Aceves-Medina et al.: Larval development of Symphurus williamsi from thie Gulf of California 



743 



vae we have seen (2.2 mm 

 BL). This fin is reabsorbed at 

 the postflexion stage (10.3 

 mm BL). Pelvic fins are de- 

 veloped at 5.7 mm BL. Only 

 in early juveniles is a blind- 

 side pelvic fin located on the 

 midventral line and the ocu- 

 lar pelvic fin is in a more dor- 

 sal position. 



Discussion 



Larvae of S. williamsi are 

 easily distinguishable from 

 those of S. atricaudus by dif- 

 ferences in pigmentation pat- 

 terns. During early preflex- 

 ion stage, S. williamsi has 

 two or three pigments over 

 the dorsal and midventral 

 lines, and the pigments over 

 the finfold are in the middle. 

 S. atricaudus has a series of 

 small melanophores along 

 the midventral line. The pig- 

 ments over the finfold are in 

 blotches and are on the ven- 

 tral and dorsal margins. There are also several pig- 

 ments over the ventral margin of the head and the 

 gut that S. williamsi does not have. 



At the flexion stage, S. williarrjsi has the spot pat- 

 tern along the dorsal and ventral profile. In contrast, 

 S. atricaudus has a series of melanophores along the 

 dorsal- and anal-fin margins and a series of pigments 

 along the midbody line that never develop in S. 

 williamsi. 



In S. williamsi. three elongated rays are charac- 

 teristic. In S. atricaudus, five rays appear first in 

 the dorsal fin but never become elongated. The in- 

 testine in S. williamsi projects only ventrally, 

 whereas in S. atricaudus the projection is ventro- 

 posterioriad. 



Larvae of S. williamsi can be distinguished from 

 those of S. elongatus by the pigmentation patterns. 

 In the preflexion stage, S. elongatus does not have 

 spots at the bases of the dorsal-fin rays, and these 

 larvae do not have pigments at the bases of each of 

 the anal- and dorsal-fin rays. Later in their develop- 

 ment, the pigmentation of S. elongatus consists of a 

 few distal pigments on the anal fin, twelve dashes 

 along the lateral midline, and a small blotch on the 

 caudal-fin rays, not observed in S. williamsi. In the 

 early transformation stage, S. elongatus has a series of 



Figure 2 



Symphurus wUliamsr. ( Al 10.0-mm postflexion larva; (B) 11.9-mm transformation larva. 



melanophores over the anterior part of the head, which 

 never appear in S. williamsi. Like S. atricaudus, S. 

 elongatus never develops elongated rays. 



Yevseyenko (1990) described Symphurus sp. lar- 

 vae. Its meristic characters have led us to believe it 

 is S. callopterus. principally because of its ID pat- 

 tern. These larvae are different from those of S. 

 williamsi in pigmentation pattern because on the 

 caudal section of the body an accumulation of pig- 

 ment in the form of two oblique bands and two belts 

 are found. These pigments are approximately equi- 

 distant from one other and never are found in S. 

 willianisi. 



Instead of three elongated dorsal-fin rays, like S. 

 willia/nsi, Symphurus sp. have the first 7 dorsal-fin 

 rays elongated from 7.5 to 25.4 mm BL (Yevseyenco, 

 1990). The presence of elongated fin rays in 

 pleuronectiform larvae has phylogenetic interpreta- 

 tions only in bothids and appears to be apomorphic 

 within the order and this family (Hensley and 

 Ahlstrom, 1984). However the use of this character- 

 istic for phylogenetic interpretations in cynoglossids 

 does not allow proper comparisons because most lar- 

 vae remain unknown. 



Adults of S. williamsi (7.5 to 11.6 cm BL) are 

 smaller than those of S. atricauda (13 to 18 cm BL) 



