RICHARDSON and JOSEPH: LARVAE AND YOUNG OF BOTHIDS 



of the head, the anterior part of the fin is de- 

 flected to the blind side. 



The anal fin forms similarly to the dorsal fin. 

 Rays become ossified centrally first, with forma- 

 tion progressing both anteriorly and poster- 

 iorly. Ossified fin rays are evident by 5 mm in 

 E. microstomus and 6 mm in C. arctifrons. 

 The full complement of rays is achieved by 

 8 mm in E. microstomus and 10 mm in C. 

 arctifrons. 



Pelvic fin buds appear at 5 mm in both 

 species. Ossification of fin rays begins from 5 

 to 6 mm in E. microstomus and at 6 mm in C. 

 arctifro)ts. The right pelvic fin completes forma- 

 tion before the left fin. The full complement 

 of six rays is consistently attained by 11-12 mm 

 in E. microstomus and 12-1- mm in C. arctifrons 

 (Table 6). By about 8 mm in E. microstomus 

 and 10 mm in C. arctifrons, the right pelvic 

 fin base is located noticeably above the body 

 midline on the blind side. Its origin is slightly 

 anterior to that of the left pelvic fin base which 

 is located on the body midline. These relative 

 positions of pelvic fin bases become more ob- 

 vious after the basipterygium ossifies (12 mm 

 in E. microstomus, later in C. arctifro)is) and 

 are difficult to detect on unstained specimens 

 until a larger size. 



With metamorphosis, the larval pectoral 

 fins transform to much smaller fins in relation 

 to body size, as incipient fin rays form. The 

 size at which pectoral fins are completely 

 formed could not be determined because of a 

 lack of specimens in the size range between 

 those undergoing metamorphosis and juveniles 

 of 20 -I- mm. 



Vertebral Column and Median 

 Fin Supports 



ossifies before the several centra immediately 

 preceding it. The abdominal rod, which extends 

 from the anteromost hemal spine to the position 

 of the anus and supports the interhemal spines 

 ventral to the gut cavity, begins to ossify before 

 the elements of the hypural plate and after 

 most centra are ossified. Ribs become evident 

 on abdominal centra about the time the abdom- 

 inal rod begins to ossify (7 mm for E. microsto- 

 mas and 8-9 mm for C. arctifrons). Interneural 

 and interhemal spines probably ossify near the 

 completion of metamorphosis. 



C. arctifrons generally lags behind E. micro- 

 stomus in development (Table 6). Neural and 

 hemal spines appear by 4 mm in E. microsto- 

 mus and 5 mm in C. arctifrons. Centra may 

 begin to ossify at 5 mm in E. microstomus and 

 6-7 mm in C. arctifrons. The adult vertebral 

 complement, including neural and hemal spines 

 and abdominal and caudal centra, is achieved 

 by 9 mm in E. microstomus. Neural and hemal 

 spines are all ossified by 9 mm in C. arctifrons, 

 but not all centra are consistently stained until 

 about 10 mm. 



Structure of the vertebral column and dorsal, 

 anal, and caudal fin supports is essentially the 

 same in juveniles and adults of both species 

 (Leonard, 1971a, Figures 19-21). The anterior 

 interneural spines are inclined forward such 

 that the first interneural spine, which is bifur- 

 cated (sometimes trifurcated in C. arctifrons), 

 lies in a horizontal position. The abdominal 

 rod, the distal portion of which is bifurcated, 

 provides support for the 6-9 most anterior 

 interhemal spines. The 17 rays of the caudal 

 fin occur in a 4-5-4-4 sequence, supported 

 by four hypural elements. Neural and hemal 

 spines of the penultimate vertebra support no 

 caudal fin rays. 



Sequence of ossification of the vertebral 

 column is the same for both species. Neural 

 spines of the abdominal region ossify first, 

 followed by neural and hemal spines of the 

 caudal region. Development progresses pos- 

 teriorily (Leonard, 1971a, Figure 18). Verte- 

 bral centra then begin to ossify in the posterior 

 abdominal region with development progres- 

 sing anteriorly. Centra of the caudal region 

 ossify from anterior to posterior. The urostyle 



Pectoral and Pelvic Girdles 



The cleithrum (Leonard. 1971a, Figure 22) 

 is ossified in the smallest stained specimens 

 and observable as early as 2.3 mm in unstained 

 larvae. The supracleithrum appears early in 

 both species (Table 7). The posttemporal and 

 postcleithrum ossify next, appearing first in 

 E. microstomus. Ossification of the basiptery- 

 gium (Figure 9) seems to coincide with achieve- 



753 



