briefly discussed problems of determining homologies of the barbels, and 

 recommended that future studies include data about supporting tissues. 



Tetranematichthys differs from all other ageneiosids in having a single pair of 

 chin barbels in adults. These barbels have a peculiar frilled tip (Fig. 15), and 

 roughly correspond in position to the mental pair ofAgeneiosus. No small juveniles 

 of Tetranematichthys were available, so it remains unknown if more than one pair of 

 chin barbels is present during early ontogeny in this species. Presumably, the 

 retention of mental barbels in adults, albeit reduced in size, and the absence of the 

 mandibular pair, represents a more primitive state than that found in Ageneiosus. 

 Among other neotropical catfishes, only the auchenipterid Gelanoglanis has a single 

 pair of chin barbels, but Ferraris (1988) regarded the presumed loss of one pair of 

 barbels in Tetranematichthys and Gelanoglanis to have occurred independently. The 

 papillate tip of the chin barbel in Tetranematichthys has not been observed, to the 

 best of my knowledge, in any other auchenipterid, and is presumably an apomorphy 

 of this taxon. Its function remains unknown, although SEM photomicrographs 

 indicate that it is covered with tastebud-hke projections. Many doradids have 

 superficially similar frilled barbels, but they are generally much larger and lack the 

 filamentous stalk as in Tetranematichthys; their branched structure is herein 

 considered to have been independently derived. 



Maxillary barbels 



Unlike other doradoid catfishes, ageneiosids have inconspicuous, diminutive 

 maxillary barbels that are normally concealed within deep clefts above the comers 

 of the upper lip. This is the condition in females and nonbreeding males, and is the 

 reason why they have occasionally been overlooked by some investigators. 

 Reduction in size of the maxillary barbels is regarded as a derived state of the 



i- 



