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<br />Table 2. Comparison of the more diagnostic differences in meristics for larvae and early juveniles of Upper
<br />Colorado River Basin catostomids. Character range is followed by the mean or more typical range. See Fig. 4 for
<br />methods of counting myomeres and fm rays. PV = posterior margin of the vent. Vertebra counts include four for
<br />the Weberian complex; dorsal fin ray counts are of principal rays; scale counts are of the lateral line or series. Data
<br />previously published by other authors (cited in species accounts) are given in parentheses.
<br />
<br />Character Catostomus Catostomus Catostomus Catostomus Catostomus Catostomus Xyrauchen
<br /> ardens catostomus commersoni discobolus latipinnis platyrhynchus texanus
<br />Myomeres to PV
<br />Proto- & meso larvae: 35-38,36-37 36-39, 37-38 34-40, 37-38 37-40,39 37-40,39 34-37, 36 37-41,38-39
<br />Metalarvae: 34-37,36 34-38,36 34-37,35 35-38,37 36-38,37 32-36,35 36-39,37
<br />All larvae: 34-38,36-37 34-39, 36-38 34-40, 35-38 35-40,37-39 36-40,37-39 32-37,35-36 36-41,37-39
<br />Myomeres, total
<br />Proto- & meso larvae: 45-48,46 45-49,47 43-49,46-47 47-49,48 47-49,48 43-47, 45-46 46-49,47-48
<br />Metalarvae: 43-47,45 44-48, 46 44-47,45 47-48,47 46-48,47 43-45,45 44-48, 46
<br />All larvae: 43-48, 45-46 44-49,46-47 43-49,45-47 47-49,47-48 46-49,47-48 43-47,45-46 44-49,46-48
<br />Vertebrae: 47-48 46-47 45-48, 46 47-49 47-50 46-50,46-48 45-47,46
<br /> (45-48,45-47) (44-48) (45-50,47-49) (42-48,44-47)
<br />Dorsal fin rays: 10-14,11-13 9-1], ]0 10-13,11-12 9-12,1] 11-14, ]2-13 9-11,10 12-16,14-15
<br /> (11-13) (9-12,10) (9-15, 10-13) (9-12,10-11) (l0-15,12-13) (8-13,10) (12-16,14-15)
<br />Lateral line scales: 57 -68, 62-68 103-116,105 56-72, 59-68 76-86
<br /> (54-79,60-70) (85-120,95-115) (53-85, 56-76) (78-122,86-115) (89-120,98-105) (60-108,75-97) (68-95,76-87)
<br />
<br />counts, especially at the lower end, is due to the far greater number of specimens examined for
<br />myomere counts (vertebra counts are based on only a few to several observations per species)
<br />and the difficulty in observing fIrst and last myomeres in some specimens, especially metalarvae
<br />for which polarizing fIlters are no longer useful. Probably for the latter reason, both total and to-
<br />the-vent myomere counts for metalarvae tend to range one or two myomeres less than for
<br />protolarvae and mesolarvae. A slightly more anterior vent position in metalarvae (and juveniles)
<br />than in earlier larvae might also account for some of the difference in myomere counts to the
<br />posterior margin of the vent (preanal myomere counts). Combined total vertebrae and myomere
<br />counts are greatest for bluehead and flannelmouth suckers (typically 47 or greater) and least for
<br />Utah, longnose, white, and mountain suckers (typically 47 or less); razorback sucker larvae
<br />typically have 46 to 48 total vertebrae or myomeres. The number of myomeres to the vent is
<br />typically 37 or greater for bluehead, flannelmouth, and razorback sucker and 36 or fewer for
<br />mountain sucker; typical ranges for Utah, white, and longnose suckers are intermediate and
<br />overlap with 35 or 36 to 37 or 38 myomeres to the vent. Unfortunately, the full ranges of
<br />myomere counts for these species generally overlap to a greater degree, making myomere counts
<br />less useful for diagnostic purposes.
<br />For proto larvae and flexion meso larvae most diagnostically useful measures relate to the
<br />amount of yolk remaining as the fIsh grow (Table 3). By the end of the proto larva phase,
<br />longnose, mountain and razorback suckers consume most or all of their yolk. White and Utah
<br />suckers also consume most but not all of their yolk, whereas bluehead and especially
<br />flannelmouth suckers still retain about half of their original yolk supply by the end of the
<br />proto larva phase. All suckers except flannelmouth complete yolk absorption by the end of the
<br />flexion meso larva phase.
<br />For late postflexion mesolarvae, metalarvae, and juveniles most diagnostic measures
<br />relate to the size and position ofthe dorsal fIn. The length of the dorsal fIn (from origin of the
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