Larval development of the cutlips minnow, Exoglossum maxillingua, is briefly described from 90 specimens reared from eggs to identifiable juveniles. Total lengths (TL) of larvae ranged from 5.4 to 16.1 mm. Juveniles may be as small as 14.5 mm. During early larval development there is a brief increase in proportional measurements of head, eye, and predorsal lengths as compared to TL. This upward trend ends abruptly. The ratio of standard length to TL decreases sharply until the larva reaches approximately 15 mm TL. To separate E. maxillingua larvae in early developmental phases from larvae of commonly sympatric minnow species several characters can be used, including size, pigment pattern, number of preanal myomeres, and morphometry. After formation of the pelvic fin buds, the cutlips minnow larva is easily identified by the presence of a frenum, absent in other sympatric minnows, during the same developmental phase, except daces of the genus Rhinichthys. It differs from the daces in the position of its dorsal fin origin which is over the origin of the pelvic fin buds rather than behind it. The specialized lower jaw of Exoglossum develops primarily during the juvenile period.
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