Leptodoras Boulenger, 1898

Sabaj, Mark Henry, 2005, Taxonomic assessment of Leptodoras (Siluriformes: Doradidae) with descriptions of three new species, Neotropical Ichthyology 3 (4), pp. 637-678 : 642-646

Leptodoras Boulenger, 1898

Leptodoras Boulenger 1898:478 . Type species: Oxydoras acipenserinus Günther 1868 a , by subsequent designation of Eigenmann, 1910:395.

Diagnosis. Leptodoras is diagnosed from other genera of the Doradidae by unique modifications of the oral hood (upper labial extensions distinct, elongate and comparatively smooth with entire, scalloped or fimbriate lateral margins and interlabial membranes narrow or of moderate width), first gill arch (enlarged accessory lamellae on medial face of arch extend well onto medial face of gill filaments), and gas bladder (reduced size, modified cordiform shape, two distinct horn-like diverticula project from posterior walls of posterior chambers and pair of bulbous diverticula project from lateral walls of anterior chamber).

In Leptodoras the labial skin covering the jaws at the corners of the mouth continues posteriorly as a pair of long flap-like extensions ( Figs. 4 b-i, 5). These extensions are variously united by a thin and weakly papillate interlabial membrane.A thin membrane also joins the medial margin of lower labial extension to the outer jaw barbel. The lateral margin of upper labial extension is free from maxillary barbel and its origin roughly coincides with that of anteriormost 2° maxillary barbel. In all Leptodoras except L. praelongus and L. copei , the dorsalmedial surface of the lower labial extension is joined to a membranous fold (dorsolabial membrane, Fig. 1b ) that originates on ventrolateral corner of snout posterior to base of maxillary barbel. Higuchi (1992:220) also considered the oral hood to be uniquely derived among Leptodoras .

In Leptodoras enlarged accessory lamellae (each appearing as a column of soft lappets) occur along the medial face of the first gill arch and extend well onto the medial face of the gill filaments ( Fig. 6 ). In some Leptodoras ( cataniai , juruensis , myersi ), smaller accessory lamellae extend well onto the lateral face of the gill filaments and the gill rakers are absent or inconspicuous ( Fig. 6b ). Higuchi (1992:221) previously noted the morphology of the first gill arch as diagnostic of Leptodoras .

In Leptodoras the gas bladder has a modified cordiform shape and is reduced in overall size (i.e., shortened in particular; width greater than or equal to length) ( Fig. 7). Furthermore, in all Leptodoras there are: two distinct and relatively large horn-like diverticula that project from the posterior wall of the gas bladder, and discrete pairs of bulbous diverticula that project from the anterolateral walls on either side. The uniqueness of gas-bladder morphology in Leptodoras was first suggested by Eigenmann (1925).

brane is relatively thick with numerous papillae (vs. thin and few papillae in Leptodoras ). Some authors have suggested that the labial extensions (the upper in particular) are derived from the barbels (e.g., Günther 1868b:230; Boulenger 1898:478, Eigenmann 1925:357; Böhlke 1970:57). Based on their formation in Leptodoras and related taxa these structures appear to be modifications of the labial skin as indicated by Higuchi (1992:220).

The accessory lamellae on the gill arches in Leptodoras resemble to those of certain other doradids (e.g., Doras , Anduzedoras , Hassar , Hemidoras ). However, in these taxa the accessory lamellae are restricted to the medial face of the gill arch itself and do not extend onto the gill filaments.

In most other doradids the gas bladder is relatively large and often has an elongate cordiform shape. Other fimbriate- Comparisons. The oral hood in Leptodoras is most closely approximated among other doradids by Anduzedoras oxyrhynchus (Valenciennes) ( Fig. 4a ). In this monotypic genus the labial skin extends posteriorly beyond the corners of the mouth as flap-like structures united by an interlabial membrane. However, the labial extensions are relatively short and thickened, their ventral surfaces are rugose and papillate (vs. relatively smooth in Leptodoras ), and the interlabial mem- barbel doradids have a single medial posterior diverticula that may be simple (e.g., Doras carinatus ), split into two fingerlike projections joined at the base (e.g., Trachydoras ), or ornamented with small bulbous swellings or thin finger-like projections (e.g., Anduzedoras , Hassar ). Also unlike Leptodoras , the anterolateral walls of the gas bladder in other fimbriatebarbel doradids are smooth (e.g., Doras ) or variously ornamented with many bulbous (e.g., Anduzedoras ) or finger-like (e.g., Hassar , Hemidoras ) diverticula. Rhynchodoras (genus with simple barbels) also has a reduced gas bladder and one species ( R. woodsi ) has two posterior horn-like diverticula. However, in R. woodsi the lateral walls of the anterior chambers are smooth (vs. with a pair of bulbous diverticula in Leptodoras ).

Key to the species of Leptodoras .

1. Distal half of dorsal fin with distinct black spot or blotch ................................................... Leptodoras hasemani [p.653]

1’. Distal half of dorsal fin without black spot or blotch ........ 2

2. Dorsal spine thin and greatly extended as long flexible filament; predorsal distance relatively short, 26-28% of SL; bases of dorsal and paired fins with intense black pigment .......................................... Leptodoras juruensis [p.671]

2’. Dorsal spine rarely extended as a long flexible filament; predorsal distance longer,>30% of SL; pigmentation on bases of dorsal and paired fins variable ............................ 3

3. Broad dusky nuchal saddle extending ventrally across tympanum and humeral process, finishing on the lower side level withinsertionsofpairedfins .......... Leptodoras myersi [p.675]

3’. No dark nuchal saddle and bar on side of body ................ 4

4. Flap-like posterior extensions at corners of lower lip narrow and long, finishing beyond tips of similar extensions at corners of upper lip ( Figs. 4b,c ); black melanophores concentrated on basal portions of dorsal spine and, sometimes, fin; sum of midlateral plates usually <75 (range 70-76) ....... 5

4’. Flap-like posterior extensions at corners of lower lip relatively short, finishing even with or before tips of similar extensions of upper lip ( Figs. 4 e-g); base of dorsal fin without intense black pigmentation (may appear dusky, but never black); sum of midlateral plates usually>75 (range 74-92) ........................................................................ 6

5. 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 [p.647]

5’. 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 [p.649]

6. Upper labial extension relatively long with narrow base and expanded distal portion that curves medially and has a distinctly pointed or triangular-shaped tip ( Fig. 4g ); dorsolabial membrane well-developed, widely rounded posteriorly; postcleithral (humeral) process relatively short, usually 19.3-28.5 times into SL, and dorsal margin often obscured by overlying skin ...................................... 7

6’. Upper labial extension (excluding small fimbriae) with rounded or truncate distal tip ( Figs. 4e,f ); dorsolabial membrane weakly to moderately developed, evenly attenuate posteriorly; postcleithral (humeral) process longer, 13.9- 19.2 times into SL, and usually with well-defined margins .................................................................................................. 9

7. Adipose eye relatively large, horizontal length 1.5-1.8 times into postorbital distance and 23.1-27.8% of predorsal distance; blackwaters of Negro and Casiquiare ........................... ................................................ Leptodoras cataniai [p.667]

7’. Adipose eye smaller, horizontal length 1.8-2.3 times into postorbital distance and 18-23.2% of predorsal distance; white to moderately blackwaters of Amazon basin .......... 8

8. Snout relatively long, length 1-1.2 times postorbital distance, 42.4-46.6% of predorsal distance; sum of midlateral plates 79-86 (modally 82) ........................................................... ........................ Leptodoras cf. cataniai (Nanay form) [p.670]

8’. Snout shorter, length 0.8-1 times postorbital distance, 37.6- 41.3% of predorsal distance; sum of midlateral plates 83- 92 (modally 88) ............................................................................ ..................... Leptodoras cf. cataniai (Amazon form) [p.669]

9. Adipose eye relatively large, horizontal length 20.3-24.8% of predorsal distance and 11.2-13.9 times into SL; predorsal distance relatively long, 35.5-38.7% of SL; thin low preadipose ridge always present ........................................... 10

9’. Adipose eye smaller, horizontal length 15.4-19.1% of predorsal distance and 14.5-20.6 times into SL; predorsal distance somewhat shorter, 31.6-35.6% of SL; preadipose ridge absent or only weakly developed ........................... 11

10. Postorbital length 37.6-41.8% of predorsal distance ............ ....................................................... Leptodoras linnelli [p.654]

10’. Postorbital length 42.9-44.6% of predorsal distance ........... ................................................ Leptodoras rogersae [p.665]

11. Postorbital distance 1.8-2 times distance from snout tip to anterior nares; snout length 37.8-41.8% of predorsal distance; anterior midlateral plates comparatively shallow, covering between 1/4 and 1/2 of corresponding body depth; sum of midlateral plates 82-86 (modally 84); Orinoco basin ..................................... Leptodoras rogersae [p.665]

11’. Postorbital distance 1.2-1.8 times distance from snout tip to anterior nares; snout length 41.6-46.5% of predorsal distance; anterior midlateral plates deep, covering half or more of corresponding body depth; sum of midlateral plates 74-86; Orinoco and Amazon basins ..................... 12

12. 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 [p.658]

12’. 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 nelsoni [p.663]

Figures

Fig. 4. Variation in oral-hood morphology in Anduzedoras and Leptodoras. a. A. oxyrhynchus,ANSP 160628 (SL 124.6 mm). b. L.praelongus,ANSP162464 (SL 124.9 mm).c.L.copei,ANSP 162461 (SL95.9 mm).d. L.hasemani,ANSP 175889(SL86.7 mm). e. L. linnelli,ANSP 175883 (SL 94 mm). f. L. nelsoni, MCNG 13167 (SL 93 mm). g. L. cataniai,ANSP 161533 (SL 162.5 mm).h. L. juruensis, INHS 39465 (SL 117.4 mm). i. L. myersi,ANSP 112319 (SL 72.6 mm).

Fig. 1. Standard terminology for features of barbels and labial structures in Leptodoras. a. Ventral view of head in L. linnelli, ANSP 175883 (SL 94 mm).b.Lateral view of headin L. nelsoni, MCNG13167(SL93mm).

Fig. 6. Lateral (left) and medial (right) views of 1st gill arch.a. Leptodoras copei,ANSP162466 (SL 141.5 mm).b.Leptodoras cataniai,ANSP 161532 (SL 148 mm).