272 
Fig. 4. Juvenile of Acanthurus leucosternon Bennett 
from the Maidive Islands; standard length 54 mm. 
Dark area around pectoral fin is shadow. Photo by W. 
Courtenay. 
Ocean, and A. glaucopareius , also a near relative, 
is known in the Indian Ocean only from Cocos- 
Keeling and Christmas islands. 
The juvenile stage of A. leucosternon (Fig. 
4) is very similar to the adult. The acronurus, 
unless it is the Acronurus formosus of Castelnau 
(Randall 1936b: 202), has not been described. 
It may be large like the acronuri of A. achilles 
and A. glaucopareius . 
Marden (1956: 185) has portrayed Acanthu- 
rus leucosternon in an underwater color pho- 
tograph. The body of the fish is bright blue. A 
broad blackish band curves down from the in- 
terorbital region, enclosing eye, and covering 
most of the operculum. The dorsal fin is bright 
yellow edged with blue, and the caudal peduncle 
and region of caudal spine are also yellow. The 
caudal fin is black with a large crescent of white 
and a blue margin posteriorly. The anal and 
pelvic fins are white, and there is a white area 
on the chest and a white band on the chin. 
Dorsal and anal fin-ray counts of A. lineatus 
from the Indian Ocean and the Pacific (Table 
3 ) suggest differentiation of the species in these 
two oceans. A. lineatus is known from the coast 
of East Africa, but not from the Red Sea where 
a similar but very distinctive species, A. sohal, 
appears to be endemic. 
The dorsal soft rays of three specimens of 
Zebrasoma veliferum from the Maldives number 
27-30, and the anal soft rays 22-24. These 
counts align themselves with those from other 
Indian Ocean localities which differ significantly 
from counts of specimens from the Pacific 
(Randall 1955c: table 1). 
Dorsal soft rays of 10 specimens of Acanthu- 
PACIFIC SCIENCE, Vol. XIV, July I960 
rus tennenti collected by Morrow in the Sey- 
chelles number 22-24 (mostly 23), and the anal 
soft rays 21-23 (mostly 22). 
Smith (1955: 692) listed the acanthurids 
from the island of Aldabra in the Indian Ocean 
north of Madagascar and described two of them 
as new. One, Acanthurus bicommatus (pi. 
XVIII, C and D in Smith), is a synonym of 
A. tennenti. The second, A. melanosternon (pi 
XVIII, B), is a valid species, differing from 
others principally in the nearly black color of 
the chest which encloses a broad white patch 
below the middle of the lower preopercular mar- 
gin, this patch in some specimens continuing 
as a band midventrally, thus dividing the black 
area anteroposteriorly. This white band on the 
chest is suggestive of A. leucocheilus Herre from 
the Philippines, as is the outer pale one-third 
of an otherwise dark pectoral fin. A. melan- 
osternon lacks the bluish-white band at the base 
of the caudal fin, the black snout with a white 
band encircling the mouth, and the dark red 
lines distally in the dorsal and anal fins of 
leucocheilus. Meristic data were given by Smith 
as follows: D IX, 25-26; A III, 24-25; P 17; 
gill rakers 21-22. He had numerous specimens, 
280-480 mm. in length, taken over a wide area 
of East African coast as far south as 15° and 
at various islands in the Indian Ocean. 
Also listed by Smith among the species of 
Acanthurus from Aldabra and East Africa is A. 
philippinus Herre (= A. thompsoni (Fowler)). 
This represents the first record of A. thompsoni 
from the Indian Ocean. 
Three species of Ctenochaetus were recorded 
TABLE 3 
Fin-ray Counts of Specimens of 
Acanthurus lineatus FROM INDO-PACIFIC LOCALITIES 
LOCALITY 
DORSAL SOFT RAYS 
25 26 27 28 29 30 
ANAL SOFT RAYS 
25 26 27 28 
Maidive Is. 
118 2 
15 5 1 
Seychelle Is. 
2 2 
1 2 1 
Mauritius 
1 
1 
Palau Is. 
1 4 2 
6 1 
Mariana Is. 
5 9 3 
1 10 6 
Samoa Is. 
5 2 1 
2 5 1 
Society Is. 
4 4 
3 5 
Marquesas 
Is. 
1 
1 
