.
Dentaries with a few small, but distinct acicular
teeth; dorsal and lateral surfaces mottled with
large, well spaced melanophores, some loosely
arranged to form irregular blotches; Orinoco Basin.....Leptodoras
sp. 4 (aff. myersi)
10B. Dentaries edentulous (except in
small juveniles of some Amazon species); dorsal
and lateral surfaces not mottled.....11
11A. Distal half of dorsal fin with distinct
black spot or blotch.....Leptodoras hasemani
11B. No black spot or blotch on distal
half of dorsal fin.....12
12A. Dorsal spine thin and greatly extended
as a long flexible filament; predorsal distance
relatively short, 26–28% of SL; bases of
dorsal and paired fins with intense black pigment.....Leptodoras
juruensis
12B. Dorsal spine not greatly extended
as a long flexible filament (except in a few
rare instances); predorsal distance longer,
>=30% of SL; pigmentation on bases of dorsal
and paired fins variable.....13
13A. Broad dusky nuchal saddle extending
ventrally across tympanum and humeral process,
finishing on the lower side level with the pelvic-fin
origin.....Leptodoras myersi
13B. No dark nuchal saddle and bar on side
of body.....14
14A. Flap-like posterior extensions at
corners of lower lip narrow and long, finishing
beyond tips of similar extensions at corners
of upper lip; black melanophores concentrated
on basal portions of dorsal spine and usually
fin.....15
14B. Flap-like posterior extensions at corners
of lower lip relatively short, finishing even
with or before tips of similar extensions of
upper lip; base of dorsal fin without intense
black pigmentation (may appear dusky, but never
black).....16
15A. Anterior midlateral plates shallow,
height of 2nd midlateral plate less than or
equal to vertical diameter of eye; anterior
nuchal plate usually narrow, permitting suture
between supraoccipital and middle nuchal plate;
profile of snout weakly concave.....Leptodoras
praelongus
15B. Anterior midlateral plates deeper,
height of 2nd midlateral plate distinctly greater
than vertical diameter of eye; anterior nuchal
plate usually expanded laterally and sutured
to epioccipital; profile of snout rounded (convex).....Leptodoras
copei
16A. Upper labial extension relatively
long with narrow base and expanded distal portion
that curves medially and has a distinctly pointed
or triangular-shaped tip; dorsolabial membrane
well-developed, widely rounded posteriorly;
humeral process relatively short, usually 19.3–28.5
times into SL…..17
16B. Upper labial extension (excluding
small fimbriae) with rounded or truncate distal
tip; dorsolabial membrane weakly to moderately
developed, evenly attenuate posteriorly; humeral
process longer, 13.9–19.2 times into SL…..19
17A. Adipose eye relatively large, horizontal
length 1.49–1.79 times into postorbital
distance and 23.1–27.8% of predorsal distance;
blackwaters of Negro Basin and Casiquiare…..Leptodoras
sp. 3 (Negro form)
17B. Adipose eye smaller, horizontal length
1.81–2.27 times into postorbital distance
and 18–23.2% of predorsal distance; white
to moderately blackwaters of Amazon Basin…..18
18A. Snout relatively long, length 1.06–1.22
times postorbital distance, 42.4–46.6%
of predorsal distance; sum of midlateral scutes
79–86 (modally 82)…..Leptodoras
sp. 3 (Nanay form)
18B. Snout shorter, length 0.85–1
times postorbital distance, 37.6–41.3%
of predorsal distance; sum of midlateral scutes
83–92 (modally 88)…..Leptodoras
sp. 3 (Amazon form)
19A. Adipose eye relatively large, horizontal
length 11.2–13.9 times into SL; predorsal
distance relatively long, 35.5–38.7% of
SL; thin low pre-adipose ridge always present…..20
19B. Adipose eye smaller, horizontal
length usually 14.5–20.6 times into SL;
predorsal distance somewhat shorter, 31.6–36.5%
of SL; preadipose ridge absent or only weakly
developed…..21
20A. Postorbital length 37.6–41.8%
of predorsal distance…..Leptodoras
linnelli
20B. Postorbital length 42.9–44.6% of predorsal
distance…..Leptodoras sp. 2 (Orinoco)
21B. Postorbital length 1.8–2.01
times distance from snout tip to anterior nares;
snout length 37.8–41.8% of predorsal distance;
anterior scutes comparatively shallow, covering
between 1/4 and 1/2 of corresponding body depth;
sum of midlateral scutes 82–86 (modally
84); Orinoco Basin…..Leptodoras
sp. 2 (Orinoco)
21A. Postorbital length 1.22–1.81 times
distance from snout tip to anterior nares; snout
length 41.6–46.5% of predorsal distance;
anterior scutes deep, covering >= half of
corresponding body depth; sum of midlateral
scutes 74–86; Orinoco and Amazon basins…..22
22A. Thin low middorsal ridge of adipose
tissue extending from adipose fin to point midway
between anterior base of adipose fin and posterior
base of dorsal fin; Upper Amazon Basin…..Leptodoras
acipenserinus
22B. Preadipose ridge absent or only
weakly developed, falling well short of point
midway between anterior base of adipose fin
and posterior base of dorsal fin; Orinoco Basin…..Leptodoras
sp. 1
