Classification of Percoid Fishes — Gosline 
413 
surroundings, as the chaetodontids and labrids 
do, or nip it off, as the scarids do. Their main 
problem is to get the mouth effectively shut over 
the selected item, and their front teeth are often 
specialized in various ways. 
In the above analysis two quite different 
methods of feeding have been contrasted. How- 
ever, among the less specialized percoids a fish 
that habitually feeds in one of these two ways 
may shift more or less easily to the other, and 
many percoids are opportunists, eating what 
they can find in whatever manner they can get it. 
The jaw mechanisms in the two groups just 
differentiated reflect their main feeding habits 
(or vice versa). Certain general attributes of 
jaw structure are held in common by all percoid 
fishes. Among these are the (usual) abilities 
(1) to bring the maxillary down across the 
corner of the mouth when the lower jaw is 
swung open, (2) to protrude the premaxillaries, 
and (3) to expand the oral cavity laterally as 
well as vertically. 
Although the more generalized percoids are 
quite similar to one another in jaw structure, 
rather different trends of development from this 
basal pattern are discernible in those fishes with, 
and in those without, an axillary process. In the 
"engulfing” forms (without an axillary pro- 
cess) the teeth do not become specialized and 
the jaw structure develops in one of two direc- 
tions. In such fishes as the carangid Scomher- 
oides (or Chorinemus') , which simply runs 
down its prey, premaxillary protrusion has been 
lost and the maxillary has become a simple 
strut above the premaxillary (Suzuki, 1962: 
Fig. 15F). In contrast, the serranid fishes of 
the genus Epinephelus perhaps represent the 
epitome of a trend toward a cavernous mouth 
opening. 
A comparison between Epinephelus s pilot o- 
ceps (without an axillary process) and Lutjanus 
vaigiensis (with an axillary process) may serve 
to exemplify the differences between the two 
groups. In specimens of both species 140-155 
mm in standard length the width of the gape is 
about the same when the mouth is closed (14- 
15 mm), yet when the mouth is opened wide 
the gape expands laterally only to 18 mm in 
Lutjanus but becomes a yawning chasm 30 mm 
across in Epinephelus. One factor that makes 
possible the relatively wide gape opening is the 
TABLE 1 
FAMILIES WITH A SCALY 
PROCESS IN THE AXIL 
OF THE PELVIC FIN 
FAMILIES WITHOUT A 
SCALY PROCESS IN THE 
AXIL OF THE PELVIC 
FIN 
Beryciformes 
Beryciformes 
Polymixiidae 
Holocentridae 
Trachichthyidae 
Mugiliformes 
Mugiliformes 
Mugilidae 
Atherinidae 
Polynemidae 
Sphyraenidae 
Zeiformes 
Antigoniidae 
Perciformes 
Perciformes 
Percoidei 
Percoidei 
Percoidae 
Percoidae 
Centropomidae 
Percichthyidae 
Bramidae 
Serranidae 
Pempheridae 
Plesiopidae 
Arripididae 
Acanthoclinidae 
Lutjanidae 
Kuhliidae 
Scorpididae 
Centrarchidae 
Nemipteridae 
Priacanthidae 
Pomadasyidae 
Cepolidae 
Toxotidae 
Rainfordiidae 
Monodactylidae 
Apogonidae 
Lobotidae 
Percidae 
Lethrinidae 
Lactariidae 
Kyphosidae 
Labracoglossidae 
Dichistiidae 
Bathyclupeidae 
Girellidae 
Pomatomidae 
Sparidae 
Rachycentridae 
Centracanthidae 
Carangidae 
Emmelichthyidae 
Menidae 
Leiognathidae 
Coryphaenidae 
Sciaenidae 
Nandidae 
Mullidae 
Cichlidae 
Chaetodipteridae 
Sillaginidae 
Drepanidae 
Branchiostegidae 
Scatophagidae 
Cirrhitoidae 
Chaetodontidae 
Cirrhitidae 
Enoplosidae 
Cheilodactylidae 
Histiopteridae 
Trachinoidae 
Oplegnathidae 
Parapercidae 
Pristolepidae 
Embiotocoidae 
Pomacentroidae 
Embiotocidae 
Pomacentridae 
Notothenioidae 
Labroidae 
Nototheniidae 
Labridae 
Acanthuroidei 
Scaridae 
Acanthuridae 
Zanclidae 
Siganoidei 
Siganidae 
Scombroidei 
Scombridae 
Stromateoidei 
Nomeidae 
Anabantoidei 
Anabantidae 
