304 
PACIFIC SCIENCE, VoL V, October, 1951 
rp rb 
Fig. 10. a. Tail of Muraenichthys {Muraemchthys) 
cookei; b, of Cirrhimuraena macgregori. im, Intermus- 
cular bone; rb, basal segment of fin ray; rp, peripheral 
segment of fin ray. 
DIAGNOSIS AND RELATIONSHIPS 
Compared with other eel families the most 
diagnostic features of the Ophichthidae ap- 
pear to be as follows: 
Dorsal and anal rays either reduced or 
absent at tip of tail. Posterior nostril be- 
low the level of the eye, either on the 
inside or the outside of the upper lip. 
Skull not truncate behind. Frontals fused 
to form a single bone. Suspensorium 
nearly or quite vertical. Auditory bullae 
present. Branchiostegal rays of the two 
sides of the head broadly overlapping on 
the mid- ventral line. Neural spines rudi- 
mentary. Intermuscular bones well de- 
veloped. Strong transverse processes on 
caudal vertebrae. 
Since the appearance of Regan’s excellent 
paper on eel classification (1912), it has been 
generally agreed that the Ophichthidae are a 
specialized offshoot of the cpngrid stock. : 
Nevertheless, it is necessary here to compare ; 
the ophichthids and congrids, partly because 
no adequate comparison of the two groups 
exists, and partly to indicate the nature of the 
specializations in the Ophichthidae. 1 
The ophichthids differ immediately in two || 
superficial characters— the labial nostril and ij 
the reduced or absent tail fin. However, these | 
characters are not as significant as they might | 
appear to be. 
In the Congridae the posterior nostril opens 
out in the cheek in front of the eye. A pos- j 
terolateral deflection of this opening would ij 
place it where it occurs in the ophichthid ;| 
Caecula flavicauda (Fig. 14^) . In those ophich- I 
thids that have the narial opening inside the ji 
upper lip, the posterior nostril is carried down |i 
in a tube (outside the infraorbital canal, as 
pointed out by Allis [1903]) over the surface 
of the upper lip and into the mouth. Often i 
the groove behind this tube is still visible i 
externally, as in Myrichthys (Fig. 15), but i 
sometimes the tube has been completely fused |l 
into the lip. This same specilization of an 
internal posterior nostril occurs in the un- j 
related family provisionally called Echelidae : 
(Gosline, 1950). 
The reduction or loss of fin rays at the tip 
of the tail is probably an adaptation to dig- 
ging, as pointed out by Myers and Storey 
(1939: 157). That such loss is secondary is 
shown by the presence of reduced fin rays 
around the tail of Myrophinae (Fig. 10^^) and 
the fin rudiments that remain in certain 
Ophich thinae (Fig. 10^). 
Osteologically, Conger (Fig. 11) shows ! 
numerous characters in which it is undoubted- ii 
ly more primitive than the Ophichthidae. In i 
most of these it resembles the Anguillidae. 
However, the Congridae and the Anguillidae 
differ at once in that the frontals of the 
Anguillidae are separate, whereas those of the 
Congridae are fused into a single bone. Pri- 
