RICHARDS, MILLER, and HOUDE: DEVELOPMENT OF THREAD HERRING 



Figure 7. — Opisthonema oglinum juvenile 24.4 mm standard length. 



were produced (Figure 7). Only about three or 

 four more rays were added, from 20 mm, until 

 the adult complement of 21 to 25 anal rays was 

 reached at 30 mm and over (Table 1, Figure 8). 



The pectoral fin appeared as a small, fan-shaped 

 structure just behind the cleithral ring, but this 

 structure enlarged gradually (Figures 2 to 7). 

 [Within the fan, "ray areas" differentiated soon 

 thereafter, but these had no apparent relation 

 to where rays actually ossify.] Ossified rays first 

 appeared at about 17 mm (five rays; see Table 1) 

 and quickly increased to about 10 rays at 19 mm. 

 The rounded fan shape of the pectoral fin changed 

 into the pointed shape characteristic of adults 

 between 19 and 23 mm (Figure 7). At 21 mm, 

 specimens had about 13 or 14 rays, and the 

 adult complement of 15 to 17 rays was reached 

 at 23 to 25 mm. The sequence of ray ossifica- 

 tion was in a dorsal (uppermost) to ventral 

 (lowermost) direction. 



Ossified pelvic rays appeared earlier than the 

 pectoral rays. At about 13 mm, larvae had about 

 four rays (Table 1), and at about 15 mm they 

 had five or six (Figure 5). The number of rays 



seemed to remain static for about the next 5 mm 

 of growth (10 specimens in the 15 to 20 mm size 

 range), but rather suddenly two more rays ap- 

 peared at about 20 mm (Table 1, Figure 7). The 

 pelvic ray count held constant, though size in- 

 creased to 50 mm, but in adults a ninth ray is 

 added as a flattened, segmented ray closely 

 adnate to the second (formerly most lateral) ray 

 to produce nine total rays. In our larger (30 to 

 54 mm) specimens (Figure 8) the flattened first 

 ray does not appear to be present. If it is, the 

 ray is so tightly attached to the second ray that 

 the two seem to be a single unit. 



Cephalic Development 



No ossification of any bones appeared before 

 specimens reached about 10.0 mm. In larvae as 

 small as 4.1 mm TL, the cranial bulb, dentaries, 

 and hyoid bones were visible as cartilaginous 

 elements. At about 10.0 mm, the maxillaries 

 and dentaries were easily distinguished and 

 began to show slight ossification (by stain uptake). 

 The jawbones more-or-less steadily increased in 



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