Classification of Percoid Fishes — Gosline 
expanding the already broad gape even farther. 
The tremendous expansion of the open gape 
of Epinephelus seems to be at the end of one 
trend of jaw development. However, almost 
the same jaw construction and capabilities occur 
in the Beryciformes (e.g., Holotrachys) , Scor- 
paeniformes (e.g., Scorpaenopsis ) , etc. A fish 
with this type of jaw construction would seem 
well adapted to engulfing nearby objects of 
moderate to large size, especially those close to 
the bottom. There are, however, a number of 
things such a fish will not be able to do well. 
It has no method of selecting one particular 
food item from its immediate surroundings. 
Nor can it bite off a part of anything, e.g., a 
fisherman’s bait. Finally, such a fish probably 
cannot bite down on anything with much 
force; the length of the jaws militates against 
this, especially since the partly rotated maxilla- 
ries do not form a very firm support for the 
Fig. 2. Maxillary and associated features in Epi- 
nephelus with the mouth open, superior view. A, 
Adductor mandibulae muscle; L, ligamentum maxillo- 
mandibulare posted us of van Dobben (1935: Fig. 
5 ) : anteriorly it joins a ligament to the inner surface 
of the maxillary, above it is joined by a sheath to the 
adductor mandibulae, and posteriorly it is attached 
to the lower jaw (not shown) ; mx, maxillary; and 
sm, supramaxillary. 
415 
lateral ends of the premaxillaries when the 
mouth is open. 
Among perciform fishes with an axillary scaly 
process there are some basal families, e.g., Cen- 
tropomidae, Pempheridae, Bramidae, and per- 
haps Sciaenidae, in which no particular jaw 
specialization is apparent. But in the other fam- 
ilies there is a notable trend toward a single 
row of specialized teeth. Sometimes, as in the 
chaetodonts, these teeth are hairlike and are 
used for such purposes as separating the eggs of 
other fishes from the rocks on which they have 
been laid. In other families the teeth may be in- 
cisiform (Kyphosidae, Pomacentridae) , molari- 
form (Sparidae), or fused into a beak (Ople- 
gnathidae, Scaridae). Whatever the type of 
teeth, there are several features of head structure 
held in common by the more advanced perci- 
form fishes with axillary scales. One is that the 
mouth is always relatively small, with compara- 
tively little lateral expansion. The maxillary is 
more or less restricted to a single plane of 
movement, sliding up and down directly above 
the lateral ends of the premaxillary; it often 
forms a sort of cap fitting over the tip of the 
premaxillary, and in its most extreme develop- 
ment, i.e., in the Scaridae, the maxillary be- 
comes rigidly united to the premaxillary. With 
the restriction of the lateral expansion of the 
gape, the lacrimal (preorbital) frequently ex- 
tends down over the maxillary and premaxillary, 
completely covering them when the mouth is 
closed, e.g., as in Lutjanus. This lacrimal ex- 
pansion helps restrict the maxillary below it to 
a single plane of movement and inhibits rota- 
tion of the maxillary; it also carries openings 
of the lateral line canal down to just alongside 
the mouth (along the lower border of the ex- 
panded lacrimal). Finally, as the fishes in this 
group become smaller-mouthed, the mouth 
tends to move downward and forward and the 
eye up and back on the head. Sometimes, as in 
the labrid Gomphosus, the mouth seems to 
operate somewhat on the principle of long- 
handled forceps, or again, as in the labrid 
Epibulus , on the principle of a bellows. 
The jaw differences between the two main 
types of percoid fishes discussed in the preced- 
ing paragraphs are summarized in Table 2. 
In this paper an association has been postu- 
lated between certain aspects of feeding and an 
