traditionally been diagnosed as lacking all barbels except the maxillary pair. All 

 auchenipterids (sensu lato) have two pairs of chin barbels, with the exception of 

 Gelanoglanis stroudi (Bohlke 1980), which, like Tetranematichthys, has only a single 

 pair. However, these two taxa are apparently not closely related; Gelanoglanis was 

 placed in a clade with five other genera in the reelevated family Centromochlidae 

 by Ferraris (1988). — . , - .- - ,.- 



The loss of chin barbels in Ageneiosus is thought to be a derived reduction 

 from a primitive state, in which there is at least one pair in all other catfishes except 

 diplomystids and a few unrelated taxa that have independently lost the chin barbels. 

 Ferraris (1988) interpreted the presence of a single pair of mental barbels as an 

 autapomorphy for Tetranematichthys, and assumed that it was independently derived 

 only in Gelanoglanis among other neotropical catfishes. However, there is 

 ontogenetic evidence that postlarval v4^me/o5z/5 have a mental barbels that are 

 resorbed during early development (see morphological comparisons for a more 

 detailed discussion). Therefore, it is more parsimonious to conclude that retention 

 of mandibular barbels in adults of Tetranematichthys represents a plesiomorphic 

 condition within the ageneiosid clade, although their unique morphology may be an 

 independent derivation. Moreover, Tetranematichthys exhibits additional primitive 

 characters among ageneiosids, including a large swimbladder, untoothed maxillary 

 barbels in nuptial males, and a postcleithral process. Thus, the genus is diagnosed 

 primarily on the basis of primitive character states. 



From the standpomt of nomenclatural stability, nevertheless, it seems 

 desirable to retain the generic status of Tetranematichthys. In spite of its probable 

 basal position among ageneiosids, T. quadrifilis is a highly distinctive species with no 

 obvious close relative among the remaming ageneiosids. Although the relationship 

 of this species to other neotropical siluroids has until recently been questionable, 



