Ohascanopsetta (Kyle, 1913) ; and Cydopsetta 

 (Goode and Bean, 1896). Many bothid larvae in 

 the western North Atlantic have spines. These are 

 more frequently seen on the preopercular margin 

 than on the head or body. Most bothids have a 

 swim bladder during the larval stage. Those larvae 

 with a protracted larval stage retain the swim 

 bladder longest. The migrating eye moves over the 

 middorsal ridge anterior to the origin of the dorsal 

 fin or through the head between the dorsal fin and 

 the supraorbital bars of the cranium. 



Permanent characters include meristic counts, 

 relation of the origin of the pelvic fin bases to 

 each other and to the cleithrum, and the arrange- 

 ment of the caudal fin rays with respect to the 

 other caudal fin rays and the bones of the hypural 

 plate. Size at metamorphosis is important in dis- 

 tinguishing between genera. 



MERISTIC CHARACTERS 



The most important characters for identifica- 

 tion of bothid larvae are meristics. Myomeres, 

 which correspond in number to vertebrae, are the 

 first countable item to develop. Those near the 

 anterior and posterior portions of the body are 

 difficult to count in the early stage larvae. Abdom- 

 inal vertebrae usually number 10, but can be 11 

 {Chascanopsetta has 16 or 17). Caudal vertebrae 

 are much more variable, ranging from 23 to 42. 

 The vast majority of bothid larvae have between 



34 and 40 total vertebrae or myomeres. Dorsal and 

 anal fin ray numbers are also variable and overlap 

 widely between species of Bothidae. The adult 

 complements of dorsal and anal fin rays are dis- 

 tinguishable in larval O. fiTribriafa by about 8-mm. 

 SL (fig. 2). The rate of fin ray development and 

 the fin ray numbers at the various sizes may have 

 generic or specific value. Although much meristic 

 overlap is evident among species of bothids, sev- 

 eral species can be separated by meristic values. 



PELVIC FIN 



Pelvic fin characteristics helpful in determining 

 a genus or generic group are : the position of the 

 fin bases in relation to the median line, size of 

 larvae when the left fin base and rays first appear, 

 relation of the origins of the right and left side 

 fin bases to the cleithrum, and the number of 

 elongate fin rays. 



Four of the 13 genera of bothids in the western 

 North Atlantic {Parcdichthys, Ancylopsetta, Gas- 

 tropsetta, and Hippoglossina) have the left and 

 right side fin bases above the median line; all other 

 western North Atlantic bothid genera have the left 

 side fin base on the median line and the right side 

 fin base above the median line. 



I have only seen Parcdichthys of the four genera 

 with left and right side pelvic fin bases above the 

 median line. In Paralichthys the left side fin base 

 does not appear until the larvae are about 7 mm. 



u. so 



o 



i <o 



DORSAL-O 

 ANAL-X 

 CAUDAL - it 



O O O O 



o<b 



X X '^ 



OOO « ° 



o * 



** * ***♦ • * 



***** 



II 13 13 



STANDARD LENGTH (MM.) 



FiGDBE 2. — Relation of number of dorsal, anal, and caudal fin rays to standard len^h of 



Cydopsetta fimhriata larvae. 



266 



U.S. FISH AND WILDLIFE SERVICE 



