SUMIDA ET AL EARLY DEVELOPMENT OF SEVEN ELATFISHES 



the caudal group of vertebrae forming. A slightly 

 more advanced 5. 5-mm NL specimen has 14 oppos- 

 ing neural and haemal processes of caudal verte- 

 brae formed as well as the four anteriormost and 

 last two precaudal neural processes. A neural or 

 haemal process consists of two portions — a divided 

 basal portion that forms the neural or haemal arch 

 ending in the second portion as a terminal spine. 

 On the 5. 5-mm NL specimen, only the tips of the 

 neural spines of the caudal group are ossified. Of 

 the precaudal group, ossification first occurs in the 

 arched portion of the anterior four neural proces- 

 ses and on the tips only of the last two precaudal 

 neural spines. On a 5.8-mm NL specimen with the 

 first 7 and last 4 precaudal neural processes and 17 

 pairs of neural and haemal processes in the caudal 

 group ossifying, all of the neural processes except 

 those of the 7 anterior precaudal vertebrae were 

 ossifying initially from both ends, i.e., from the 

 distal tips of the neural spines and from the basal 

 portion of the neural arches, with ossification from 

 both ends proceeding medially (Figure 12A). In a 

 6.1-mm NL specimen all 13 precaudal neural pro- 

 cesses and 19 neural and haemal processes in the 

 caudal group are ossified (Figure 12B). A 7.0-mm 



NL late flexion specimen has all neural and 

 haemal processes ossified except those on the ter- 

 minal preural vertebra, but no centra are ossified. 

 A 6.9-mm NL specimen, with all neural and 

 haemal processes ossifying, has various stages of 

 vertebral centra ossification with initial ossifica- 

 tion of centra occurring below the bases of the 

 neural and haemal arches and then filling in me- 

 dially; only the two vertebral centra adjacent to 

 the urostyle lack any ossification; the six verte- 

 brae immediately forward of these have the best 

 ossified centra. A 7.0-mm SL specimen has all 

 centra ossified. 



The bases of the dorsal and anal fins are present 

 on larvae as small as 5.3 mm NL and rays begin to 

 form by late flexion. Full complements of dorsal 

 and anal fin rays are present on most postflexion 

 specimens. Buds of the pelvic fins were first seen 

 on a 6.1-mm NL specimen, and the complete count 

 of six rays per fin is developed by 8.3 mm SL. 

 Pectoral rays form only toward the end of the 

 transformation stage after the left eye has nearly 

 completed its migration to the right side. 



Branchiostegal rays form progressively an- 

 teriorward during the period of caudal fin forma- 



FinURE 12.— Ossification pattern of the axial skeleton of Plcururuchrhys verticahs: A. 5.8 mm; B 6 1 mm 



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