Busby and Ambrose: Development of larval and juvenile Odontopyxis trispinosa and Xemeretmus latifrons 



41 I 



unpigmented region. Flexion and postflexion larvae of 

 0. trispinosa possess a single patch of melanophores 

 on the anal fin ? X. latifrons have two. 



Notochord flexion of O. trispinosa begins at approxi- 

 mately 7 .Omm and is completed by 11.8 mm. The larg- 

 est planktonic specimens of 0. trispinosa collected were 

 17.7 mm. Settlement probably occurs at approximately 

 this size. Notochord flexion of X. latifrons begins at 

 approximately 8.5 mm and is completed by 11.0 mm. 

 The largest planktonic specimens of X. latifrons col- 

 lected were 22.0 mm. 



Xeneretmus latifrons larvae are deeper bodied than 

 0. trispinosa. Xeneretmus latifrons also has a wider 

 head than 0. trispinosa at all stages of development. 

 Single barbels are present at the corners of the mouth 

 at about 15.0 mm in 0. trispinosa and 18.0 mm in 

 X latifrons. A distinct heart-shaped occipital pit is 

 present in O. trispinosa after about 15.0 mm. Post- 

 flexion larvae of each taxon are also distinguishable 

 by adult meristic characters. 



Ossification of most skeletal elements in O. trispinosa 

 begins earlier and is completed at smaller sizes than 

 inX latifrons. Head spination inX latifrons is gener- 

 ally reduced and dermal plates are absent on the head 

 region. The caudal-fin ray complement in X. latifrons 

 (2+6+6+1) is notably different than in O. trispinosa 

 (3+6+6+0). Ossification of the pterygiophores support- 

 ing the dorsal and anal fins, and the hypural plate is 

 complete by 27.0mm in O. trispinosa, but was not evi- 

 dent in cleared-and-stained specimens of X latifrons 



examined in this study (up to 39.2mm). This indicates 

 that transformation from larval to juvenile stages in 

 X. latifrons occurs at much larger sizes than in O. 

 trispinosa. Ossification of dermal body plates occurs in 

 nearly identical sequence, but X latifrons has more 

 plates in the DL+MD, IL, and VL+MV series. Dermal 

 plate formation in X latifrons is complete at a slightly 

 smaller size than in O. trispinosa. 



The preceding descriptions eliminate the confusion 

 in the literature concerning these larvae which resulted 

 from previous misidentifications (page 463 of Matarese 

 et al. (1989) and Figures A, B, and D from Marliave 

 (1975) are larvae of O. trispinosa misidentified as 

 X latifrons; Figure C from Washington et al. (1984) is 

 X latifrons). 



Comparison of O. trispinosa and X. latifrons 

 larvae with other known larval agonids 



Presently, larvae of 12 of 25 agonid taxa occurring in 

 the northeastern Pacific Ocean can be identified based 

 on single illustrations or complete developmental de- 

 scriptions. Of these 12 taxa, only O. trispinosa and X 

 latifrons described here are complete, illustrated at all 

 stages of development and include discussions of ossi- 

 fication sequence. 



By using body morphology, pigmentation, and mer- 

 istic characters, larvae of O. trispinosa andX. latifrons 

 are distinguishable from other northeastern Pacific 



