58 



as in most other catfishes. However, perhaps one of the most important sensory 

 aspects of these fishes may be electroreception; a survey of many catfishes has 

 revealed that ageneiosids have among the most highly developed acoustic tubercles 

 in the central sensory areas of the brain, which have been impUcated in very low 

 threshold electroreception (R. J. Miller, unpublished data, personal 



correspondence). 



■ ■"-". 1 " '■- r , ■' - ■ ■■ ^ 



Infraorbital and Laterosensory Canals 



Primitively among ostariophysans, the ossicles surrounding the infraorbital 

 branch of the latero-sensory canal system, commonly called infraorbitals or the 

 infraorbital series, are relatively large bony plates covering portions of the cheek 

 adductor musculature (Fink and Fink 1981). In catfishes, the infraorbitals are 

 reduced to the canal-bearing portions of the bones, although plate-Uke elements 

 have been secondarily derived in loricariids and callichthyids (Fink and Fink 1981, 

 Schaeffer 1987), and, to a lesser extent, in doradids (Eigenmann 1925). There is 

 extensive variation in the number of infraorbitals among catfishes in general, and 

 the homologies of individual elements has never been thoroughly estabUshed. The 

 primitive number of infraorbitals in siluroids is thought to be five (Lundberg 1982), 

 including the anteriormost ossicle, which is uniformly termed the lacrimal. This 

 represents a reduction of two from the presumed primitive teleost number of seven 

 (Nelson 1969), due to loss or fusion of the antorbital with the lacrimal and the 

 dermosphenotic with the chondral portion of the sphenotic. 



There is extensive variation in the shape and number of the infraorbital 

 bones among doradoids (Ferraris 1988). The primitive number, as in other 

 catfishes, is believed to be five. Ferraris (1988) concluded that doradids and 

 ageneiosids share a derived condition of having lost an additional element, which he 



