Gill rakers begin to develop as elevations on the 

 dorsal surface of the ceratobranchial. They are 

 first seen when the larvae are about 8 mm. SL. 

 Four or five lower-limb gill rakers are first seen on 

 larvae about 9 mm. SL. They are short, blunt, well 

 separated, and located on the ceratobi-anchial. By 

 10.0 mm. SL the number of lower-limb gill rakers 

 has increased to seven and they are found on the 

 ceratobrancliials and hypobranchials. The adult 

 complement of 8 to 10 gill rakers on the lower limb 

 is reached at about 13.5 mm. SL. Gill rakers are 

 first seen on the epibranchial in 13.5 mm. SL 

 larvae, which have a single gill raker located im- 

 mediately above the angle. 



FIN FORMATION 



In the development of C. fmhriata the pectoral 

 fin is the first to appear and the last to complete 

 its development. The caudal fin completes develop- 

 ment first, followed in order by the dorsal, anal, 

 and pelvic fins. By about 8 mm. SL the adult 

 complement of fin rays is present in the caudal, 

 dorsal, and anal fins (fig. 2) . 



Pectoral Fin 



The pectoral fin is present on my smallest larva 

 (1.72 mm. SL) and is not fully developed on my 

 largest specimen (14.5 mm. SL). Initially it is 

 large and rayless. 



Caudal Fin 



The fully formed caudal fin has 17 principal fin 

 rays associated with the four hypural elements. 

 The dorsal and ventralmost caudal fin rays are 

 simple; the remaining rays are branched. Princi- 

 pal caudal fin rays are separable into two groups. 

 The nine upper rays are associated with the two 

 superior hypurals and the eight lower rays with 

 the two inferior hypurals (4-5 1 1 ). No caudal 

 fin rays are associated with neural and haemal 

 spines of the penultimate vertebra. A ventral 

 thickening near the posterior end of the notochord 

 is seen on specimens about 3.5 mm. SL. This thick- 

 ened tissue develops into the two median hypural 

 plates and their associated caudal fin rays. The first 

 four caudal fin rays to develop are seen first on a 

 5.44 mm. SL specimen and appear simultaneously 

 (fig. 2). They develop at an oblique angle to the 

 notochord and are divided into two groups, upper 

 and lower. This division separates the caudal fin 



into superior and inferior components. By about 

 8 mm. SL the notochord lias turned dorsally, the 

 hypurals and caudal fin rays are arranged parallel 

 to the axis of the body, and all principal caudal 

 fin rays are developed (fig. 2) , but the caudal oste- 

 ology is not fully developed until a larger size. 



Dorsal Fin 



Dorsal fin ray development is an important tax- 

 onomic character in larval flatfish. These fin rays 

 begin to develop in a thickened area above the 

 nape on specimens of about 2 mm. SL. My small- 

 est specimen with doi-sal fin rays (three elongate 

 rays) is 2.08 mm. SL (see app. table 1) . The origin 

 of the dorsal fin base moves anteriorly on the lar- 

 vae until the fin base is over the eye ; at this time 

 dorsal fin rays begin developing posterior to the 

 nape. All elongate dorsal fin rays develop first. 

 The origin of tlie dorsal fin continues to shift an- 

 teriorly until it becomes attached to the ethmoid 

 region of the cranium ahead of the eye. The first 

 three fin rays must develop simultaneously ; all but 

 three of the specimens between 2 and 3 mm. SL 

 have three or four fin rays (one with two, and two 

 with five). The number of fin rays on all but four 

 specimens between 3 and 5 mm. SL does not ex- 

 ceed 10 (one with 11 and three with 14), and most 

 of the rays are elongate. The number of fin rays 

 increases rapidly between 5 and 8 mm. SL; at 8 

 mm. SL the adult complement of 78 to 87 fin rays 

 is present (fig. 2) . Three of my 19 larval specimens 

 exceeding 8 mm. SL had 77 fin rays, and one had 

 76. 



Anal Fin 



Fifteen anal fin rays were present on a 5.9 mm. 

 SL specimen; none were discernible on smaller 

 specimens (fig. 2; app. table 1). Tlie number of 

 fin rays increased rapidly, as in the dorsal fin, and 

 the adult complement of 59 to 67 fin rays was de- 

 veloped by about 8 mm. SL (fig. 2). Four of 19 

 specimens exceeding 8 mm. SL had fin ray counts 

 of 58, three had fewer than 58, and the others had 

 counts between 59 and 67 (see app. table 1). 



Pelvic Fins 



Pelvic fin bases develop early. The left-side fin 

 base and its three elongate anterior fin rays de- 

 velop earlier than the right-side fin base. The left- 

 side fin base is first noted on specimens of about 



LARVAL BOTHID FLATFISH AND SPOTFIN FLOUNDER 



275 



