198 



ELOPIFORM FISHES 



elopids, are given below (Table I). 

 specialized. 



In all these features the megalopids are more 



Table I 





Differei 



ices between the Elop 



idae and the Megalopidae 





Character 



Elopidae 





Megalopidae 



i. 



Body 



Rounded 





Compressed 



ii. 



Neurocranium 



Shallow 





Deepened 



iii. 



Quadrate/mandibular 

 articulation 



Behind level of eye 





Beneath eye 



iv. 



Middle pit-line 



Present 





Absent 



v. 



Autosphenotic spine 



Weakly developed 





Well-developed 



vi. 



Epiotic process 



Weakly developed 





Well-developed 



vii. 



Post-temporal fossae 



Reaching anteriorly 



to the 



Reaching anteriorly to the 







level of the autosphenotic ; 



level of the orbitosphenoid ; 







never confluent 





confluent in those that can be 

 examined in this respect 



viii. 



Intercalar 



Moderately large 





Large and of complex shape 



ix. 



Otophysic connection 



Absent 





Present 



X. 



Rostral ossicles 



Two 





One, representing the more anterior 

 of elopids 



xi. 



Pelvic fins 



Originating beneath 



or 



Originating beneath or anterior 







posterior to the dorsal fin 



to the dorsal fin 



xii. 



Anal fin 



Short based, first 

 pterygiophore short 





Long based, first pterygiophore 

 long 



xiii. 



Scales 



Lateral line tubes 





Lateral line tubes branched 



unbranched 



Trends within the Megalopidae include : the enlargement of the post-temporal 

 fossae with a corresponding increase in the convexity of the skull roof ; reduction of 

 parasphenoid teeth ; the development of a superior mouth and the development 

 of a large coronoid process on the mandible. 



The megalopid neurocranium has been modified in response to the forward exten- 

 sion of the swimbladder and epaxial musculature. In primitive teleosts the bulk 

 of the epaxial musculature extends forwards into paired post-temporal fossae whose 

 anterior wall is formed by the autosphenotic of either side. In Recent megalopids 

 these fossae have become enlarged so that the anterior wall of the fossa is formed by 

 the orbitosphenoid and the fossae of either side are confluent above the cranial vault. 

 The vertical depth of these fossae has also increased resulting in greater convexity 

 of the skull roof in the otic region. Many teleosts have retained post-temporal 

 fossae, but the enlargement of these vacuities is a feature unique to the megalopids. 

 Some other groups, e.g. salmonids and ichthyodectids, have supplemented the post- 

 temporal fossae by the development of grooves upon the roof, while a general ten- 

 dency among clupeomorphs and more advanced protacanthopterygians is to erode 

 the roof so producing a post-temporal groove. 



The otophysic connection of the Megalopidae is of a simple type, totally unlike 

 that found in other groups possessing a swimbladder-cranial linkage (clupeomorphs, 

 notopteroids and juvenile mormyriforms, Greenwood et at. 1966). Although the 



