MOSER: DEVELOPMENT AND DISTRIBUTION OF SEBASTOLOBUS 



to 9 superior and 7 to 9 inferior procurrent rays 

 are present in 10-mm larvae of S. altivelis and the 

 full complements of 8 to 10 superior and inferior 

 elements are present in 12- to 13-mm larvae of S. 

 alascanus. 



The dorsal and anal fins begin to develop in 

 6-mm larvae of Sebastolobus and the full com- 

 plements of rays are ossifying in 7-mm larvae of 

 both species. In S. altivelis the usual number of 

 spinous dorsal rays is 15 and in S. alascanus the 

 usual number is 16. Both species have 8 to 10 soft 

 dorsal rays with a usual number of 9. 



Pigmentation 



The melanophore pattern of embryos and yolk- 

 sac larvae of Sebastolobus has been described by 

 Pearcy ( 1962 ). At the beginning of the larval stage 

 (3.5 mm) the melanophore pattern is distinctive. 

 Large median melanistic blotches oppose each 

 other about midway back on the tail (Figure lA, 



30 30 ' 



STANDARD LENGTH (mm) 



Figure 9. — Relationship of pectoral fin length to body length in 

 Sebastolobus. Symbols as in Figure 8. 



.,^' 



20 30 40 



STANDARD LENGTH Imml 



Figure 10. — Relationship of depth of pectoral fin base to body 

 length in Sebastolobus. Symbols as in Figure 8. 



B). In some specimens, the blotches are expanded 

 to form a band. Also, melanophores cover the dor- 

 solateral surfaces of the posterior region of the 

 gut. The melanistic tail blotches are transitory; 

 they are lost in some larvae as small as 4.2 mm 

 and one or both are absent in most larvae between 

 5.0 and 6.0 mm in length. The dorsal spot was 

 absent in all larvae larger than 6.0 mm and the 

 ventral spot was absent in all larger than 6.4 mm. 

 In contrast, the gut pigment is augmented 

 throughout the larval period, extending forward 

 to the axillary region and internally anterior to 

 the cleithrum in larvae about 5.0 mm long. When 

 the larvae reach 6.0 mm the pigment extends onto 

 the ventral surface of the gut and dorsally as 

 deeply embedded pigment at the nape. With con- 

 tinued development the melanophores form a 

 solid sheath on the peritoneum surrounding the 

 gut. 



Melanophores appear at the posterior margin of 

 each pectoral fin in some larvae as small as 4.0 

 mm. About half the larvae examined between 4.0 

 and 5.0 mm have this posterior margin of fine 

 melanophores and the pigment is present in all 

 larvae in the 5.0- to 11.0-mm range. The 

 melanophores are then lost, and almost all larvae 

 larger than 11.0 mm have pigmentless fins. 



Melanophores appear on the posterior lobes of 

 the brain in 5.2- to 7.0-mm larvae and are present 

 in all larvae larger than this. They also appear 

 above the anterior lobes of the brain in larvae 

 between 7.0 and 9.0 mm in length and in most 

 larvae larger than 9.0 mm. 



Juvenile pigmentation begins to appear in some 

 specimens of S. altivelis of the 14- to 20-mm size 

 range. On the head, patches of melanophores ap- 

 pear on the opercle, cheek, snout, and jaws. In 

 most specimens larger than 22 mm, the patches 

 are confluent, and the head is generally dusky 

 with darker areas at the opercle and along the 

 upper jaw. 



A patch of melanophores appears superficially 

 over each side of the gut in specimens as small as 

 14 mm. These patches expand to form a solid 

 melanistic sheath in some specimens of the 14- to 

 20-mm size range. The posterior margin of the 

 sheath is an arc running from the vent to the nape 

 and stands out sharply against the pigmentless 

 region of the trunk posterior to the sheath. With 

 continued development the pigment sheath ex- 

 pands posteriad and is a striking feature of the 

 pelagic juveniles. In the 20- to 30-mm size range 

 the sheath extends posteriad to a vertical from the 



879 



