Munroe: Systematics of western Atlantic Symphurus 
151 
summarized herein indicate that for the majority of 
western Atlantic species, the center of abundance of 
the adult population is usually concentrated within 
a relatively narrow depth range. Among western At- 
lantic species, S. nebulosus is unique in that its 
bathymetric center of occurrence (500-810 m) is 
nearly completely allotopic from that of its western 
Atlantic congeners. Nor does any other western At- 
lantic Symphurus have as wide a bathymetric range 
as S. nebulosus. The approximately 600-m-wide 
depth range noted for this species is typical for most 
other deep-water tonguefishes with the 1-2-2 ID pat- 
tern in other geographic regions (Munroe, 1992). 
Presumably, in contrast to the more dynamic condi- 
tions on the inner continental shelf, environmental 
parameters in deep-sea environments are more uni- 
form over a broader depth range, with this unifor- 
mity over depth reflected in the distinctively broader 
depth range of deepwater tonguefishes. 
Topp and Hoff ( 1972 ) examined distributional pat- 
terns of 18 species of flatfishes, including those of 
five tonguefishes, inhabiting the inner continental 
shelf off west Florida. They concluded that through 
resource partitioning these flatfishes co-exist sym- 
patrically without competing for resources. However, 
any hypothesis that invokes ecological co-existence 
of multiple species as resulting only from reduced 
competition through resource partitioning completely 
ignores historical information about the species, es- 
pecially evolutionary information directly related to 
the distributional ecology of that species. 
Distributional patterns of western Atlantic 
tonguefishes have not been examined within the con- 
text of the evolutionary history of the genus. Although 
this information would best be analyzed within the 
framework of hypothesized relationships of the spe- 
cies, such an hypothesis of intrageneric relationships 
of species of Symphurus is unavailable. Information 
(Munroe, 1992) used to define species groups within 
Symphurus provides a preliminary framework to 
serve as a basis for proposing testable hypotheses 
regarding distributional ecology of these fishes. For 
example, members of each species group as defined 
by ID pattern have a bathymetric distribution some- 
what different from that of most other groups 
(Munroe, 1992). Species with the 1-4-3 ID pattern 
are primarily shallow-water inhabitants with most 
member species commonly inhabiting depths shal- 
lower than 100 m ( S . oculellus to 110 m). Several 
species with this ID pattern, in fact, occur within 
estuarine and extremely shallow (<1 m) coastal en- 
vironments. Species with a 1-4-2 ID pattern occur 
predominantly on the inner continental shelf. West- 
ern Atlantic species with the 1-3-2 ID pattern inhabit 
a bathymetric range from ca. 1 to 750 m, but most 
occur in deeper waters (between 30 and 200 m) on 
the continental shelf. There are two ecological groups 
of species with this ID pattern that have quite dif- 
ferent bathymetric distributions. Species possessing 
the 1-3-2 ID pattern and a black peritoneum live on 
the continental shelf: S. pelicanus (30-150 m); S. 
pusillus (100-233 m); S. ginsburgi (110-300 m); S. 
billykrietei (48-650 m); S. stigmosus (192-373 m), 
S. piger (92-549 m), and <S. marginatus (37-750 m). 
Two dwarf western Atlantic species with this ID pat- 
tern and an unpigmented peritoneum inhabit rela- 
tively shallow (1-45 m) sandy substrates adjacent 
to coral reefs, almost exclusively in habitats at insu- 
lar locations through the Caribbean Sea. Two other 
dwarf species of Symphurus characterized by the 
1-3-2 ID pattern and an unpigmented peritoneum 
also inhabit similar depths at central and eastern 
Atlantic islands (Munroe, 1990). Species with a 1-3- 
3 ID pattern, such as S. trewavasae, the only west- 
ern Atlantic Symphurus with this ID pattern, typi- 
cally are found from about 30 to 100 m. The deepest- 
dwelling Symphurus species are those with 1-2-2 ID 
pattern, such as S. nebulosus , the only western At- 
lantic species with this pattern. No other western 
Atlantic Symphurus occurs as deep or has as wide a 
bathymetric range (239-810 m) as does S. nebulosus. 
Two other general patterns regarding the distri- 
butional ecology of Atlantic tonguefishes became 
apparent when data were examined within the com- 
parative context of the species groups identified by 
ID patterns. First, sympatric members of a species 
group do not occur syntopically, especially as adults. 
They either inhabit different depth zones, or if they 
occur at similar depths within the same geographic 
region, they are found on different substrates. Sec- 
ond, allopatric members of a species group are usu- 
ally found at similar depths (and possibly also on 
similar types of substrates). These general patterns 
of sympatric and allopatric distributions are exem- 
plified within each species group occurring in the 
Atlantic. For example, S. nebulosus occurs on soft 
mud bottoms at 239-810 m. Its bathymetric occur- 
rence is nearly completely allotopic in comparison 
with that of all other western Atlantic tonguefishes. 
The only other Atlantic symphurine tonguefishes in- 
habiting similar depths are the eastern Atlantic S. 
ligulatus and S. uanmelleae (Munroe, 1992), which 
have a 1-2-2 and 1-2-2-1-2 ID pattern, respectively. 
Although all three species inhabit similar depths, they 
are entirely allopatric geographically. Symphurus 
ligulatus occurs in the Mediterranean and off the west 
coast of North Africa, whereas S. vanmelleae occurs 
off the west coast of equatorial Africa (Munroe, 1990). 
Nine western Atlantic species have a 1-3-2 ID pat- 
tern, three others occur in eastern and central re- 
