NOTE De Forest and Busby Development of larval and early juvenile Apodichthys flavidus 



479 



posterior during the early- and mid-flexion stages. 

 At 17.0 mm, the vertebral centra are completely dif- 

 ferentiated but remain unossified. In juveniles, the 

 vertebral centra are completely ossified. 



Caudal skeleton In early flexion larvae, the noto- 

 chord begins to bend upward and the haemal spine 

 of the second preural centrum, the fused parhypural 

 plus first and second hypurals, and the third hypural 

 are present (Fig. 2A). Caudal skeleton elements begin 

 to ossify at this stage, beginning at the base of each. 

 Ventral elements that develop at mid-flexion are the 

 haemal spine of the third preural centrum and the 

 fourth hypural (Fig. 2B). Dorsally, epurals 1-3 and 

 neural spines of the second and third preural centra 

 form during this stage. Elements present in early- 

 flexion are now fully ossified. At the beginning of 

 late-flexion (about 17.0 mm), a fifth hypural and a 

 fourth epural are present but not ossified (Fig. 2C). 

 In the 19.2-mm late-flexion specimen examined, the 

 third and fourth epurals were fused and the first 

 epural was fused to the neural spine of the second 

 preural centrum (Fig. 2D). In postflexion larvae, the 

 distal margins of hypurals 3-5 are oriented verti- 

 cally and the first epural separates from the neural 

 spine of the second preural centra (Fig. 2E). All other 

 elements in the caudal skeleton have grown and are 

 fully ossified. In juveniles, the caudal fin has the 

 adult form and the final element, the uroneural, is 

 present just ventral to the second and fused third 

 and fourth epurals (Fig. 2F). A ventral caudal radial, 

 present from mid-flexion to postflexion (Figs. 2, C-E), 

 is absent in juveniles. 



Discussion 



Our description of A. flavidus development can 

 be used to distinguish larvae of this species from 

 co-occurring species of Pholis spp., Apodichthys, 

 Ulvicola, and Xererpes along the West Coast of the 

 United States. As with Ulvicola sanctaerosae, A. 

 flavidus does not have a preflexion stage and larvae 

 hatch at an advanced developmental state (Watson, 

 1996). Larval Pholis spp. differ from larval A. flavi- 

 dus by the presence of pelvic fins in the former and 

 by differences in pigmentation. The melanophores 

 along the dorsal surface of the gut in Pholis spp. are 

 more numerous (about 25 vs. about 18 in postflexion 

 larvae) and closer in spacing anteriorly (Matarese et 

 al., 1989), and Pholis spp. do not develop an internal 

 row of melanophores along the dorsal margin of the 

 notochord. Apodichthys flavidus develops a series 

 of internal melanophores along the entire length of 

 the notochord by the mid-flexion stage. Larvae of U. 

 sanctaerosae can be distinguished from A. flavidus by 

 pigmentation and by the number and persistence of 

 pectoral-fin rays in postflexion larvae and juveniles. 

 Larval U. sanctaerosae have fainter melanophores 

 that are more irregularly spaced along the dorsal 



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