Munroe: Systematics of western Atlantic Symphurus 
149 
of Paraplagusia are known (Chapleau and Renaud, 
1993). Symphurus is also the most diverse pleuro- 
nectiform taxon occurring in the western Atlantic 
ocean. The other speciose pleuronectiform genera in 
this region, the paralichthyids Citharichthys (with 
ca. seven species) and Paralichthys (ca. 11 nominal 
species), are both distinctly less speciose than the 24 
species of symphurine tonguefishes. 
The Symphurus species assemblage in the west- 
ern Atlantic is diverse both in terms of numbers of 
species and in diversity of species groups. Five of nine 
species groups recognized in the genus (Munroe, 
1992 ) have species in this region. Unique to the west- 
ern Atlantic, is a group of four species with the 1-4-2 
ID pattern. The majority (9/11) of species possessing 
a 1-4-3 ID pattern are found in the western Atlantic, 
with two others occurring in the eastern Pacific. Nine 
western Atlantic species have a 1-3-2 ID pattern. 
Seven other species, four in the eastern Pacific and 
three in the eastern Atlantic, share this ID pattern. 
Only S. trewavasae among western Atlantic tongue- 
fishes has the 1-3-3 ID pattern, but three other spe- 
cies, one eastern Atlantic and two eastern Pacific, 
share this ID pattern. Symphurus nebulosus is also 
unusual in that it is the only western Atlantic spe- 
cies characterized by a 1-2-2 ID pattern. At least 14 
other species in the genus possess this ID pattern, 
and all, except the eastern Atlantic S. ligulatus, are 
found in the Indo-Pacific. No western Atlantic 
tonguefishes have the 1-2-2-1-2 ID pattern limited 
to one eastern Atlantic and six Indo-Pacific species, 
the 1-2-3 pattern of three nominal Indo-Pacific spe- 
cies, the 1-3-4 limited to one eastern Pacific species, 
or the 1-5-3 ID pattern found in eight eastern Pa- 
cific species. 
The diversity of symphurine tonguefish species 
recorded from the western Atlantic is comparable 
with that of the Indo-Pacific (ca. nominal 24 species), 
and is greater than the 17 found throughout the east- 
ern Pacific region (Munroe, 1992; Munroe et al., 
1995). There are four times as many species of 
Symphurus in the western Atlantic as in the com- 
paratively depauperate eastern and central Atlantic 
regions combined, where only six species are known 
to occur (Munroe, 1990). 
The greater diversity of symphurine flatfishes in 
the western compared with the eastern Atlantic re- 
flects not only differences in composition of the spe- 
cies groups between these areas but also the greater 
diversity of habitats available to, and occupied by, 
tonguefishes in the western Atlantic. Members from 
two species groups (four species with 1-4-2 ID pat- 
tern and seven with 1-4-3 ID pattern) are especially 
abundant in shallow-water and neritic habitats of 
the western Atlantic but are entirely absent in the 
eastern Atlantic. Also, more western Atlantic species 
(n= 8) with the 1-3-2 ID pattern are known than are 
found in eastern and central Atlantic areas (where 
only three species have this ID pattern). Other east- 
ern Atlantic Symphurus are a single species each 
with either a 1-2-2, 1-2-2-1-2, or a 1-3-3 ID pattern, 
and members of these species groups typically in- 
habit substrates on the continental shelf and upper 
continental slope (Munroe, 1992). The few shallow- 
water representatives in these groups are found on 
sandy substrates in coral reef environments. The 
eastern Atlantic region lacks the diversity of sub- 
strates found in tropical and subtropical regions of 
the western Atlantic, largely as a consequence of the 
comparatively narrow continental shelf off tropical 
West Africa with its highly turbid, cool waters and 
lack of extensive coral reefs and associated habitats. 
The more diverse symphurine tonguefish fauna in 
the western Atlantic results from the presence of 
species groups (i.e. those with 1-3-2, 1-4-3, and 1-4-2 
ID patterns) that successfully exploit relatively shal- 
low-water habitats, including the extensive coral 
reefs and associated habitats, which are more com- 
mon on the comparatively wide continental shelves 
in the western Atlantic. 
Large differences in diversity occur in other dis- 
tantly related fish groups occurring in both eastern 
and western regions of the Atlantic Ocean (Briggs, 
1974; Collette 9 ). Among these are toadfishes (Batra- 
choides ), which are closely associated with the sub- 
strate, as well as fishes lacking strong substrate af- 
finities, including needlefishes ( Strongylura ), 
halfbeaks ( Hyporhamphus ), and Spanish mackerels 
(Scomberomorus). Greater species diversity within 
these genera in western Atlantic regions, irrespec- 
tive of degree of substrate association for the compo- 
nent taxa, indicates that factors other than substrate 
diversity account for the greater number of species 
found in the western Atlantic. 
None of 24 western Atlantic species of Symphurus 
are known to occur in the Indo-Pacific, eastern Atlan- 
tic, or eastern Pacific regions. However, several hypoth- 
esized species pairs are identified among western At- 
lantic species, and among western Atlantic species and 
those from eastern Atlantic or eastern Pacific regions. 
Hypothesized species pairs occurring in northern ( listed 
first) and southern regions of the western Atlantic are 
S. billykrietei : S. ginsburgi; S. parvus : S. kyarop- 
terygium ; and S. civitatium: S. plagusia. 
Symphurus billykrietei and S. ginsburgi represent 
a species pair with distinct antitropical distribution. 
9 Collette, B. B. 1997. National Marine Fisheries Service Sys- 
tematics Laboratory, National Museum of Natural History, 
Washington, D.C. 20560. Personal commun. 
