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<br />yzed. When comparing morphometric char-
<br />acters, be aware that some characters, espec-
<br />ially depths and widths at OD and on, are
<br />affected by the amount of yolk in early larvae
<br />and by health or condition in later larvae and
<br />juveniles.
<br />
<br />The more useful meristics are counts of
<br />lateral line (or series) scales for juveniles in
<br />which scales are sufficiently formed; principal
<br />dorsal rm rays (and corresponding pterygio-
<br />phores) and vertebra for late postflexion
<br />mesolarvae, metalarvae, and juveniles; and
<br />myomeres, both total and to the posterior
<br />margin of the vent, for all larval phases
<br />(Table 2). White and Utah suckers usually
<br />have fewer than 75 lateral rows of scales
<br />while bluehead and flannelmouth suckers
<br />usually have over 85, and mountain and
<br />razorback suckers typically have counts
<br />between 75 and 85. Typical counts of princi-
<br />pal dorsal fin rays are highest for razorback
<br />sucker with 14-15, and lowest for mountain
<br />sucker with 10; the other species have typical
<br />counts within the 11-13 range. However,
<br />when considering observed extremes in these
<br />counts, three species have ranges that include
<br />the count of 14 and four species include the
<br />count of 10.
<br />
<br />As would be expected, vertebra counts
<br />(based on specimens cleared and stained for
<br />cartilage or bone) nearly match or fall within
<br />the range of total myomere counts (all larval
<br />phases combined). The one notable excep-
<br />tion, an upper extreme of 50 vertebrae for
<br />the mountain sucker is based on one verified
<br />observation over 48. The greater range in
<br />values for myomere counts, especially at the
<br />lower end, is due to the far greater number
<br />of specimens examined for myomere counts
<br />(vertebra counts are based on only a few to
<br />several observations per species) and the
<br />difficulty in observing first and last myomeres
<br />in some specimens, especially metalarvae for
<br />which polarizing fllters are no longer useful.
<br />Probably for the latter reason, both total and
<br />to-the-vent myomere counts for metalarvae
<br />tend to range one or two myomeres less than
<br />for protolarvae and mesolarvae. A slightly
<br />more anterior vent position in metalarvae
<br />(and juveniles) than in earlier larvae might
<br />also account for some of the difference in
<br />myomere counts to the posterior margin of
<br />the vent. Combined total vertebrae and myo-
<br />mere counts are greatest for bluehead and
<br />flannelmouth sucker (typically 47 or greater)
<br />and least for Utah, white, and mountain suc-
<br />ker (typically 47 or less); razorback sucker
<br />
<br />Table 2. Comparison of the more diagnostic differences in meristics for larvae and early juveniles of
<br />Upper Colorado River Basin catostomids. Character range is followed by the mean or more typical range.
<br />See Fig. 4 for methods of counting myomeres and fin rays. PV = posterior margin of the vent. Vertebra
<br />counts include four for the Weberian complex; dorsal fm ray counts are of principal rays; scale counts are
<br />of the lateral line or series. Data previously published by other authors is given in parentheses.
<br /> Catostomus Catostomus Catostomus Catostomus Catostomus Xyrauchen
<br />Character ardens commersoni discobolus latipinnis platyrhynchus texanus
<br />Myomeres to PV
<br />Proto- and
<br />mesolarvae: 35-38, 36-37 34-40, 37-38 37-40, 39 37-40, 39 34-37, 36 37-41,38-39
<br />Metalarvae: 34-37, 36 34-37, 35 35-38, 37 36-38, 37 32-36, 35 36-39, 37
<br />All larvae: 34-38, 36-37 34-40, 35-38 35-40, 37-39 3640,37-39 32-37,35-36 36-41, 37-39
<br />Myomeres, total
<br />Proto- and
<br />mesolarvae: 45-48, 46 43-49,46-47 47-49, 48 47-49, 48 43-47, 45-46 46-49, 47-48
<br />Metalarvae: 43-47, 45 44-47, 45 47-48, 47 46-48, 47 43-45, 45 44-48, 46
<br />All larvae: 43-48, 45-46 43-49, 45-47 47-49, 47-48 46-49,47-48 43-47,45-46 44-49, 46-48
<br />Vertebrae: 47-48 45-48, 46 47-49 47-50 46-50, 46-48 45-47, 46
<br /> (44-48) (45-50,47-49) (42-48,44-47)
<br />Dorsal fin rays: 10-14, 11-13 10-13, 11-12 9-12, 11 11-14, 12-13 9-11, 10 12-16, 14-15
<br /> (11-13) (9-15, 10-13) (9-12, 10-11) (10-15, 12-13) (8-13, 10) (12-16,14-15)
<br />Lateral line
<br />scales: 57-68, 62-68 56-72, 59-68 76-86
<br /> (54-79,60-70) (53-85,56-76) (78-122,86-115) (89-120,98-105) (60-108,75-97) (68-95,76-87)
<br /> 25
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