HOUDE, RICHARDS, and SAKSENA: EGGS AND LARVAE OF SCALED SARDINE 



ural centrum and was not connected to the first 

 uroneural base. 



In the 14.9-mm specimen major features in- 

 cluded an ossified area on the notochord posterior 

 to the sixth hypural (Figure 6D). This structure 

 apparently was temporary; it was not the third 

 uroneural and it was not as clearly observed 

 in larger specimens. Four upper secondary caudal 

 rays were visible though only the posteriormost 

 was stained. Three lower secondary caudal rays 

 also were present with only the posteriormost 

 stained. Two epurals were barely discernible and 

 were not stained. The "hemal archlike" bone of 

 the parhypural changed shape and appeared as 

 a forked bone which received the spine of the 

 parhypural between its forks. This small hemal 

 archlike bone also supported the first hypural 

 and abutted the first preural centrum, the noto- 

 chord between the first preural centrum and the 

 first ural centrum, and the first ural centrum 

 itself. The third hypural abutted the second ural 

 centrum, and the remaining hypurals abutted 

 the notochord. At this stage, it was obvious 

 that the first uroneural was fused to the first 

 preural centrum. The second uroneural was free 

 and never fused with any bone. 



In the 15.6-mm specimen, seven upper secon- 

 dary caudal rays and four ventral secondary 

 caudal rays were stained. Two epurals were 

 visible but weakly stained. An anteriorly directed 

 flange or expansion had developed on the base 

 of the parhypural. Its supporting hemal arch 

 structure was distinct and not fused with the 

 flange. The neural arch on the first preural 

 vertebra was beginning to ossify. In the 16.6-mm 

 specimen, the third uroneural was visible, lying 

 lateral to the second uroneural. It was shaped 

 like the second uroneural but was much smaller 

 and appeared as a well ossified splintlike bone. 

 The ossified area above the sixth hypural that 

 was noted in the 14.9-mm specimen was not 

 present. Three epurals were visible but not ossi- 

 fied. The full complement of secondary caudal 

 rays was present — eight upper, seven lower. 



In the 18.0-mm specimen, several significant 

 changes were evident (Figure 6E). First, only 

 two epurals were present, and they were slightly 

 stained. This probably was the result of indi- 

 vidual variation since three were observed in the 

 16.6-mm specimen. The neural arch of the first 

 preural vertebra had developed an upward pro- 

 jecting spinelike process. This neural arch lay 



over the posterior dorsal surface of the first 

 preural centrum between the bases of the left 

 and right first uroneural. We did not verify 

 that the dorsal nerve passes through this arch; 

 thus this neural arch and spine of the first 

 preural vertebra could be some other bone. Fusion 

 had not taken place between the neural arch and 

 the first uroneural bases in this specimen. The 

 first hypural no longer touched the first preural 

 centrum, and a remnant of its hemal archlike 

 base remained between the vertebra and the 

 hypural. The first or anteriormost upper and lower 

 secondary caudal fin rays lay parallel to the 

 body axis rather than slightly vertical as in 

 smaller specimens. The third uroneural lay 

 immediately above and posterior to the second 

 uroneural. 



Little difference was noted between the 

 19.3-mm and the 18.0-mm specimen except for 

 the complete absence of the hemal archlike 

 support of the first hypural in the larger speci- 

 men (Figure 6F). Three epurals were present 

 but were still only faintly stained. Without doubt, 

 these were the last components of the caudal 

 fin to ossify. In this specimen, there were nine 

 upper and seven lower secondary caudal rays. 

 The second preural vertebra had the anomalous 

 condition of bearing two neural spines. 



All three uroneurals are paired and obviously 

 provide rigid support for the notochord as the 

 tail develops. As a result, the first and second 

 uroneurals are among the first tail bones to 

 ossify. The ossified first uroneural fuses to the 

 first preural centrum after the centrum becomes 

 ossified. The other uroneurals were not fused to 

 any bone in the Harengula we examined nor 

 were they fused to other bones in large larvae 

 of Opisthonema (Richards, Miller, and Houde, 

 1974). 



Dorsal and Anal Fins 



Ossification of dorsal fin rays was first ob- 

 served in the 11.9-mm specimen. Twelve rays in 

 the midregion of the developing fin were faintly 

 stained. Supporting pterygiophores for these 

 rays also were faintly stained. About eight un- 

 stained anal rays were visible, but no supporting 

 pterygiophores were seen. In the 12.4-mm speci- 

 men, 12 dorsal rays also were stained but these 

 were the last 12 rays of the fin. Supporting 

 pterygiophores for these rays also were stained. 



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