SUMIDA ET AL EARLY DEVELOPMENT OF SEVEN FLATFISHES 



total vertebral counts which verified identifica- 

 tions and proved that Budd (1940) confused iden- 

 tifications of larvae of these two species. Radio- 

 graphs of transforming larvae, juveniles, and 

 adults of each species provided additional meristic 

 data. 



We divide the larval period into three stages, 

 preflexion, flexion, and postflexion, based on the 

 flexion of the notochord which occurs during 

 caudal fin formation (Moser and Ahlstrom 1970; 

 Ahlstrom et al. 1976; Moser et al. 1977). In 

 Pleuronichthys and some other flatfishes the initi- 

 ation of caudal fin formation begins while the 

 notochord is still straight, in the late preflexion 

 stage; we designate this phase as "early caudal 

 formation." We found it convenient to divide the 

 flexion stage into three substages, early flexion, 

 midflexion, and late flexion, dependent upon the 

 state of flexion of the notochord. In the early flex- 

 ion stage, the notochord is very slightly flexed 

 upward; in midflexion, it is flexed midway (nearly 

 a 45° angle); and in late flexion, the notochord is 

 approaching a terminal position, except that the 

 caudal rays remain in a slightly oblique position. 

 Transformation from the larval to juvenile stage 

 was marked by eye migration, development of os- 

 sified pectoral fin rays, scales, and the lateral line. 



MERISTIC COUNTS OF LARVAE 



Meristic counts overlap among species consid- 

 ered here, and for discrimination of species it is 

 necessary to use a combination of counts (Table 1). 

 Precaudal and caudal vertebral counts, used in 

 conjunction with dorsal and anal fin counts, are of 

 most use in relating larvae to juveniles or adults. 

 Pelvic fin ray counts are six per side in all seven 

 species and branchiostegal ray counts are seven 

 per side. Pectoral fin counts cannot be made on 

 larvae since ossified pectoral rays form at 

 metamorphosis. Gill rakers are not fully formed 

 during the larval period in the species described. 



DESCRIPTION OF EGGS 



Pleuronichthys spp. 



Eggs of three Pleuronichthys species were first 

 described by Budd (1940) who collected them in 

 plankton hauls from Monterey Bay, Calif. Budd 

 noted the hexagonal patterns on the chorions of 

 Pleuronichthys eggs. This type of ornamentation 

 of the egg shell is confined to Pleuronichthys 

 among flatfishes, but similar polygonal sculptur- 

 ing is found on eggs of the families Synodontidae 

 (Sanzo 1915; Mito 1961) and Callionymidae (Holt 

 1893; Ehrenbaum 1905; Mito 1962) and in a more 

 exaggerated form on eggs of the sternoptychid, 

 Maurolicus muelleri (Sanzo 1931; Mito 1961). and 

 the macrourid, Coelorhynchus coelorhynchus 

 (Sanzo 1933). Eggs of the three species of 

 Pleuronichthys described by Budd were strikingly 

 different in size; his largest, P. coenosus, averaged 

 1.88 mm in diameter, his intermediate-sized egg, 

 P. decurrens , 1.44 mm, and his smallest, P. ver- 

 ticalis, 1.07 mm. All had homogeneous yolk, and 

 lacked an oil globule. Our work shows that Budd 

 misidentified the two larger eggs and correspond- 

 ing larvae; the one he called P. coenosus is P. 

 decurrens and vice versa. Orton and Limbaugh 

 1 1953) described an egg with an hexagonal pattern 

 on its chorion that possessed a single oil globule; 

 they tentatively, but correctly, assigned it to P. 

 ritteri. White ( 1977) illustrated a developing egg of 

 P. ritteri from Newport Bay, Calif 



Information concerning egg diameters, pres- 

 ence or absence of an oil globule, and character of 

 the chorion are given in Table 2 for six of the seven 

 species treated in this paper. Egg diameters do not 

 change noticeably with the duration of preserva- 

 tion, although some shrinkage is known at the 

 initial time of preservation. There is no overlap in 

 egg size for the three species of Pleuronichthys 

 that lack an oil globule. Eggs of P. decurrens range 

 from 1.84 to 2.08 mm; those of P. coenosus, from 



Table l. — Meristics of the seven species of flatfishes in the eastern North Pacific that have heavily pigmented larvae.' 



'Menstics compiled in Table 1 are derived in partfrom literature, particularly Fitch (1963). Norman (1934), Townsend (1936). Clothier (1950). and Ginsburg 

 (1952), and m part from our onginal counts Where a range is given and one count is predominant, that count is italicized 

 ^Lower limb count only 



107 



