consider an increase in number of vertebrae as derived, the most extreme condition 

 therefore being shared by A. brevifilis,A. mannoratus,A.pofystictus, and the large- 

 bodied, fork-tailed species, all of which have a mean number of total vertebrae 

 exceeding 49. Among doradoids in general, an increase in vertebrae may represent 

 a shared character at a higher level of universality, but, until more complete data 

 are available, I defer making any comparisons outside of Ageneiosus. 



The ribs of ageneiosids, like other catfishes, are pleural. The first rib 

 articulates with the transverse process of the sixth vertebra. The basal end of the rib 

 is curved and hooks around the tip of the transverse process in a manner that is 

 unique to doradoids (Ferraris 1988). The number of paired ribs in most species of 

 ageneiosids varies by two or three, but the modal value is useful in separating some 

 species. The number of ribs parallels the number of branchiostegals among species, 

 with the fewest in small species and the most in A. brevifilis and^l. marmoratus. Few 

 comparative data are available for outgroups, although a survey by Britski (1972) 

 indicated that most auchenipterid genera have between six and thirteen pairs. An 

 increase in the number of ribs is probably derived, at least within ageneiosids, and 

 may be correlated with expansion of the coelomic cavity associated with increased 

 body length. 





- i 



■^v' 



^^■* 



Swimbladder 









•. ■ '->' %\f 









The ageneiosid swimbladder has been the subject of considerable attention, 

 stemming from the fact that most species, when originally described, were known or 

 thought to have a very reduced swimbladder that was encased in a bony capsule 

 associated with the complex centrum (the encapsulation process is discussed below). 

 The original description of Tetranematichthys {as Ageneiosus quadrifilis; Kner 1858a) 

 was accompanied by an illustration of that species' swimbladder, which is large, 



