18 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 124 



developed an approximately 2 : 1 ratio between rays and vertebrae 



(fig. 16). 



Specimens of Brotula multibarbata in the Honolulu aquarium, 

 though they remained with the body curved and in contact with the 

 substrate during the period I was able to observe them, continually 

 passed undulations along the free portions of the dorsal and anal fins. 

 Suggestions of similar fin undulations are found in the observations 

 of living brotulids by Whitley (1935) and Dawson (1966). This is 

 not to say that all brotulid locomotion is carried on by fin undulation 

 alone, for all brotulids can doubtless undulate the body in coordination 

 with the fins and probably do when greater speed is needed. Certainly 

 such coordination occurs in ophidiids (Herald, 1953; and Briggs and 

 and Caldwell, 1955) and carapids (Arnold, 1956). 



Phylogenetically, the argument regarding ophidioids herein ad- 

 vanced is not that they all swim in a manner very different from, 

 say, the zoarcids (which have a 1 : 1 fin ray to vertebra relationship), 

 but that their capability for independent fin undulation has led 

 toward a morphological endpoint contrary in direction to that at 

 which the basal percoids (with about 1.1 or 1.2 fin rays per vertebra) 

 almost have arrived, and in a direction that has been followed by 

 relatively few other percoid derivatives. Consequently, this develop- 

 ment (of an approximately 2 : 1 fin-ray-to-vertebra ratio) in ophi- 

 dioids appears to be systematically significant. 



With regard to the sensory peculiarities of the ophidioid fishes, 

 it seems to me that these are basic and that most, if not all, of the 

 other ophidioid specializations are secondary to and related to them. 

 Because of this, certain structural complexes that are not in themselves 

 strictly sensory will be included in the discussion here. 



Morphologically, one of the peculiarities common to all brotulids, 

 ophidiids, Gadopsis, and certain gadids, e.g., Urophycis, is the develop- 

 ment of the pelvic fin into one or two well-developed filaments 

 originating more or less far forward. Functionally, the pel vies of 

 brotulids and ophidiids have not been studied beyond the few pre- 

 liminary observations of Herald (1953) and Briggs and Caldwell 

 (1955). The function of the Urophycis pel vies, however, has been the 

 subject of an excellent recent investigation by Bardach and Case 

 (1965). 



With regard to behavior, Bardach and Case (1965, p. 198) wrote in 

 part: 



Fishes swimming along the bottom ordinarily direct their [pelvic] fins forward, 

 with the branches spread apart to an angle of up to 45°, the entire fin sweeping 

 from slightly forward of the snout back toward the flank (Fig. 5) [their figure]. 

 Each fin encompasses an arc of approximately 120° ahead and to the side of the 

 fish. Upon touching a morsel of food with a fin tip, the fish often has to back up 

 to veer down and ingest what it found. 



