102 



ONTOGENY AND SYSTEMATICS OF FISHES-AHLSTROM SYMPOSIUM 



0STE0GL05 - 

 SOMORPHA 



ELOPO- 

 MORPHA 



CLUPEO- 

 MORPHA 



EUTEL - 

 EOSTEI 



Fig. 53. Hypothesis of relationships between major groups of Tele- 



ostei. 



The unique structure of a leptocephalus can be appreciated best 

 in cross section (Fig. 54, left). The viscera lie along the ventral 

 margin in a narrow strand. The notochord, dorsal nerve cord, 

 and dorsal aorta lie together in the longitudinal axis of the body 

 about midway between the dorsal and ventral margins. The 

 myomeres form a thin layer on the outside. Filling the rest of 

 the interior of the body is an acellular mucinous material bound- 

 ed by a continuous layer of epithelial cells. The mucinous pouch 

 separates the viscera, the notochord and the two sides of the 

 body musculature from each other and gives form and rigidity 

 to the body. The characteristic shrinkage of the leptocephalus 

 at metamorphosis is due to the loss (presumably by resorption) 

 of the internal mucinous material. A typical clupeid larva such 

 as Elnaneus teres (Fig. 54, right) is constructed much differently. 

 Here there is no mucinous pouch. The notochord occupies a 

 large part of the cross-sectional area and is surrounded imme- 

 diately by the thick axial musculature to form a solid, compact 

 structure. The viscera lie immediately below the dorsal aorta. 

 Leptocephali have a small head and a set of long, sharp teeth 

 whose function is uncertain, since leptocephali do not seem to 

 be predatory. The basic structure of a leptocephalus is the same 

 whether it is an elopiform, notacanthiform or anguilliform. A 

 leptocephalus larva is known for every family of elopomorphs 

 except the rare, monotypic Myrocongridae, so the character 

 seems entirely inclusive of the group. Nothing even remotely 

 comparable is found outside the Elopomorpha. 



Fig. 54. Cross section through the bodies of a leptocephalus (Meg- 

 alops allanlictis) (left) and a clupeid larva (Elrumeus teres) (right). DA, 

 dorsal aorta; NC, notochord; SC, spinal cord. 



The leptocephalus, then, must be considered a true synapo- 

 morphy and powerful evidence in favor of the monophyly of 

 the Elopomorpha. Perhaps nowhere else in fish systemalics have 

 larval stages played a more important role. 



The Marine Biomedical Institute, The University of Texas 

 Medical Branch at Galveston, 200 University Boule- 

 vard, Galveston, Texas 77550. 



Ophichthidae: Development and Relationships 



M. M. Leiby 



THE family Ophichthidae, comprising approximately 250 

 nominal species and 53 recognized genera, is arranged in 

 six tribes and two subfamilies (McCosker. 1977) (Fig. 55). The 

 subfamilies, Myrophinae and Ophichthinae, are separated by a 



number of characters. All adult Myrophinae have a well-de- 

 veloped caudal fin which is continuous with the dorsal and anal 

 fin. Adult Ophichthinae, except for Echelus in the tribe Ophich- 

 thini and Lcptenchelys in the tribe Bascanichthyini, lack a caudal 



