101 



Entomocorus have posterior caecae (Fig. 20a,b), a presumably primitive condition 

 shared with A. pardalis andA.pipercUus. The extremely large, single sac in 

 Tetranematichthys is milike the shorter, paired caecae found in the remaining 

 species ofAgeneiosus, and possibly represents a separately derived state. 

 Ageneiosids with encapsulated swimbladders have concommitant 

 modifications of the transverse processes of the fourth vertebra, involved in 

 formation of the ESA, as detailed below in a discussion of the Weberian apparatus. 

 In these taxa, there is a moderately large anterolateral foramen in each side of the 

 swimbladder capsule, where the Miillerian rami contact the membranous tunica of 



•r J- • 



the swimbladder, " ' / 





./ "^ i. ' Dorsal Fin 



The ageneiosid dorsal fin consists of one small spinelet, one large defensive 

 spine, and six branched rays and their associated proximal supporting structures. 

 The entire fin is relatively small and situated anteriorly, above the pectoral-fin 

 origin and immediately behind the supraoccipital. 



The first lepidotrichium, which normally forms part of the locking 

 mechanism in siluroids (Alexander 1965), consists in ageneiosids of a bifurcated 

 bone with strongly recurved ventral limbs (Fig. 22), similar to that found in other 

 doradoids (Royero 1987, Ferraris 1988). The curved shape of the first dorsal spine 

 also resembles that of some eastern hemisphere catfishes (members of the 

 Mochokidae and Sisoridae), but the phylogenetic significance of this similarity, if 

 any, is not known (Ferraris 1988). ' 



The second lepidotrichium typically forms a relatively elongate, stiffened 

 spine; in females and non-nuptial males, this element generally consists of a thin 

 spine with a single row of moderately weak, retrorse teeth along the proximal two 



