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KEY TO LEPTODORAS AND SELECT RELATED TAXA

(from unpublished doctoral thesis, Mark H. Sabaj, 2002)

* postorbital = distance from posterior orbit to dorsal-spine origin.

1A. Series of small plates along dorsal midline between dorsal fin and adipose fin.....2 (Hemidoras) 1B. No middorsal plates.....3
2A. Series of small plates along ventral midline between vent and anal fin; distal tip of dorsal fin dusky or black.....Hemidoras stenopeltis	Hemidoras stenopeltis
2B. No midventral plates; distal tip of dorsal fin hyaline.....Hemidoras morrisi	*Hemidoras morrisi*
3A. Maxillary barbels long, each with usually more than 14 secondary barbels; upper and lower lips not greatly extended beyond corners of mouth (if present, labial extensions usually much shorter than jaw barbels).....4 3B. Maxillary barbels rather short, each with usually less than 14 secondary barbels; upper and lower lips greatly extended beyond corners of mouth forming long and fleshy or membranous flaps (labial extensions occur in a variety of shapes, may be papillate or fimbriate, and are cojoined by an thinner, intervening membrane).....10 (Leptodoras)
4A. Sum of left and right midlateral plates less than 74; adipose eye absent or weakly developed.....5 4B. Sum of left and right midlateral plates usually greater than 74; adipose eye well developed.....Anduzedoras oxyrhynchus	Anduzedoras oxyrhynchus
5A. Nuchal foramina absent; anterior nuchal plate wide, laterally expanded and sutured to epioccipital (no suture between supraoccipital and middle nuchal plate).....6 (Doras) 5B. Nuchal foramina present; anterior nuchal plate variable.....7
6A. Midlateral plates becoming smaller anteriorly.....Doras micropoeus	Doras micropoeus
6B. Midlateral plates more or less uniform in size....Doras *carinatus*	Doras *carinatus*
7A. Distal tip of upper lobe of caudal fin dusky or black.....8 7B. Distal tip of upper lobe of caudal fin hyaline (not pigmented).....9
8A. Distal half of dorsal fin with conspicuous black spot or blotch; snout relatively pointed; primary and secondary maxillary barbels relatively smooth.....Hassar spp.	*Hassar orestis*
8B. Distal half of dorsal fin hyaline; snout rounded; primary and secondary maxillary barbels bearing small tertiary barbels.....Nemadoras leporhinus	Nemadoras leporhinus
9A. Snout constricted, narrowly compressed (gape very small); dorsal profile concave between tip of snout and posterior nares.....Nemadoras trimaculatus	*Nemadoras trimaculatus*
9B. Snout not constricted (gape normal); dorsal profile nearly straight between tip of snout and posterior nares.....Opsodoras ternetzi	Opsodoras ternetzi
10A. 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	Leptodoras sp. *4 (aff. myersi)*
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	Leptodoras hasemani
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	Leptodoras juruensis
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	Leptodoras myersi
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	*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	*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	Leptodoras sp. 3 (Negro form)
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)	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)	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*	Leptodoras *linnelli*
20B. Postorbital length 42.9–44.6% of predorsal distance…..Leptodoras sp. 2 (Orinoco)	Leptodoras sp. 2 (Orinoco)
21A. 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) 21B. 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	Leptodoras sp. 2 (Orinoco)
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*	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 (Apure/Meta)	Leptodoras sp. 1 (Apure/Meta)