7723

• UCREFRP Catalog Number: 7723
• Author: Snyder, D. E. and R. T. Muth
• Title: Editor
• USFW Year: Series
• USFW - Doc Type: 1990
• Copyright Material: NO

Fig. 9. Position of mandibles relative to maxillae of
late metalarvae and only juveniles. Top - Xyrauchen
texanus and subgenus Catostomus; anterior ends of
mandibles far anterior to posterior ends of maxillae.
Bottom - subgenus Pantosteus; anterior ends of
mandibles slightly anterior to posterior ends of
maxillae.

of the mandibles positioned about midway
between anterior and posterior ends of the
maxillae.

Shape and size of anterior-dorsal projec-
tions on the maxillae are diagnostic for razor-
back sucker and subgenus Pantosteus greater
than 22 mm SL, sometimes smaller. The
anterior-dorsal projections of the maxillae are
very shallow to almost absent in razorback
sucker, relatively long and pointed (at least as
deep as wide at the base) in bluehead and
mountain suckers, and intermediate (promin-
ent but blunt and less deep than wide at the
base) in subgenus Catostomus (Fig. 10).

The angle at which the postcleithrum
extends from the cleithrum was initially sus-
pected to be diagnostic for subgenus Pantos-

teus, about 90" for bluehead and mountain
suckers and variable, but usually much less
for the others (Fig. 11). However, the differ-
ences in this character are not always distinct,
and perceived postc1eithral angle can be
affected strongly by angle of view. This
character needs further study.

Fig. 10. Anterior-dorsal maxillary projections of late
metalarvae and early juveniles. Top - Xyrauchen
texanus; very shallow to flat. Middle -- subgenus
Catostomus; short and blunt. Bottom -- subgenus
pantosteus; long and more pointed.

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