ictalurids and a variety of other catfishes (Lundberg 1982). Little variation in the 

 appearance of the opercular bones was observed among species. 



Hyoid and Branchial Arches ^ :• 



Ferraris (1988) found that ageneiosids have a number of uniquely derived 

 features of the hyoid arch and branchial series. The hyoid arch consists of the 

 unpaired urohyal and paired hypohyal, ceratohyal, interhyal, epihyal, and 

 branchiostegal bones. The urohyal is broadly rounded anteriorly, with a long, 

 laminar projection posteriorly (Fig. 12). Anteromedially, the urohyal has a vertical 

 extension that projects between the hypohyals, which Ferraris (1988) regarded as a 

 synapomorphy of ageneiosids. Anteriorly, the ceratohyal is sutured to the ventral 

 ossification of the hypohyal along its ventromedial surface. This was also regarded 

 by Ferraris (1988) as a synapomorphy of ageneiosids, in comparison to the condition 

 of other doradoids, in which the two bones are separated by a large bar of cartilage 

 along their lateral surfaces. Posteriorly, the ceratohyal articulates both suturally and 

 synchondrally with the interhyal. The interhyals is a relatively long, rectangular 

 bone, slightly tapered at the posterior corner. The epihyal is a small osseous nodule 

 at the medial face of the hyomandibula, near its anteroventral suture with the 

 preopercle. * 



The ceratohyal supports up to six or seven branchiostegals, with the 

 remaining ones supported by the interhyals. The number of branchiostegals in 

 ageneiosids ranges from seven to twelve, and is of some use in distinguishing 

 species. However, there is a fair amount of intraspecific variation. Most species 

 have between eight and ten branchiostegals. Ageneiosus brevifilis andy4. marmoratus 

 have modal counts of eleven branchiostegals, followed hy A. pofystictus, A. 

 ucayalensis, and^. valenciermesi, all with modal counts of ten branchiostegals. 



