126 



ONTOGENY AND SYSTEMATICS OF FISHES -AHLSTROM SYMPOSIUM 



place the clupeomorpha nearer to the next most advanced clade, 

 the Euteleostei, than to the next least advanced clade, the Elo- 

 pomorpha. 



Evidence from eggs and larvae 



Relevant ontogenetic evidence concerning the relationships 

 of the Clupeiformes is meager. Elopiform eggs are unknown. 

 Anguilliform eggs resemble clupeid eggs in having perivitelline 

 spaces, segmented yolks, and may have oil droplets. Eel eggs 

 can be much larger than herring eggs: 5.5 mm diameter in A/m- 

 raena. 2.43 mm in an anguillid (Ahlstrom and Moser, 1980). 

 Osteoglossomorphs have pelagic or demersal eggs which may 

 be 0.5-4.0 mm in diameter, may be dark blue, and may have 

 a very wide perivitelline space as in Hiodon (Breder and Rosen, 

 1966). The coincidence of demersal adhesive eggs in both the 

 osteoglossomorphs and the Dorosomatinae is extremely un- 

 likely to be a shared derived character from a common ancestor. 

 Clupeid and anguillid eggs are considered unspecialized relative 

 to eggs of the higher teleosts (Ahlstrom and Moser, 1980). Very 

 little else may be said. Perhaps electron microscopy will reveal 

 patterns of chorion sculpturing which will be informative. 



The larvae of Clupeiformes are unspecialized and undergo a 

 fairly uneventful metamorphosis. The migration of the dorsal 

 fin during transformation also occurs in the elopiforms. The 

 larva of Chanos. a primitive gonorynchiform (Fink and Fink, 

 1981), superficially resembles clupeids or engraulids but appar- 

 ently does not have the same migration of the dorsal fin (Rich- 

 ards, this volume). 



If the Elopomorpha and the Clupeomorpha share a common 

 ancestor it is possible that the Clupeomorpha retained the un- 

 specialized, rapidly developing larvae while the adults evolved 

 towards a specialized schooling planktivore body plan. The lep- 

 tocephalus found in the elopiforms, albuliforms, and anguilli- 

 forms could have evolved for dispersal or to reduce predation 

 or to take advantage of larval drift the way Angntlla does in the 

 North Atlantic and the way herring do in the North Atlantic 

 with their circuit of migration (Cushing, 1977). The leptoceph- 

 alus could have arisen in the common ancestor of anguilliforms 

 and elopiforms or in parallel, in response to the same selective 

 influence, after the adult eels had begun their divergence from 

 the still unspecialized elopiform fishes. The leptocephalus is 

 considered a specialized character by Forey (1973a), who sug- 

 gested that it arose before the elopid-albulid dichotomy. Trans- 

 forming elopoid leptocephali resemble transforming clupeiform 

 larvae (A/e^a/ops— Harrington, 1958: Plate 1; f/ops— Sato and 

 Yasuda, 1980: Fig. 1; ,4//)j//a-Hildebrand, 1963b: Fig. 23). 



The egg and larval evidence thus is consistent with a rela- 

 tionship between the Elopomorpha and the Clupeomorpha based 

 on primitive characters but is not helpful in aligning this Di- 

 vision (J. S. Nelson's usage, 1976) closer to any other. 



Summary and recommendations 



The eggs and early larval stages of the Clupeiformes provide 

 many taxonomic characters with potential value for testing phy- 

 logenetic hypotheses. Most of the discrete characters, such as 

 number of oil globules, have more than two states and the 

 continuous characters, such as degree of egg eccentricity, have 

 at least a moderate range of values. Although the fraction of 

 species whose eggs and larvae have been described is low and 

 the descriptions are uneven in quality and not distributed uni- 

 formly among taxa, egg and larval characters appear consistent 

 within genera. Within nominal subfamilies they are not consis- 

 tent, but the subfamilies show parallel trends in adult characters 

 and, in addition, the distribution of genera in higher taxa is not 

 yet agreed upon by all workers. 



Most descriptions of clupeiform larvae have been to enable 

 identification of regional species. Differences between larvae 

 usually involve subtle features of pigmentation or morphome- 

 try, or counts of meristic characters which converge with the 

 meristics of the adult. Phylogenetically significant characters 

 such as ephemeral dentition, osteological development, and the 

 comparative ontogeny of characters used in the taxonomy of 

 the adults are rarely mentioned. 



Future descriptions of eggs and larvae should address system- 

 atic characters as well as those needed for identification. Eggs 

 and larvae of many species should be redescribed to give com- 

 plete series through metamorphosis. Ontogenetic characters 

 should be used in revisions of the group. Classifications of the 

 Clupeiformes which are based on just a few characters should 

 be tested by comparing the ontogeny of those characters because 

 there are many apparently parallel trends in the group. Addi- 

 tional studies of the physiology and ecology of the eggs and 

 larvae should be done to determine the functional significance 

 of observed characters. It would also be useful to perform quan- 

 titative phenetic and cladistic analyses now of the Clupeiformes 

 for those regions or taxa for which information is already fairly 

 complete. 



National Marine Fisheries Service, Southeast Fisheries 

 Center, 75 Virginia Beach Drive, Miami, Florida 33149. 



Ostariophysi: Development and Relationships 



L. A. FUIMAN 



OSTARIOPHYSI, as regarded here, include all fishes whose 3 orders, about 55 families, and more than 5,000 species, there- 

 four or five anteriormost vertebrae are modified to form by accounting for over 70% of the world's freshwater fish species, 

 an otophysic connection, the Weberian apparatus (Rosen and Oslariophysans occupy most freshwater habitats worldwide, from 

 Greenwood, 1970). These primarily freshwater fishes comprise torrential Himalayan streams to still tropical lakes, as well as 



