f--' ;. ■ .. .. ■ - ■-• ■ ■ - ■ ■ ^-., ■;■>, ^' 32 



instance, in the smallest specimen oiA. brevifilis examined (MZUSP 9384, 77 mm 

 SL), the swimbladder is large (6,5 mm long) and has pliable anterior chambers, but 

 in adults the swimbladder is greatly reduced and encapsulated by a superficial 

 ossification of the compound vertebral centrum (see Fig. 8 in anatomical 

 description). Ferraris (1988) noted that swimbladder encapsulation iny4. 

 marmoratus occurred at a slightly larger size (170 mm SL) than in A. ucayalensis and 

 A. guianensis ( =A. ucayalensis) (120 mm and 92 mm SL» respectively). Variation of 

 swimbladder morphology among species is discussed in greater detail in a separate 

 section. ■ : " ' 



In its original context, the genus Tympanopleura was diagnosed on the basis 

 of having a large, unencapsulated swimbladder, evident externally as a window or 

 "tympanum" in the lateral epaxial musculature immediately posterior to the 

 operculum and just below the dorsal fin and above the pectoral fin. This feature is 

 not unique to Tympanopleura and, in fact, is found in most if not all catfishes lacking 

 unencapsulated swimbladders. As Alexander remarked, ^ 



■ . \- ..■■ ■- " ■ - -i V ^i ■ .' - 



in some Cyprini...muscle is absent from a patch of body wall lateral to 



., the anterior end of the swimbladder... This condition seems to be 



universal in Siluri. The muscle-free areas of skin are bounded 



anteriorly by the post-temporals and cleithra, and dorsally by the 



,,, expanded parapophyses when these reach to the skin. Bridge «fe 



Haddon (1894) call them the 'lateral cutaneous areas'. The 



; ; swimbladder lies very close below them. A littie loose fatty 



connective tissue hes between swimbladder and dermis at the edges of 



this area. (Alexander 1964a:425) 



In his study of functional morphology in catfishes, Alexander further stated, 



; ; ■ In catfish, muscle is absent from a patch of body wall (the lateral 

 : cutaneous area) on each side lateral to the anterior end of the 



J . • swimbladder. These areas serve to reduce the impedance of the body 

 wall to changes of swimbladder volume, and so increase the sensitivitj' 

 of the Weberian apparatus. (Alexander 1965 : 109) 



