36 
PACIFIC SCIENCE, Vol. XVIII, January 1964 
KEY TO THE PEARLFISHES OF GUAM 
A. Maxilla adnate to the suborbital Encheliophis B 
Maxilla not adnate to the suborbital; separated from it by a deep groove .. Carapus C 
B. Pectoral fins absent Encheliophis vermicularis 
Pectoral fins present Encheliophis gracilis 
C. Body everywhere covered with fine punctulations, each a single melanophore. These are 
in several layers and are present in the skin covering the eye. Pectoral fins reduced, 
almost vestigial, less than l A head length Carapus parvipinnis 
Melanophores not as above. Pectoral well-developed, more than *4 the head length D 
D. Body without superficial melanophores, although the meninges and peritoneum are pig- 
mented and there is a row of deep melanophores along the base of the anal fin and on 
the back of the skull, the nasal capsule, the lower and upper jaws. There are usually 
one or two conspicuous melanophores near the upper end of the ceratohyak ...Carapus homei 
Body with definite but sparse superficial melanophores in addition to those of the meninges 
and the peritoneum. Melanophores of the head not as above Carapus mourlani 
TABLE 1 
Distinguishing Characteristics of Four Species of Pearlfishes from Guam 
CHARACTER 
Encheliophis 
gracilis 
Carapus 
parvipinnis 
Carapus 
homei 
Carapus 
mourlani 
Maxillary bone 
adnate 
free 
free 
free 
Eye 
large 
tiny 
moderate 
moderate 
Pectoral fins 
large, j/3 head 
tiny, !4~ V$ head 
large, V2 head 
large, about Vi head 
Reverted lower lip 
absent 
present 
present 
present 
Gill membranes 
Gill opening extends 
broadly united 
slightly united 
slightly united 
slightly united 
above pectoral base 
no 
yes 
yes 
yes 
Body shape 
slightly compressed 
terete 
compressed 
compressed 
Superficial melanophores 
present, 1 layer 
present, several layers 
absent 
present, 1 layer 
Countershading 
Head pigment: 
present 
absent 
absent 
present 
cornea 
no 
yes 
no 
no 
nasal capsule 
no 
no 
yes 
no 
occiput 
not definite 
not definite 
definite 
not definite 
lower jaw 
yes 
yes 
no 
no 
ceratohyal 
absent 
absent 
present 
absent 
Teeth on jaws 
1 row 
2 series 
2 series 
2 series 
Host 
Holothurians 
Holothurians 
Holothurians 
Culcita 
It is of interest that only Carapus mourlani 
enjoyed an exclusive relationship with its host. 
All of the other three species occurred in two 
or more hosts. Perhaps this indicates that the 
utilization of a starfish as a host is a recent 
development and only this form has been able 
to make the necessary physiological adjustments. 
Other aspects of this relationship will be dis- 
cussed later. 
Stichopus chloronotus Brandt probably serves 
normally as host of only Carapus homei. The 
single specimen of Encheliophis found in this 
species could have come from a Holothuria 
argus Jaeger that had been placed in the same 
container with the Stichopus. There is no doubt, 
however, that H. argus serves as host to three 
species (E. gracilis, C. homei, and C. parvipin- 
nis ) since some of the collections contained only 
this host. 
Holothuria sp. (a stout-bodied, thread pro- 
ducing, burrowing form, whitish in color with 
two broad brownish transverse bands on the 
