ATI.ANT. DEEP-SEA EXPED. 1910. VOL. III]. 



MURAENOID LARVAE. 



15 



widely distributed over the portion of the North Atlantic 

 investigated. 



It seems reasonable therefore to assume: — Firstly, 

 that as there are two groups differing greatly in devel- 

 opment, in one case taken at the same place, these groups 

 must be annual series, and that consequently it takes a 

 year at least from the time the larva leaves the egg until 

 it reaches its full larval development; secondly, that the small 

 "prelarvae" lives nearer the surface than full-grown larvae. 



The great distances between the finding-places for 

 the smaller larvae apparently support the assumption, that 

 the spawning-area of this species is very large. 



3. Leptocephalus Histiobranchi infernalis 

 for L. llyophidis Brunnei). 



A larva taken at Stat. 62 in the net at 100 m reminds 

 us very much of Leptocephalus Synaphobranchi pinnati, 

 but that form has more than 140 segments, while this larva 

 has only 133 or 134 segments (see fig. 10 and pi. II). Its 

 great resemblance to the larva of Synaphobranchus led 

 me to conclude that it must be the larva of a nearly 

 related species, probably Histiobranchus infernalis, and 

 the first examination of an adult Histiobranchus seemed 

 to confirm this, for I found 132 vertebrae, rays in the 

 pectoral and caudal fins agreed in number, and the hypural 

 bones had the same shape. I therefore took it for granted 

 that the larva was Leptocephalus Histiobranchi infernalis. 

 But when I examined a young specimen, which my colleague 

 mag. sc. E. Koefoed and myself independently determined 

 as Ilyophis Brunneus, 1 ) I found that it also had the very 

 same number of vertebrae, the same number of rays in 

 the pectoral and caudal fins, the same shape of hypural, 

 and even some small lateral processes on the bases of 

 the caudal rays found in Histiobranchus and in our larva. 



Comparing this larva with the specimens of Histio- 

 branchus and Ilyophis examined by me, the close agree- 

 ment as regards the number of segments and the number 

 of rays in the pectoral and caudal fins, is shown in the 

 following table : — 



Number of muscle-segments (verte- 

 brae) 



Number of rays in the pectoral fin 



Number of rays in the caudal / H : 



fin \H„ 



Larva 



133-134 

 15—16 



Histio- 

 branchus 

 infernalis 



132 



15-16 

 8 



Ilyophis 

 Brun- 

 neus 



132 

 1-1 



Further it may be mentioned that the young specimen 

 of Ilyophis and a young specimen of Histiobranchus are 

 furnished with the processes at the bases of the caudal 

 rays already mentioned. They are also found in our larva 

 in a less marked form, whereas 1 was not able to discover 

 them in a large specimen of Histiobranchus. 



Accordingly I cannot refer our larva to either of these 

 species with certainty, but must leave the question open 

 for the present. It may be that Ilyophis is not distinct 

 from Histiobranchus; the former has been described from 

 a single specimen, while the latter has not been described 

 in great detail, and the possibility of sexual dimorphism, 

 for instance, is not to be disregarded. 



Our larva gave the following measurements: 



Length 87 mm 



Anus 67 „ 



Dorsal 61 



Height 8 „ 



Head 6-8 „ 



Snout 2-5 „ 



The musculature of the body resembles greatly the 

 musculature in L. Synaphobranchi pinnati. The segments 



Fig. 10. Head of larval Histiobranchus infernalis 

 or Ilyophis Brunnei. l %. 



are curved without the usual dorsal and ventral angles. 

 As preserved the musculature along the lateral line is 

 opaque, while being rather transparent dorsally and ven- 

 trally, and this gives rise to the whitish lateral streak. There 

 are 93 preanal, and 41 postanal segments. The alimentary 

 canal has no striking peculiarities. Rays are developed 

 in all the fins. The caudal fin is like that of L. Syna- 

 phobranchi pinnati, with the posterior margin of H 2 forming 

 an angle of about 45° with the longitudinal axis of the 

 animal. The pectoral fin has the form of a small fan. 

 Pigment is present only on the caudal fin, as scattered 

 dots too small to be seen with the naked eye. 



') The specimen in question has well-separated gill-openings, and the branchiostegal rays are longer and more curved than in a 

 specimen of Histiobranchus of equal size. 



