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



calcification as distinct cartilaginous structures. 

 Our four smallest specimens (4.8, 6.2, 6.5, and 

 8.9 mm) showed no evidence of staining and 

 only slight indication of developing bone struc- 

 tures. Our first specimen to show clear evidence 

 of stain uptake and well-formed cartilaginous 

 structures was 10.9 mm. The only bone which 

 was stained in this specimen was the cleithrum. 

 The next bones to stain (an 11.5-mm specimen) 

 were the maxillaries, dentaries, principal caudal 

 fin rays, hypurals, and parhypural. Ossification 

 then proceeded rapidly as larvae grew. 



The Caudal Fin Complex 



Clupeids have a complex caudal fin, and for 

 descriptive purposes we follow the terminology 

 of Nybelin (1963). The adult caudal fin has the 

 following structures: 2 ural vertebrae, 6 hy- 

 purals, a parhypural associated with the first 

 preural vertebra, 19 principal caudal rays (the 

 lower and upper are unbranched, the remainder 

 branched), 2 or 3 epurals, 3 pairs of uroneurals, 

 8 or 9 dorsal secondary caudal rays, 7 ventral 

 secondary caudal rays, and a modified neural 

 arch and spine on the first preural vertebra. 

 In a 9.9-mm specimen the parhypural and the 

 first four hypurals were visible (but not stained) 

 as distinct cartilage entities (Figure 6A). A notice- 

 able gap was present between the second and 

 third hypural which persisted to the adult stage 

 and separated the 9 lower from the 10 upper 

 principal caudal rays. 



The association of individual principal caudal 

 fin rays with the parhypural and hypurals was 

 nearly constant. Our method of counting princi- 

 pal caudal rays was anterior to posterior or, 

 after notochord flexion, ventral to dorsal. The 

 hjqjurals were counted similarly. The first two 

 principal rays articulated with the parhypural, 

 rays 3 to 7 articulated with the first hypural 

 (in specimens larger than 15.0 mm ray 8 also 

 associated with this hypural); rays 8 and 9 with 

 the second hypural; rays 10 to 14 with the 

 third hypural; rays 15 and 16 with the fourth 

 hypural; rays 17 and 18 with the fifth hypural; 

 and ray 19 with the sixth hypural. Rays 1 and 19 

 were stained deepest, and staining decreased 

 medially indicating that rays 9 and 10 were 

 the last to ossify although these rays were the 

 first to develop. 



In the 11.5-mm specimen (Figure 6B) there 



was a slight indication of ossification of the first 

 pair of uroneurals and the neural arch of the 

 first preural vertebra. The hypurals were all 

 stained as was the parhypural and hemal spine 

 of the second preural vertebra. In the 11.9-mm 

 specimen the first uroneural pair was well stained 

 as was the second uroneural pair, and the second 

 ural centrum was deeply stained. The second 

 uroneural lay just posterior to the second ural 

 vertebra along the plane of the notochord. The 

 first uroneural originated above an area that 

 became the first preural centrum, but there was 

 no indication of the centrum at 11.9 mm. The 

 first uroneural extended along the notochord 

 over the second ural centrum and ended midway 

 along the second uroneural. The second uroneural 

 extended from the second ural centrum to the 

 origin of the sixth hypural. Two other structures 

 were discernible but not stained at 11.9 mm — 

 the hemal spines of the second and third preural 

 vertebrae and the posteriormost ventral secon- 

 dary caudal fin ray. 



In the 12.0-mm specimen, little change oc- 

 curred. In the 12.4-mm specimen, all the struc- 

 tures mentioned above were more deeply stained, 

 and the neural and hemal spines of the second 

 preural vertebra (though this vertebra is undif- 

 ferentiated) were stained (Figure 6C). Of partic- 

 ular interest in this specimen was the marked 

 similarity of the hemal spine of the second 

 preural vertebra to the parhypural. Nybelin 

 (1963) considered the parh3TJural to be a hemal 

 spine, and our observation bears this out in as 

 much as the caudal artery goes through this bone 

 rather than over it. Monod (1968) has referred 

 to the hemal spine of the first preural centrum 

 as the parhypural bone and Hollister (1936) 

 considered this bone to be a hypural. We use the 

 term parhypural because it has characteristics 

 of both a hypural bone and a hemal spine. 

 During its development, it closely resembles a 

 hypural and in fact is joined to the first hypural 

 (see Figure 6D), and it bears two principal 

 caudal rays. Both spines of the two preural 

 vertebrae are flattened bones with developing 

 hemal arches between the spine base and the 

 notochord. In the 14.0-mm specimen, the first 

 preural centrum and the two ural centra were 

 stained as was the lower portion of the second 

 preural centrum. The posteriormost ventral 

 secondary caudal ray was stained. A neural arch 

 was visible, though unstained on the first pre- 



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