RICHARDSON and JOSEPH: LARVAE AND YOUNG OF BOTHIDS 



Upper and Lower Jaws 



By 4 mm, parts of the premaxillary, maxil- 

 lary, dentary, and articular have begun to ossify 

 in both species (Table 7). Development of the 

 upper jaw (Leonard, 1971a, Figure 23) is 

 similar to that described for other highly 

 evolved forms of fishes (Berry, 1964). The 

 toothless maxillary ossifies to a greater degree 

 than the premaxillary in early stages and is 

 included in the gape. As development proceeds, 

 the premaxillary continues to grow posteriad 

 and eventually eliminates the maxillary from 

 the gape in C. arctifrois and nearly so in E. 

 microstomus (Figures 9-11). Ossification of 

 the jaw bones appears to be more advanced in 

 C. arctifrons than in E. microstomus of equal 

 size. This tendency is evident in the dentary 

 and articular in C. arctifro^is larvae of 4 mm. 

 The angular process on the articular appears 

 first in C. arctifrons (about 7 mm) and later 

 (about 8 mm) in E. microstomus. 



The fact that C. arctifrons has a larger jaw 

 becomes evident by about 7 mm. The maxillary 

 and premaxillary are longer than in E. micro- 

 stomus and the processes of the dentary extend 

 farther posteriorly. The anteromost process 

 located laterally on the anterior knob of the 

 maxillary becomes noticeably more elongate 

 in C. arctifro)ts by about 12 mm (Figure 9). 

 This maxillary process forms the osseous pro- 

 tuberance of the snout characteristic of adults 

 (Figure 10). The premaxillary process, which 

 occurs medially in the upper jaw, appears 

 longer and narrower in C. arctifrons of about 

 12 mm, but not in juveniles and adults. 



Teeth, distributed evenly in single rows on 

 the left and right sides of the anterior portion 

 of the premaxillary and dentary, are evident 

 in the smallest stained larvae (in 3 mm un- 

 stained larvae) of both species. Teeth in adult 

 E. microstomus are distributed mainly on the 

 blind side (Figures 10, 11). This unequal dis- 

 tribution becomes apparent on the eyed side 

 during metamorphosis (Figures 9, 10) as larval 

 teeth are replaced. On the eyed side of juvenile 

 and adult E. microstomus, teeth are more 

 numerous on the lower jaw, e.g.: 



In juvenile and adult C. arctifrons, teeth on the 

 eyed side are more numerous on the upper 

 jaw, e.g.: 



Teeth on the blind side of the lower jaw are 

 about equal in number to those of the upper 

 jaw for each species. C arctifrons has a 

 greater total number of teeth corresponding to 

 its larger mouth. 



Oromandibuiar Region 



The ectopterygoid is the first bone to ossify 

 in this region, usually between 4 and 5 mm in 

 both species (Leonard, 1971a, Figure 24). 

 The quadrate, endopterygoid, hyomandibular, 

 and symplectic become ossified in that order 

 and at an earlier stage in E. microstomus than 

 C. arctifro)is (Table 7). By about 12 mm, de- 

 gree of ossification of bones in this region is 

 similar in both species (Figure 9). The palatine 

 and metapterygoid become ossified sometime 

 after metamorphosis (Figures 10, 11). 



Structure of bones in this region is similar 

 in the two species. The anterior wing of the 

 hyomandibular extends farther ventrally along 

 the central shaft of the bone in juvenile and 

 adult E. microstomus, particularly on the eyed 

 side. 



Opercular Series 



The opercle and preopercle are partly ossi- 

 fied in both species by 4 mm (Leonard, 1971a, 

 Figure 25). The interopercle and subopercle 

 ossify first in E. microstomus (Table 7) between 

 5 and 6 mm and by 7 mm in C. arctifrons. 



Within this series, a major structural differ- 

 ence exists between larvae of these two species. 

 Spines are present on the posterior preoper- 

 cular margin of E. microstomus by 4 mm. (They 

 may be seen on unstained larvae of 2.5 mm.) 

 With development, the number of spines in- 

 creases over the lateral surface of the pre- 

 opercle. They begin to disappear at around 

 8 mm and can no longer be seen by 10 mm. 

 C. arctifro)is has no preopercular spines. 



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