Pacific Plate Biogeography, with Special Reference to Shorefishes

NUMBER 367
the Plate only from the Hawaiian Islands, but
J.E. Randall informs me he sighted a specimen
in the Line Islands in 1968. The species can
probably be considered as an Hawaiian exception
with occasional waifs appearing elsewhere on the
Pacific Plate. Two species, A. achilles and A. leucopareius
(Figure 5), should possibly be considered
as widely distributed Pacific Plate endemics that
have undergone a relatively recent westward dispersal
which has enabled them to reach the western
margin of the Philippine Plate (see section on
geology of Pacific and Philippine plates). Acanthurus
achilles is known nonmarginally off the Pacific
Plate only from Cebu, Philippines (Rau and Rau,
1980), where it and A. leucopareius appear uncommonly
in the fish market (N. Rau, in litt.). The
distribution of A. leucopareius is also noteworthy
because of its disjunct, antiequatorial nature
(Randall's 1976 report of A. leucopareius from Lord
Howe Island was in error; Marcus Island—on the
Pacific Plate—was the intended locality; Randall,
in litt.).
Acanthurus nigroris also appears to be a widely
distributed Pacific Plate endemic, although Randall
(in litt.) suggests that it may occur west of
the Plate as a straggler (see Whitley, 1958, for a
record from the Great Barrier Reef). There is one
other Pacific Plate endemic species of Acanthurus,
A. chronixis, known only from Kapingamarangi,
Eastern Caroline Islands (Randall, 1960, and
pers. comm.; misidentified from New Guinea by
Burgess and Axelrod, 1975, fig. 418 = A. pyroferus).
The intrageneric relationships of the Plate endemic
species of Acanthurus are unknown.
Ctenochaetus comprises six species (Randall,
1955c, 1960) and ranges throughout the Indo-
Pacific, one species also reaching the eastern Pacific.
At least five of the species occur on the
Pacific Plate nonmarginally, and one, C. hawaiiensis,
is a widely distributed Pacific Plate endemic,
known from the Mariana, Marcus, Marshall, Hawaiian,
Line, Austral, Society, Samoa, Tuamotu,
and Pitcairn Group islands.
Naso (including Axinurus and Callicanthus) contains
about 16 species (Srm'th, 1966a; Randall
and Struhsaker, 1981; J.E. Randall, in litt.), of
which at least nine extend onto the Pacific Plate
nonmarginally (eight ranging from the east coast
of Africa, and one restricted to Japan and the
Hawaiian Islands). The other seven species are
restricted to various parts of the Indo-West Pacific,
and some are of questionable validity.
Prionurus (including Xesurus) has six species, of
which two are limited to the eastern Pacific, one
to the eastern Atlantic, and three to the western
Pacific (Smith, 1966a). Prionurus is the only acanthurid
genus that is absent from the nonmarginal
portions of the Pacific Plate.
Paracanthurus is monotypic (Randall, 1955b)
and ranges throughout the Indo-Pacific, from the
east coast of Africa to at least the Line Islands
(Chave and Eckert, 1974), but it is absent from
the Hawaiian Islands.
Zebrasoma contains seven species. Randall
(1955b) recognized six species, but now (in litt.)
recognizes a seventh, Z. desjardinii, for the Indian
Ocean populations of the species he treated as Z.
veliferum from the Indo-Pacific. Two other species
(Z gemmatum, Z. xanthurum) are restricted to the
Indian Ocean, and one species (Z. scopas) ranges
from the western Indian Ocean to the Society
Islands. Zebrasoma rostratus is a Pacific Plate endemic
known positively only from the Tuamotu,
Marquesas, Line, and Rapa islands. Zebrasoma
Jlavescens should possibly be considered a Plate
endemic; it has been reported from Taiwan and
the Ryukyu Islands, along the western margin of
the Philippine Plate, where it appears to be uncommon,
east to the Bonin, Mariana, Marshall,
Wake, Marcus, Hawaiian, and Johnston islands.
In summary, there are five genera and 64 Indo-
Pacific species of acanthurids, of which 39 species
occur on the Pacific Plate nonmarginally, and
possibly seven of these 39 are Plate endemics.
ALBULIDAE
The bonefishes comprise two genera (Forey,
1973): Pterothrissus (sometimes placed in its own
family, Pterothrissidae) with two, moderately
deepwater species (one known from off Japan, the
other from off west Africa), and Albula, with
perhaps as many as six species, several of which
have been confused with one of the two currently
11