A canthurus— Randall 
277 
Fig. 7. Naso rigoletto Smith from Tahiti; standard 
length 565 mm. Reproduced from a 35 mm. Koda- 
chrome transparency. 
head (according to Smith, only the males of 
this species possess a long rostral prominence). 
This fish was gray on the dorsal half of the body 
and light gray ventrally. There were about five 
small blue spots anteriorly on the body above 
the pectoral fin and two such spots posteriorly 
on the head. The caudal spines were not colored. 
Fin-ray counts are as follows: D V, 30; A II, 
29; P 17. 
N. rigoletto was sighted underwater at Eiao, 
Marquesas, as was N. lituratus ( Bloch and 
Schneider ) , but was not taken. 
The surgeonfishes previously known from the 
Marquesas Islands include Ctenochaetus cyano- 
guttatus, Acanthurus lineatus, A. triostegus, and 
A. glaucopareius ; all of these are common. The 
acanthurids which represent new additions to 
the Marquesan fauna are A. pyro ferns, A. oliva- 
ceus, Ctenochaetus strigosus, Zebrasoma rostra- 
tum, A. achilles, A. guttatus Bloch and Schneider, 
A. nigroris Cuvier and Valenciennes, A . xan- 
thopterus Cuvier and Valenciennes (a 474 mm. 
specimen; only the head preserved), A. blee- 
keri Gunther, and Naso unicornis (Forskal). 
The specimen of Acanthurus bleekeri is 280 
mm. in standard length. It was one of a school 
of about 30 fish at Eiao which varied in hue 
from pale bluish to dark brown. The broad yel- 
low band through the eye was conspicuous re- 
gardless of ground color. 
The specimen of Naso unicornis measured 
448 mm. in standard length; it possessed a 
horn which extended directly forward from the 
eye. The lower edge of the horn measured 52 
mm. from the head. Counts of the specimen 
were as follows: D VI, 30; A III, 29; P 18. The 
color in life was gray on the back shading to 
yellow ventrally, with a patch of blue blotches 
in the region of the pectoral fin; the dorsal and 
anal fins were alternately striped with diagonal 
bands of orange and blue; the caudal fin was 
gray, becoming yellowish outwardly. Only the 
caudal region and snout were preserved. 
Most of the acanthurids from the Marquesas 
Islands have been deposited in the SNHM. 
Although only 12 days were spent in collect- 
ing and observing fishes in the Marquesas, it 
seems likely that certain surgeonfishes such as 
Ctenochaetus striatus, Acanthurus nigrofuscus, 
and A. gahhm, common throughout the South 
Seas, are absent in this island group. Little ob- 
servation is needed to notice that the Marquesas 
have an impoverished fish fauna. This is more 
evident for many other families of fishes, such 
as the Labridae and the Chaetodontidae, than 
it is for the acanthurids. The explanation for the 
scant fauna probably lies both in the eastern 
position of the Marquesas in the Indo-Pacific 
in a region of westward-moving current and 
in the paucity of coral reefs. 
SUMMARY 
1. Acanthurus chronixis is described as new 
from Kapingamarangi Atoll, Caroline Islands. 
The description is based on a single 211 mm. 
specimen. Two juveniles from Ifaluk in the 
Carolines, probably belonging to this species, 
are described in detail. Due to slight meristic 
differences from the holotype, these small spec- 
imens are not designated as paratypes. 
A. chronixis is one of three known species of 
Acanthurus with eight dorsal spines. It appears 
to be closely related to A. pyroferus, sharing 
with it the dorsal-spine count, a somewhat 
produced snout, and a spherical, thick -walled 
stomach. It differs from A. pyroferus primarily 
in color pattern. 
2. The juvenile stage of Acanthurus pyroferus 
is bright yellow in life with blue and orange 
markings and a rounded caudal fin. It closely 
resembles the angelfish Centropyge flavissimus, 
thus suggesting mimicry. 
3. The population of Acanthurus pyroferus in 
the Society Islands appears differentiated from 
populations in the Marshall Islands and Philip- 
pines on the basis of a higher number of soft 
rays in the dorsal and anal fins. 
