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PACIFIC SCIENCE, Vol. XX, October 1966 
arrangement of families proposed by Regan 
ostensibly on the basis of the axillary scaly 
process. This postulate requires amplification 
and clarification in several respects. 
In the first place, it has been hypothesized 
that the presence of an axillary process is an 
inherited character and that its loss in the per- 
coids has been secondary. On the other hand, 
those fishes that have retained the process in- 
clude the forms which have developed much 
the most specialized jaw structure. I can see no 
causal explanation for this divergence of evolu- 
tionary direction and must fall back on the fact 
that functionally independent and nonpleiotrop- 
ically controlled characters evolve indepen- 
dently. It may be instructive, therefore, to dis- 
cuss separately the assumed evolutionary se- 
quence in axillary process loss and jaw structure 
specialization. 
Axillary processes, if inherited in percoids as 
here believed, would seem to have been lost 
many times under varied circumstances. Among 
the Beryciformes a minute-scaled Paratrachich- 
thys lacks axillary processes, as do all other 
groups known to me that have very small 
scales or none at all. Among the Mugiliformes 
Sphyraena lacks axillary processes ; and, whether 
there is a causal relationship or not, all fast- 
swimming fishes except the Bramidae and Pem- 
pheridae lack processes, e.g., Carangidae, Cory- 
phaenidae, Scombroidei. Again, all fishes that 
prop themselves off the bottom by the pelvic 
fins lack axillary scales, e.g., Blenniidae, Cir- 
rhitidae as well as all fishes that have modified 
or reduced pelvics, e.g., Gobioidei, Ophidioidei. 
Indeed, since apparently all families above the 
Percoidae except the Pomacentroidae and La- 
broidae lack axillary processes, the major prob- 
lem is perhaps that of why so many percoid 
families have them. To this question there is, to 
my knowledge, no answer worth writing. 
A related matter for which I know no solu- 
tion is why Regan (1913) excluded "a few of 
the more aberrant families” from his division 
between those percoids with, and those with- 
out, an axillary process. The families so ex- 
cluded are apparently the Cepolidae, Cichlidae, 
Oplegnathidae, Nandidae, and Pristolepidae 
(with all of which I have very little familiar- 
ity). 
With regard to the jaws and teeth, those of 
Roccus and Perea (without axillary processes) 
and those of Lates and Pempheris (with axillary 
scales) would seem to be very similar and about 
equally generalized. There appears to be no 
morphological reason why the jaw structure of 
any of the four genera should not have devel- 
oped on the one hand the specializations of 
Epinephelus (without axillary processes) or on 
the other the peculiarities of Kyphosus or Chae- 
todon (with axillary processes). What does 
seem clear is that the jaw structure of Epi- 
nephelus could not directly have given rise to 
that of Kyphosus, or vice versa. Therefore it is 
somewhat disconcerting to find certain families 
with the jaw specializations of those families 
with an axillary process to be without such a 
process. Among such families would appear 
TABLE 2 
Trends of Development in Two Categories of Percoid Families 
AXILLARY PROCESS PRESENT AXILLARY PROCESS ABSENT 
Narrow-headed fishes, with the eye set well up and 
back on the head 
Feeding usually accomplished by nipping off or pluck- 
ing out individual items from their surroundings 
Carnivores, herbivores, or omnivores 
Mouth relatively small 
Jaw teeth often reduced to a single specialized row, 
conical, incisiform, molariform, or fused 
Jaws capable of relatively slight lateral expansion 
Maxillary shaft with little rotation when the mouth 
is opened, forming a supporting cap over the 
lateral end of the premaxillary 
Broad-headed fishes, with the eye set relatively far 
forward on the head 
Feeding usually accomplished by engulfing whole 
animals 
Carnivores 
Mouth often large 
Teeth conical, usually in bands, used for grasping 
prey 
Jaws capable of relatively great lateral expansion 
Maxillary shaft with considerable rotation when the 
mouth is opened, giving slight support to the 
lateral end of the premaxillary 
