470 
PACIFIC SCIENCE, Vol. IX, October, 1955 
TABLE 3 
The Relationship between the Dorsal Origin and the Position of the Anus in Specimens 
of the Muraenichthys cookei-laticaudata Complex 
Distances are expressed in thousandths of the standard length. Plus values indicate distances of the dorsal origin 
in front of the anus; minus values, distances behind the anus 
SPECIES AND LOCALITY 
NUMBER OF 
DISTANCE FROM ANUS 
SPECIMENS 
Average 
Range 
Muraenichthys laticaudata 
Marshalls 
3 
—26 
—80 to + 11 
Muraenichthys cookei 
Hawaiian Islands 
Midway 
7 
12 
0 to + 23 
Oahu 
7 
20 
+ 3 to + 39 
Johnston 
12 
50 
+ 15 to +116 
ity is high and the available specimens from 
any one locality few. First, the two "species” 
cannot always be separated on the basis of 
the dorsal origin, for the ranges of the 
Marshallese and Midway specimens overlap. 
Second, the Marshallese M. laticaudata is most 
like the Midway form of M. cookei , which 
becomes progressively more distinct at Oahu 
and Johnston. One would like to know the 
nature of the populations of this species com- 
plex at Wake, a northern outlier of the Mar- 
shalls and somewhat between the rest of the 
group and Midway, but it has never been 
taken there. One would also like to know 
about the Line Island populations, but again 
the species complex is unrecorded from there. 
In the absence of evidence from these rather 
crucial localities, one can only speculate that 
the complex moved into Hawaii from the 
west, becoming further and further differ- 
entiated as it moved down the chain and 
thence to Johnston. Whatever the derivation, 
the fact remains that in the habitat (John- 
ston) that most resembles that of the pre- 
sumably ancestral M. laticaudata the differ- 
entiation is the greatest and in the habitat 
that least resembles the Central Pacific (Mid- 
way) the differentiation has been least. Thus 
the character by which M. cookei is disting- 
guished from M. laticaudata cannot be ex- 
plained as an adaptation to a cold-water 
environment; it would seem rather to be an 
instance in which differentiation has proceeded 
independently of the environment. 
Gymnothorax eurostus-huroensis 
The Hawaiian Gymnothorax eurostus is very 
similar to the Central Pacific species which 
has been called in recent years G. buroensis . 
Schultz (in Schultz, et ah , 1953: 120) has 
separated the two on the basis of minor color 
differences. The most important of these is 
the mottling of the lower jaw in G. eurostus 
as contrasted with the plain throat and lower 
jaw of G. buroensis. Unfortunately, G. eurostus 
at least is very variable in coloration, and 
almost any color character breaks down in 
some individuals. The color differentiation of 
the two species can, however, be supple- 
mented by a number of morphological char- 
acters, but for each of these there are, again, 
individual exceptions. At any given size over 
perhaps 7 inches, G. buroensis is a chunkier 
fish, and the head especially is higher and 
blunter, but both species become more heavy- 
bodied with age. (This and other proportional 
characters do not seem worth stating quanti- 
tatively because of the difficulty of obtaining 
reliable measurements on morays.) The 
mouth of G. buroenis closes completely; that 
of G. eurostus does not, leaving a gap between 
the lips just ahead of the eye when the jaw 
