Studies are lacking for many species, and, within nearly all families, there is still a 

 tremendous dearth of information on inter- and infraspecific variation, ontogenetic 

 changes, and genetic and ecological plasticity. Consequently, there are few 

 uniformly accepted concepts of relationships among species, genera, and even 

 famiUes, despite the fact that many of the groups form distinctive, putatively 

 monophyletic clades. Fortunately, there has been a recent surge of systematic 

 interest in neotropical siluroids, and valuable comparative data are becoming more 

 readily available. Nevertheless, large voids remain in our understanding of 

 relationships and the distribution of character states, resulting in considerable 

 confusion and, occasionally, conflicting information of anatomical terminology or 

 taxonomic nomenclature. . , 



In the following summary, the general features of ageneiosid morphology are 

 presented. Wherever possible, inferences regarding the hypothesized polarity or 

 transformation of a structure is advanced on the basis of evidence provided from 

 literature sources, or direct observations from outgroup taxa. In addition to a 

 discussion of the morphological features associated with sexual dimorphism, a 

 detailed review of the available hterature on the reproductive biology is provided. 

 '".■■' ' - *w »--. ■ ,. -- ' '~. , ■ ■ , ■ 



"" Physiognomy ^ ■> ! 



Ageneiosids have a rather unusual general body appearance that is atypical 

 of most extant siluroids. They are characterized by flattened heads with laterally 

 directed eyes (Fig. 1), an extremely laterally compressed body, their reduced 

 barbels, and relatively short adipose and dorsal fins. Alexander (1965) remarked 



that: 



the Siluridae and Schilbeidae differ markedly in shape from typical 

 catfish...Though the head is depressed and the mouth wide, the trunk 

 is strongly compressed. The anal fin is very long, and the body cavity 

 is accordingly short. The adipose fin is very small or absent, and the 

 dorsal fin tends to be small. The similarities between these families 



