77 

 Chin barbels 



One of the most surprising and significant findings of this study was the 

 discovery that juveniles of several species oiAgeneiosus have barbels on the chin. 

 Unfortunately, adequate developmental series of juveniles were unavailable in the 

 collections examined to thoroughly elucidate ontogenetic changes in the barbels. 

 Nevertheless, it appears that some, and perhaps all species begin life with at least a 

 single pair of chin barbels, which are subsequently resorbed during growth. There is 

 little consistency in the literature associated with terminology of the chin barbels. 

 As used here, the term mandibular refers to the anterior pair of barbels, situated 

 nearest the lower lip, and the term mental is applied to the posterolateral pair, 

 nearest the posterior edge of the dentaries; a similar distinction in terminology was 

 made by Schaeffer et al. (1989), although the position, and, possibly, the ontogenetic 

 derivation of the barbels in the taxa they studied (Scoloplax spp.) is considerably 

 different than in ageneiosids. Initially I only observed the mental pair of barbels, 

 but examination of additional specimens revealed two pairs of chin barbels. In one 

 postl&TvalAgeneiosus sp. (MCNG 7595; 20.4 mm SL), there is a pair of relatively 

 long, fleshy mental barbels, medial to the dentaries and at a plane about equal with 

 the front margin of the eyes, and a pair of shorter mandibular barbels, near the edge 

 of the lower lip (Fig. 14a). A somewhat larger specimen (43.8 mm SL) from the 

 same collection lacks the mandibular pair, and the mental barbels are considerably 

 shorter relative to the length of the head (Fig. 14a). There apparently is 

 considerable heterochrony involved in the resorption of both pairs of chin barbels 

 among species. One relatively large specimen (80 mm SL) of A. pardalis has both 

 pairs of barbels (Fig. 14b), whereas none of six specimens of A. ucaycdemis (several 

 lots; 44-73 mm SL) show traces of either pair. In two specimens of ^4. vittatus 

 (MCNG 1477; 39.9 and 43.3 mm SL) the mental barbels are reduced to minute 



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