PROCEEDINGS OF THE CALIFORNIA ACADEMY OF SCIENCES I Volume 51, No. 14, pp. 473-481, 6 tigs., 1 table. December 9, 1999 DEC 2 1999 Acanthiiriis reversiis^ a New Species of Surgeonfish (Perciformes: Acanthuridae) from the Marquesas Islands by John E. Randall and John L. Earle Bishop Museum, 1525 Bernice St., Honolulu. Hawaii 96S 1 7-2704 Acanthunis reversus is described as a new acanthurid fish from five specimens from the Marquesas Islands. It is most similar to Acanthurus oUvaceus of the central and western Pacific, differing principally in color. The caudal fin is pale yellow instead of gray-brown with small dark spots, and it has a black crescent posteriorly instead of a dark-edged white crescent; there is a broad, deep blue, longitudinal band in the humeral region with an elongate orange spot centered anteriorly, not reaching more than halfway back within the deep blue band (in A. oUvaceus orange band is broader and extends nearly to the end of the blue band). Like A. oUvaceus the young are bright yellow. Acanthurus reversus also differs in having longer dorsal spines (longest spine 15.2-16.3% SL, compared to 12.0-14.5% in A. oUvaceus and the caudal spine is shorter on the average (7.7—10.8% SL, compared to 9.8—1 1.5% in A. oUvaceus). While snorkeling in Takaroa Atoll in the northern Tuamotu Islands in November 1956 one of us (J. E. R.) speared a surgeonfish, 175 mm standard length (measured fresh). It was much like the wide-ranging .4(:(7/?//?//r//,v oUvaceus. but there was only a small elongate orange spot anteriorly within the broad, deep blue band of the shoulder region, and the color of the caudal fin was very different, pale yellow without dark spots, and with a black crescent posteriorly in the fin instead of a white one. Typical A. oUvaceus was common at the atoll, and the odd-colored fish was swimming with several individuals of this species. Four of the A. oUvaceus specimens were speared from the area and compared with the atypical specimen. No morphological differences were found, but two of the four specimens of A. oUvaceus had a narrower humeral orange band that was diffuse posteriorly; their caudal coloration, however, was typical of.^. oUvaceus. Due to limited formalin, only the odd-colored specimen was preserved. It was deposited in the U. S. National Museum of Natural History as USNM 1 698 1 ; the standard length is now 1 68 mm. In July, 1957 J. E. R. sailed his 10-m ketch Nani from Tahiti through the Marquesas Islands. There he found the odd-colored surgeonfish to be abundant, but no typical A. oUvaceus were observed. One specimen of the Marquesas Is. form, 196 mm SL, was speared at Anaho Bay, Nuku Hiva and deposited in the Stanford Natural History Museum. Unfortunately, this specimen could not be found in the collection of the California Academy of Sciences where the Stanford University fish collection is now housed. It was concluded that the one fish at Takaroa was a Marquesan form that was transported as a larva from the Marquesas Is. in the prevailing current. Randall ( 1 960) discussed the Marquesan variant and indicated that it should be regarded as a subspecies of .4. oUvaceus. He declined to name it and indicated that additional specimens should be procured from both the Marquesas Is. and Tuamotu Archipelago. 473
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