324 



Distribution 



Ageneiosus brevifilis is the most widespread species of the genus, occurring 

 throughout most of the major lowland rivers of South America (Fig. 56). It is 

 widespread and relatively common throughout both the Amazon and Orinoco rivers 

 and their major tributaries. In the Amazon at least, there are more records of the • 

 species in the middle and lower portions of the basin, although this may reflect more 

 intense fishing exploitation and collecting efforts rather than actual abundance or 

 distribution. The species is widespread and relatively common in rivers draining the 

 northern and eastern section of the Guiana shield, and it is also present in the Rio 

 Negro drainage. To the south, ^. brevifilis is present in the large north flowing rivers 

 that drain into the Amazon, including the rios Madeira, Tapajos, Xingu, and 

 Araguaia. The species is also distributed widely throughout the Rio Parana- 

 Paraguay basin, where it andy4. ucayalensis are the only sympatric congeners ofy4. 

 valenciennesi. 



Etymology 



From the Latin brevis, meaning short or small, and filum, meaning a thread 

 or string, in reference to the maxillary barbels, the small size of which was 

 erroneously believed to be characteristic of both sexes of the species by early 

 authors, who failed to observe ossification of the barbels in nuptial males. The 

 subgenus Pseudageneiosus, from the combined formpseudes, meaning false, and the 

 stem of the genus, further emphasizing reduction of the barbels. 



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