MOSER: DEVELOPMENT OF ROCKFISH 



Table 4. — Sequence of initial ossification of branchial 

 arch elements in larvae of Sebastes macdonaldi. 



Table 5. — Sequence of initial ossification of head spines 

 of larvae of Sebastes macdonaldi. 



on the ultimate preterminal vertebra, is present 

 in a 15.0-mm stained specimen. 



The next elements of the axial skeleton to ap- 

 pear are the vertebral centra. The most anterior 

 centra begin to ossify in larvae about 7.2 mm 

 long. Ossification within each centrum begins 

 at the bases of the neural arch and spreads me- 

 sially to form a straplike bridge between the 

 bases. A similar structure forms ventrally be- 

 tween the bases of the haemal arch and ultimate- 

 ly the two bridges are joined by lateral ossifica- 

 tion, to produce a complete central ring. This 

 process proceeds in a posteriad sequence until 

 the full complement of 25 central rings is at- 

 tained in larvae of about 10.0 mm. Ossification 

 of the ural centrum begins in an 8.2-mm speci- 

 men with the formation of two tandem osseus 

 plates on each lateral surface. These spread 

 rapidly to cover the entire lateral and dorsal 

 surface of the centrum. Ossification of two 

 ventral unossified regions is completed at about 

 10.0 mm to coincide with the formation of the 

 ultimate preterminal centrum. 



Haemal arches begin to ossify at about 8.2-mm 

 length in a manner similar to that of the neural 

 arches. Closure of the haemal processes into 

 arches and the formation of haemal spines pro- 

 ceeds posteriad sequentially; when completed at 

 10.0 mm, vertebrae 1 to 4 are without haemal 



Spine 



Element 



Size of specimen 



at 



initial appearance 



(mm) 



Pterotic 



Preopercular, 3rd, posterior series 



Preopercular, 4th, posterior series 



Parietal 



Postocular 



Preopercular, 1st, anterior series 



Preopercular, 2nd, anterior series 



Preopercular, 3rd, anterior series 



Preopercular, 2nd, posterior series 



Supracleithral 



Suborbital, 1st, inferior series 



Suborbital, 1st, superior series 



Preopercular, 1st, posterior series 



Nuchal 



Opercular, 1st 



Opercular, 2nd 



Preopercular, 5th, posterior series 



Suborbital, 3rd, superior series 



Cleithral 



Nasal 



Suborbital, 2nd, inferior series 



Suborbital, 2nd, superior series 



Preocular 



Supraocular 



Tympanic 



processes, 5 to 9 have unfused haemal processes, 

 10 and 11 have haemal arches without spines, 

 and 12 to 25 have arches and spines. 



All of the remaining major axial elements be- 

 gin to ossify in larvae 10.0 mm or longer. The 

 uroneurals appear as a pair of slender elements 

 above the terminal centrum in a 10.0-mm speci- 

 men; they remain paired and sliverlike through- 

 out the larval period. The proximal radial ele- 

 ments of the dorsal fin also begin to ossify at 10.0 

 mm and those of the anal fin at 12,0 mm, both 

 in a posteriad direction; neither series is com- 

 pleted by 15.9 mm. A single interneural appears 

 slightly above and in advance of the first neural 

 spine in a 15.0-mm larva. Also, in this specimen 

 the most anterior few ribs have just begun to 

 ossify. 



Several generalizations can be made from the 

 information listed in Table 3. It is obvious that 

 the various skeletal elements begin to ossify over 

 a wide range of larval sizes and that the elements 

 vary greatly in the time required for each to 

 attain its adult form. For example, in the neuro- 

 cranium, the jugal (third circumorbital) is 

 formed over a span of nearly 7.0-mm length 

 (8.2-15.0 mm) while the vomer begins to ossify 



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