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Fishery Bulletin 91(3), 1993 



the entire caudal finfold. Caudal pigmentation persists 

 throughout development. 



Osteology Although precursors of some bony struc- 

 tures such as dermal plates and fin rays are discernable 

 as early as 8.0 mm, actual ossification of skeletal ele- 

 ments in 0. trispinosa does not begin until approxi- 

 mately 12.0 mm. 



Cranium The parasphenoid and basioccipital bones 

 of the cranium begin to ossify at 11.7 mm. At 13.2 mm, 

 several bones, including the nasal, frontal, parietal, 

 parasphenoid, basioccipital, and exoccipital are com- 

 pletely ossified. The rostral plate, nasal, lateral eth- 

 moid, supraethmoid, vomer, exoccipital, lachrymal, and 

 remainder of the circumorbital series ossify by 14.8 mm. 

 The sphenotic, prootic, epiotic, tabular, and ptero- 

 sphenoid are ossified by 27.0 mm. 



Spines Numerous head spines are ossified at 

 12.6 mm including the nasal, supraocular, the large 

 bilobed parietal, coronal, pterotics, supracleithral, an- 

 terior preoperculars and posterior preoperculars 1 and 

 2. The tympanic, cleithral, opercular, fifth and sixth 

 superior infraorbital spines, and the third and fourth 

 posterior preopercular spines are also ossified at this 

 stage. The frontal spine forms by 13.8 mm but is not 

 visible in lateral view because it is small and located 

 behind the anterior margin of the supraocular spine. 

 The frontal spine becomes overgrown with bone and is 

 difficult to distinguish at 17.2 mm. Interopercular and 

 superior infraorbital spines 1 and 2 begin forming at 

 about 14.2 mm. The rostral and postocular spines and 

 the postocular and posttemporal plates ossify at 

 14.8 mm. Superior infraorbital spines 3 and 4 and in- 

 ferior infraorbital plates 1 and 2 are completely ossi- 

 fied at this size. The third inferior infraorbital and 

 sclerotic plates are ossified by 17.2 mm. All spines 

 described here are paired with the exception of the 

 rostral. 



Mandibular region The dentary, angular, and ar- 

 ticular bones of the lower jaw are the first to ossify in 

 postflexion larvae of 11.7 mm. At 12.6 mm, the pre- 

 maxilla and maxilla are ossified. 



Palatine region Palatine, quadrate, metapterygoid, 

 mesopterygoid, ectopterygoid, and symplectic bones are 

 ossified at 12.6 mm. 



Opercular region The preopercle, opercle, inter- 

 opercle, and subopercle are ossified by 12.6 mm. 



Hyoid region The basihyal, hypohyal, urohyal, 

 ceratohyal, epihyal, interhyal, glossohyal, and bran- 

 chiostegal rays are also ossified by 12.6 mm. The 

 hyomandibula is ossified by 27.0 mm. 



Branchial region The pharyngobranchial teeth are 

 the first structures to ossify by 11.7 mm. Ossification 

 of the pharyngobranchials occurs at about 17.2 mm. 

 The pharyngobranchials begin as four pieces of carti- 



lage that apparently fuse before ossification of the 

 pharyngobranchial teeth. This process, however, was 

 not observed. The epibranchials (n=A) and cerato- 

 branchials (n=5) also ossify by 17.2mm. The remain- 

 ing branchial support structures, including the 

 hypobranchials (n=3) and basibranchials (n=3), ossify 

 by 27.0 mm. 



Appendicular region The cleithrum, postcleithrum, 

 and coracoid are ossified by 12.6 mm. The pelvic-fin 

 spine and all pectoral-fin rays, with the exception of 

 the ventralmost, ossify by 12.8 mm. The two pelvic-fin 

 rays and the final (14th) pectoral-fin ray are ossified 

 by 13.2 mm. The supracleithrum ossifies at about 

 13.8 mm. At 14.8 mm, ossification of the posttemporal 

 is completed. Ossification of the basipterygium occurs 

 at 17.2 mm. The scapula and three radials supporting 

 the pectoral-fin rays are ossified by 27.0 mm. 



Median fins All dorsal- and anal-fin spines and 

 soft rays are ossified by 12.6mm (Table 4). Six supe- 

 rior principal rays and five inferior principal rays in 

 the caudal fin are ossified at this size (total=ll). One 

 inferior principal (12), and two superior procurrent rays 

 (13, 14) are ossified by 13.2 mm. By 17.2 mm one addi- 

 tional superior (15) procurrent caudal ray is formed 

 which completes the adult count (3+6+6+0=15). Ossifi- 

 cation of the epural, hypural plate, and pterygiophores 

 supporting the dorsal- and anal-fin rays is completed 

 by 27.0mm. 



Vertebral column Ossification of vertebral elements 

 progresses from anterior to posterior. Notochord flexion 

 begins at approximately 7.0 mm and is completed by 

 11.8 mm. All, except the posteriormost caudal verte- 

 bral centrum, are ossified by 12.6 mm. The urostyle 

 and the anteriormost neural and haemal spines are 

 also complete by 12.6 mm. All abdominal neural spines 

 are complete and three additional haemal spines form 

 anteriorly by 13.2 mm. All vertebral centra are ossified 

 by 13.8 mm and two additional haemal spines have 

 formed. By 14.2 mm, 22 additional haemal spines de- 

 velop. All neural spines are ossified by 14.8 mm and 

 haemal spines are complete at 15.4 mm. 



Dermal plates Precursors of the supra (SLP) and 

 infralateral (ILP) plates first appear as small singular 

 spines which are distinguishable at about 8.0 mm. Os- 

 sification, however, does not begin until approximately 

 12.0 mm and progresses from anterior to posterior. Bone 

 develops radially from the base of the spine to eventu- 

 ally form the juvenile/adult dermal plate. By 12.6 mm, 

 ossification of the SLP and ILP series is complete. The 

 dorsolateral and mid-dorsal (DLP+MDP) and the ven- 

 trolateral and mid-ventral ( VLP+MVP) plate series are 

 complete by 14.8mm. The lateral line (LLP) plate se- 

 ries begins to form at about 14.0 mm. Lateral line plates 

 are the only plates that begin development as bifur- 

 cate spines. Ossification of the LLP series is complete 



