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very similar in terms of physiognomy, coloration, and meristic counts to the fork- 

 tailed species with encapsulated swimbladders, and therefore is considered to be the 

 sister species to the lineage defined by an encapsulated swimbladder. • - 



Some of the extensive homoplasy of the character state data is reflected in 

 node C of the consensus tree, which includes an unresolved trichotomy involving ^4. 

 atronasus,A. brevis, andA.piperatus. All three species are diminutive and share the 

 plesiomorphically large, unencapsulated swimbladder. Ageneiosus brevis is the only 

 species of the genus that has a moderately developed postcleithral process (5, state 

 0), which is a primitive state shared with Tetranematichthys and all other doradoid 

 catfishes. Ferraris (1988) reported that he observed a postcleithral process in a 

 juvenile specimen oiA. marmoratus ( =A. vittatus ?), but that it was absent in a 

 larger specimen. Presence of the postcleithral process is variable in^. brevis, and 

 some populations have individuals with and without the structure. On the basis of 

 the postcleithral process alone, >!. brevis could be considered more primitive than 

 either v4. atronasus oxA.piperatus, but the latter taxa do not share any obvious 

 synapomorphies. In contrast, ^4. atronasus andy4. brevis appear to be sister species 

 by virtue of sharing the presumably derived pair of posterior swimbladder caecae 

 (not included in the numerical analysis). Paired swimbladder caecae are believed to 

 be absent in both A. piperatus and A. pardalis, but are present in all other species of 

 the genus, including those with encapsulated swimbladders. This character-state 

 distribution is difficult to account for. Ageneiosus pardalis shares a number of 

 features with a more inclusive clade (discussed above) than with A. piperatus; in fact, 

 these two species are phenetically very different, representing almost the full 

 extreme of morphological differences in the family (A. piperatus is the most 

 diminutive species and has a number of reductive character states, whereas yl. 

 pardalis is very large and has derived meristic states). Two explanations are possible 

 to account for the swimbladder caecae; the first is that paired caecae may have 



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