;;;, ,,., 103 



thirds or more of the posterior margin and weak crenulations along the basal 

 anterior margin. In nuptial males the dorsal spine is modified into an elaborate 

 mating structure, consisting of a long, sinuous spine with sharp, antrorse odontodes 

 along the anterior margin and a completely edentulate posterior margin (Fig. 23). 

 Several genera of auchenipterids are known to have similar dimorphism of the 

 dorsal-fin spine, although no information is available for many other species, due to 

 a lack of enough preserved museum material, and, possibly, to seasonality of 

 dimorphism. Ferraris (1988) considered dimorphism of the dorsal-fin spine to be a 

 synapomorphy of the family Auchenipteridae (in which he included ageneiosids), 

 despite an absence of data for many species. He further suggested that one group of 

 species in Trachelyopterus may have secondarily lost the dimorphic spine. Given a 

 putatively important role of the dimorphic spine of males during mating, it seems to 

 me that a secondary loss of this character is counter-intuitive. Rather, I suspect that 

 either the above clade of species is primitive with respect to this character, or, more 

 likely, that dimorphic males of the included species have simply not been observed. 

 In any case, sexual dimorphism of the dorsal-fin spine is unique to ageneiosids and 

 at least some auchenipterids, and, in combination with the large number of other 

 corroborative characters, supports a hypothesis that the included taxa are 

 monophyletic. , , . , . . 



Morphology of the dorsal spine is of limited use in distinguishing ageneiosid 

 taxa. Nuptial males of all species oiAgeneiosus have numerous sharp, antrorse 

 odontodes along most or all of the anterior margin of the dorsal spine, and an 

 edentulate posterior margin. In at least some species, these odontodes are 

 distributed in a basal cluster of laterally directed serrae, followed by a hiatus of no 

 serrae, and the distal half or more of the spine with antrorse serrae arranged in an 

 alternating anterolateral, sinistral-dextral fashion (Fig. 23). There may be some 

 species-specific differences in the arrangement of these odontodes; for instance, all 



