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Vol. 42, NO. 1
<br /> Y
<br />?O
<br /> _
<br />Opwo
<br />
<br />
<br />'lien texanus; chore
<br />itorv vesicle, Di
<br />notochord, OC
<br />(pronephric
<br />ventral to t:
<br />nentary tract
<br />complete; si .
<br />apparent.
<br />5, 103 houl-
<br />n tail and pos:.
<br />)utward from
<br />formed; nasal
<br />ng to straights:.
<br />-ion, 117 hour.
<br />nding from
<br />ericardial cr
<br />-trium lying 1,1
<br />1 conus arte
<br />nyocardium
<br />eral (gill) a-,
<br />ithin eyes, b
<br />A regions. Yoi
<br />body axis. 13:
<br />conus arteric•
<br />afferents ? i
<br />aorta and int_
<br />e artery - ca;.
<br />ein anterior
<br />common care
<br />sinus venos?
<br />motile, some:
<br />rudiments,
<br />i anlagen api
<br />rad to aud;
<br />rned. Stomac. ii
<br />December 1982 MINCKLEY, GUSTAFSON: RAZORBACK SUCKER DEVELOPMENT 557
<br />;
<br />CdV
<br />VA 1 MM
<br />
<br />clearly visible. Myotomes discernible above
<br />yolk. Embryos flex once every 12 to 13 heart
<br />beats.
<br />Stage 26: pectoral fin buds, day 6, 125
<br />hours, 7.3 mm. Rudiments of pectoral fins
<br />protrude, slightly flattened dorso-ventrally.
<br />Head continuing to extend outward from
<br />yolk.
<br />Prolarval Development
<br />Stage 27: hatching, 131 hours, 7.3 mm
<br />(Fig. 4). Pectoral fin buds paddle shaped. Tail
<br />"- straightened and median fin fold developed
<br />anteriorly on dorsum. Head flexed 45 degrees
<br />relative to body axis. Proctodeum discernible;
<br />eye pigment increased. Embryos scarcely
<br />motile, flexing along bottom with no directed
<br />movements.
<br />Stage 28: 142 hours, 7.5 mm. Four gill
<br />arches visible; head remains at 45 degree
<br />- angle to body axis. Pectoral fin buds thin and
<br />broadly rounded; ventral fin fold appearing
<br />behind proctodeum.
<br />Stage 29: 144 hours, 7.5 mm. Lower jaw
<br />formed, not yet reaching level of eye; mouth
<br />oriface round. Head angle less than 45 de-
<br />grees relative to body axis.
<br />Stage 30: early prolarva, day 7, 162 hours,
<br />8.0 mm (Fig. 5). Head straightened. Lower
<br />jaw reaching midlevel of eye, not movable.
<br />Pectoral fin differentiated into muscular lobe
<br />and membrane, not movable. Ventral fin fold
<br />developed to most anterior extension, em-
<br />bryonic fin membrane (continuous median
<br />fin) complete. Opercular membranes form-
<br />ing. Optic pigmentation brown, granular, al-
<br />most complete; no other melanophores.
<br />Stage 31: middle prolarva, day 9, 238
<br />hours, 9.0 mm. Rudimentary gas bladder evi-
<br />dent. Lower jaw to anterior border of eye,
<br />movable; mouth rounded and terminal.
<br />Opercle covers anteriormost gill. Pectoral fin
<br />0.5 mm long, movable. Proctodeum yet
<br />CFf MM DFf PFb GA
<br />„'.
<br />VFf YS AT PC St
<br />rig. 4. rrolarva of razorback sucker, Xyrauchen texanus, at hatching; legend as in Figures 1 to 3 when applicable,
<br />and AT = alimentary tract, CFf = caudal fin-fold, DFf = dorsal fin-fold, GA = gill arches, PC = pericardial cav-
<br />itY, PFb = pectoral fin-bud, Pr = proctodeum, St = stomadeum, and VFf = ventral fin-fold.
<br />Fig. 3. Embryo of razorback sucker, Xyrauchen texanus, at initial circulation of blood; embryo extended and cho-
<br />rion not depicted. Legend as in Figures 1 and 2 when applicable, and ACV = anterior cardinal vein, At = atrium,
<br />CA = carotid artery, CCV = common cardinal vein (duct of Cuvier), CdV = caudal vein, Co = conus artriosus,
<br />DA = dorsal artery, FF = fin fold, My = myomeres, NP = nasal placode, P = pupil, PCV = posterior cardinal
<br />vein, SV = sinus venosus, VA = vitelline artery, Vt = ventricle, and VV = ventral vein.
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