body the young 

 Gastrostotnus occupies the most extreme position, the 

 upper jaw being comparatively the smallest, the anal 

 being situated nearest the front, and the height near the 

 anus being the smallest. It would seem therefore that 

 in the course of development the height of the animal 

 decreases rapidly, at the same time as the tail-portion 

 extends during the metamorphosis, which has begun in 

 our larva and is complete in the young Gastrostotnus, 

 consequently the jaw and the height become smaller, and 

 the rostro-anal distance decreases, in proportion to the 

 length. That this last mentioned relation is due to the 

 moving forwards of the anus seems to be evident, because 

 our larva has only some thirty preanal vertebrae, whereas 



Fig. 36. L. latissimus Schm. 

 (After Schmidt). 



proportionally most quickly, the height increasing some- 

 what at the same time. 



What was the course of development at earlier stages 

 than that of the larva in question? It seems unquestionable 

 that the earlier larva must have been a Leptocephalus, 

 for when we imagine the pigment gone, and the jaw- 

 portion less developed, we have before us a larva with 

 the characters of a Leptocephalus. It even seems to me as 

 if the larva in question in a way suggests what this 

 Leptocephalus must have looked like. 



In the first place the segments were probably compara- 

 tively perpendicular to the lateral line, the dorsal and 

 ventral angles lacking. Secondly the snout was quite 

 short, and the jaw probably inclined, with the eye situated 

 in front of the angle of the jaw. The height of the body 

 in our larva, though metamorphosis is in progress, is high, 

 and it may be supposed to have been still higher at an 

 earlier stage, probably decreasing rapidly towards the tail. 

 We must finally refer to a type of leptocephalids, of which 

 only one specimen is known, described by Schmidt (27) 

 first as L. latus, and later as L. latissimus. This form is 

 shown in fig. 36, and resembles our larva so closely that 

 I think it must be related to Gastrostotnus, but the number 

 of segments being so much greater than in Gastrostotnus 

 Bairdii, it is excluded that it can be the larva of that 

 species. 



