— SOii 



Figure 6. — Exterior view of left maxillary bone of a 

 22-innn. (fork length) Atlantic menhaden lai-va 

 showing the single row of teeth; posterior end on 

 left. 



Figure 8. — First left gill arch of a 20-mm. (fork 

 length) Atlantic menhaden larva showing the rudi- 

 mentary rakers on the upper and lower limbs. 



to 20 30 40 50 



lllllllllllwillllllllllNllllllllllMIIIIIIIIIIIII 



Figure 7. — Top interior view of dentary bones of a 

 22-mm. (fork length) Atlantic menhaden larva 

 showing the single row of teeth (1 division=50 n). 



superfluous for ingesting the smaller orga- 

 nisms that compose the phytoplankton; denti- 

 tion becomes nonfunctional after metamor- 

 phosis. 



Gill Rakers and Accessory Structures 



During metamorphosis the gill rakers in- 

 crease in length, number, and complexity. In 

 larvae under 25 mm. long the lower limb (con- 

 sisting of the hypobranchial and the cerato- 

 branchial segments) and the upper limb (epi- 

 branchial segment) are slightly curved. Rakers 

 initially form as rounded protuberances at the 

 angle between the upper and lower limbs (fig. 

 8) ; those of the lower limb appear first. Two 



rows of barbs appear along the longitudinal 

 axis of individual rakers. As fish increase in 

 length, the rakers become distinctly elongate. 

 Barbs increase in number, become slightly 

 curved, and ultimately develop a serrate tip 

 (fig. 9) . The hypobranchial segment of the first 

 gill arch becomes more cui"ved anteriorly; 

 rakers continue to form at the anterior ends 

 of the epibranchial and hypobranchial seg- 

 ments, while those near the angle on the upper 



Figure 9. — Photomicrograph showing the barbs on the 

 rakers of the first left gill arch of a 32-mm. (fork 

 length) Atlantic menhaden prejuvenile (1 division = 



50 m). 



FOOD OF YOUNG ATLANTIC MENHADEN IN RELATION TO METAMORPHOSIS 



501 



