EARLY DEVELOPMENT OF THE TEN-POUNDER 



623 



STUDY MATERIAL 



The dates and locations of capture (fig. 1), and 

 numbers and size ranges for all leptocephali from 

 plankton collections follow : 



May 5, 1953, 31°57' N., 79°18' W. (1 specimen, 28.0 

 mm.) ; Oct. 12, 1953, 26°58' N, 79°40' W. (2 specimens, 

 11.2 and 11.7 mm.) ; Oct. 12, 1953, 27°40' N, 80°04' W. 

 (4 specimens, 15.2 to 22.4 mm.) ; Oct. 12, 1953, 27°37' N., 

 79°40' W. (1 specimen, 5.1 mm.) ; Oct 13, 1953, 28°00' N., 

 79°00' W. (1 specimen, 20.5 mm.) ; Oct. 15, 1953, 30°19' 

 N., 79°50' W. (1 specimen, 17.3 mm.) ; Oct. 16, 1953, 

 30°20' N., 79°26' W. (1 specimen, 5.3 mm.) ; Oct. 24, 1953, 

 31°34' N., 79°28' W. (1 specimen, 14.3 mm.) ; Nov. 12, 

 1953, 34°53' N., 76°10' W. (1 specimen, 31.3 mm.) 



Table 14 presents the dates and locations of cap- 

 ture for metamorphic larvae, juveniles, and adult. 

 Beach seining was done on St. Simons Island, Ga. ; 

 and marsh seining was done at Sapelo Marsh, 

 Mcintosh County, Ga. (an estuarine area behind 

 the barrier islands), and estuarine marshes near 

 Brunswick, Glynn County, Ga. 



MEASUREMENTS AND MERISTIC VALUES 



Table 1 gives selected measurements and 

 meristic values for all of the leptocephali (14) 

 from plankton collections; and the 11 early meta- 

 morphic larvae, juvenile, and adult which are 

 figured and described. Table 10 gives selected 

 measurements for all specimens, and includes 

 those from which regression lines were derived. 



DEVELOPMENT AND GROWTH 



The development and growth of body parts is 

 traced from the leptocephalus to the juvenile or 

 adult for each part separately, rather than in a 

 simultaneous treatment of all parts for each 

 period. 



MYOMERES 



The smallest leptocephalus I have ascribed to 

 E. saurus is 5.3 mm. standard length (fig. 2). It 

 has about 78 myomeres ( the last few in the caudal 

 region are indistinct), which precludes its being 

 either Tarpon or Albvla, both of which have fewer 

 than 72. Except for the monotypic genus Cyerna, 

 of the family Cyem.idae, I have been unable to find 

 reference to eel leptocephali having fewer than 100 

 myomeres. Cyerna atrum Giinther has 73 myo- 

 meres, and the larva ascribed to this genus, Lepto- 

 cephalus cyematis atri, has 75-77 myomeres ( Fish 

 1927). According to Berg (1947), Cyerna is 



499662 O— 59— —2 



"widely distributed, deepwater," and has 75-79 

 vertebrae. Bertin (1937, p. 5) gives a myomere 

 count of 74 (41 are preanal) for a damaged 

 11.2-mm. specimen of Cyerna. He figures a 

 20-mm. Cyerna leptocephalus which has 74 myo- 

 meres, 40 of which are preanal, and a body which 

 is much deeper than the head. My 5.3-mm. lepto- 

 cephalus has 70 preanal myomeres, and the head 

 is deeper than the body. These differences rule 

 out the genus Cyerna. There remains the possibil- 

 ity that some fish other than these has an unde- 

 scribed leptocephalid development to which the 

 specimen may be ascribed. 



Table 2 shows the number of myomeres for 

 specimens of different sizes and stages of develop- 

 ment. During the leptocephalus, and early and 

 mid-metamorphic periods the body is translucent 

 and thin, so that with transmitted light, the myo- 

 meres are visible. However, the myomeres in the 

 caudal region are not always distinct, and the 

 range shown (72-82) might reflect indefinite 

 counts. During the first part of the late meta- 

 morphic period the body becomes opaque, and 

 myomeres are indistinct. About 83 percent of the 

 specimens on which counts were made had 78-81 

 myomeres. 



FIN FORMATION 



Dorsal and anal. — The rudimentary anterior 

 rays in the dorsal and anal fins of some soft- rayed 

 fishes are disregarded by some authors when ray 

 counts are given, possibly because they are variable 

 in number or difficult to discern without dissection. 

 Instead of the total number of rays, their counts 

 include only the branched rays plus one un- 

 branched ray. In larvae I examined, in which 

 rays were forming or branching, all were discern- 

 ible without dissection. On some specimens ex- 

 ceeding 50 mm. in standard length it was necessary 

 to scrape away tissue covering the small anterior 

 dorsal and anal rays before they could be seen, but 

 on others all rays were discernible without dissec- 

 tion. My counts include the small rudimentary 

 rays. 



On the smallest leptocephalus, 5.3 mm. (fig. 2), 

 a median finfold begins immediately back of the 

 head, continues posteriorly, around the tip of the 

 urostyle, and forward ventrally to the anus. It 

 is swollen or bullate throughout most of its length, 

 and the margin is frayed or ruffled. A median 



