:y '. ■ -■•-. ■■ 99 



number of other catfishes, there are accessory caecae or diverticuli, which I consider 

 to be derived in those taxa with them. Many species of doradids have very elaborate 

 accessory chambers (Eigemnann 1925), but their condition is herein considered to 

 be independently apomorphic from that in ageneiosids, 



Tetranematichthys quadrifilis has a very unusual swimbladder, consisting of a 

 very large, oval, semi-turgid anterior chamber, and an equally large, fleshy posterior 

 caecum (Fig. 20c); presumably, the swimbladder is hydrostatically functional, and it 

 may also be involved in sound production (as evidenced by the large ESA, discussed 

 below). "• -^";;i:- . ': . • ' ■ ' v ' 



' , ^°"^ species oiAgeneiosus have large, unencapsulated swimbladders as 

 adults: atronasus, brevis, pardalis, a.nd piperatus. The first two have posterior caecae, 

 which are short and broad in^. atronasus, but somewhat more variable in A. brevis, 

 some specimens of which have considerably shorter caecae than illustrated in Fig. 

 20e. Limited material of A. piperatus prevented a detailed study of the swimbladder 

 in this species; however, it apparently has a very large, spherical swimbladder, 

 without posterior caecae, as observed in one paratype (CAS 58382; 47 mm SL). 

 Perhaps the most atypical species is A. pardalis, which has a relatively large, turgid, 

 unencapsulated swimbladder without any posterior caecae, a condition that defies 

 the general trend of a negative correlation between swimbladder size and maximum 

 body size observed in other species, \ 



The remaining species all have encapsulated swimbladders as adults (Fig. 

 21). The capsule is similar in shape among all of these, although slightly variable; 

 the caecae in A. vittatus are slightly longer and more divergent than in the other 

 species. '■■ ;■ » ' ! ' ' ' ■ 



I consider encapsulation of the swimbladder in some ageneiosids to be a 

 shared, derived character. Encapsulation is well known in a variety of other taxa 

 (Alexander 1964, Howes 1983), many of which are benthic and often rheophihc. 



;ioi;^ 



