Leptodoras nelsoni, Sabaj, 2005

Sabaj, Mark Henry, 2005, Taxonomic assessment of Leptodoras (Siluriformes: Doradidae) with descriptions of three new species, Neotropical Ichthyology 3 (4), pp. 637-678 : 663-665

Leptodoras nelsoni , new species

Figs. 4f , 5b , 15d and 20

Holotype. ANSP 180917 (1*, 117 mm), Colombia, Meta, río Metica (Meta-Orinoco dr.), ca. 1.5 km east of Rajote, Plancha 267 (3°56’N, 73°3’W), 19 Mar 1973, W.G. Saul and W.F. Smith- Vaniz, BSS-14.

Paratypes (35). Colombia: Meta: AMNH 236112 [ex. ANSP 134667 ] (1, 103.7 mm), río Metica (Meta-Orinoco dr.), ca. 3 km southeast of Hacienda Mozambique (3°57’N, 73°2’W), 30 Mar 1975, BSF-26; ANSP 131336 (2, 99.2-111 mm), same data as holotype ; ANSP 134665 (2 + 1*, 113.8 mm), Río Metica (Meta- Orinoco dr.), ca. 3 km southeast of Hacienda Mozambique (3°57’N, 73°2’W), 24 Mar 1975, BSF-9; ANSP 134666 (1, 86.9 mm), río Metica (Meta-Orinoco dr.), ca. 3 km southeast of Hacienda Mozambique (3°57’N, 73°2’W), 20 Mar 1975, BSF- 1; ANSP 134667 (1 + 1*, 92.3 mm), same data asAMNH 236112; AUM 28764 (1, 75.5 mm), río Manacacías (Meta-Orinoco dr.), 7 km south-southeast of Puerto Gaitán at sandbar on left (west) bank , 9 Oct 1978, JSR 78-35; CAS 222740 [ex. ANSP 134665 ] (1*, 97.9 mm), same data as ANSP 134665; FMNH 117083 [ex. ANSP 134665 ] (1, 104.7 mm), same data as ANSP 134665; ICNMHN 13571 [ex. ANSP 134667 ] (1, 95 mm), same data as AMNH 236112; MNHN 2003-0355 [ex. ANSP 134665 ] (1), UMMZ 245737 [ex. ANSP 134665 ] (1 + 1*, 105.5 mm), USNM 384342 [ex. ANSP 134665 ] (1*, 116.7 mm), same data as ANSP 134665. Venezuela: Apure: ANSP 179101 (1, 100 mm), río Apure (Orinoco dr.), upriver of San Fernando and downriver of mouth of río Portuguesa, JNB-84- V4 ; ANSP 182200 [ex. MBUCV-V 14769 ] (1*, 162 mm), ríoApure (Orinoco dr.), isla del medio (extremo oeste) , 7 Aug 1984; MBUCV-V 10941 (1, 104 mm), río Apure ( Orinoco dr.), frente a isla Apurito , 5 Apr 1978; MBUCV-V 14769 (1 + 3*, 93.3-135.8 mm), same dataasANSP 182200; MBUCV-V 15215 (1, 101.9 mm), ríoApure (Orinoco dr.), in front of Jarina lagoon , 25 Jan 1984; MBUCV- V 23693 (4, 105- 131 mm), caño Bucaral ( Orinoco dr.), hacia la boca con elArauca , 9 Aug 1984; MBUCV-V 24649 (2, 124, 151 mm), río Apure ( Orinoco dr.), in front of Jarina lagoon, near San Fernando de Apure , 21 May 1983; MBUCV-V 24659 (3, 105- 128 mm), río Apure (Orinoco dr.), frente al Aeuropuerto , 18 Feb 1982; MCNG 13167 (1, 93.0 mm), río Apure ( Orinoco dr.), 12 km rio abajo de San Fernando de Apure , 16 May 1985, DCT85-13.

Non-type material (7). Colombia: ANSP 149924 (1, 69.6 mm), río Meta (Orinoco dr.), Llanos District near Bogota, pre-1973 ; FMNH 73408 (1, 75.0 mm), río Guaviare (Orinoco dr.), near Mapiripana (2°45’N, 71°W), Dec 1957, SW 57-1 . Venezuela: Apure: MBUCV- V 10856 (2), río Apure (Orinoco dr.), Aeropuerto de San Fernando de Apure, 21 Jan ? 1958 ; MBUCV-V 10879 (1, 58.2 mm), río Apure (Orinoco dr.), Jan? 1951 ; MCNG 13887 (1 + 1*, 123.5 mm), río Apure (Orinoco Dr.), 10 km rio abajo de San Fernando de Apure, 15 May 1985, DCT85-11 .

Diagnosis. Distinguished among Leptodoras by the following combination: upper labial extension L-shaped, distal half moderately to strongly curved and distinctly expanded with wide lateral flap bearing small fimbriae, sum of midlateral plates modally 78, plates deep, covering more than 1/2 of body depth, adipose eye weakly developed, preadipose ridge lacking.

Description. Morphometrics summarized in Table 1. Overall shape nearly identical to that of L. acipenserinus ; body very elongate and dorsoventrally depressed, ventrally flattened from snout to vent; head depressed, short relative to body with long acute snout; dorsal profile of snout shallowly convex from tip to midway between nares; caudal peduncle long, shallow, depressed. Eye moderately sized, more or less centered between snout tip and origin of dorsal-spine, adipose eyelid weakly developed.

Mouth subterminal, jaws edentulous in adults and juveniles as small as 70 mm SL; smaller specimens not examined, but expected to have few thin acicular teeth near medial symphysis of dentaries. Maxillary barbel long, usually reaching ventromedial extent of gill opening. Secondary maxillary barbels 8-11 (modally 10), flattened, overlapping proximally, separated distally; proximal secondary maxillary barbels with fimbriate anterior margin and smooth posterior margin; distal ones smooth. Oral hood comparatively short overall, not greatly expanded posteriorly, morphology similar to that of L. acipenserinus . Upper labial extension elongate, somewhat Lshaped, proximal half straight and narrow, distal half moderately to strongly curved medially and distinctly expanded with wide lateral flap bearing small fimbriae, surface smooth. Lower labial extension narrow, attenuate, finishing before upper labial extension. Interlabial membrane narrow (labial extensions convergent), comparatively thin with few small papillae. Dorsolabial membrane weakly developed, evenly attenuate posteriorly. Two pairs of jaw barbels with scattered elongate papillae; cojoined by basal membrane; outer pair slightly longer than inner pair and shorter than maxillary barbel, cojoined with lower labial extension via narrow membrane. Branchiostegal membrane with narrow fleshy margin weakly overlapping ventral gill opening; fleshy inner flap along cleithrum nearly complete. Morphology of first gill arch similar to L. linnelli .

Sum of midlateral plates 74-80 (modally 78, Table 3). Anterior midlateral plates moderately deep, covering about half of corresponding body depth; posterior margins of dorsal and ventral wings rounded with many small serrae. Tympanum usually with 3 distinct ossifications (simple or dual spines) along postotic laterosensory canal; small fixed spine usually conspicuous along posterior margin of neurocranium where postotic laterosensory canal exits supracleithrum. Postcleithral process short and deep, distal portion dome shaped with straight ventral margin. Subrectangular nuchal foramina present, replacing suture between epioccipital and anterior nuchal plate. Middorsal groove on nuchal shield usually well defined. Skin with many small fleshy papillae on dorsal surface and sides of snout, papillae somewhat enlarged on medial portion.

Dorsal-fin rays I,6; pectoral-fin rays I,9-11 (modally 10); pelvic-fin rays i,6; total anal-fin rays 14-17 (first 4 to 6 unbranched); caudal-fin rays i,8/9,i; dorsal procurrent caudalfin rays 14-18, ventral procurrent caudal-fin rays 12-16. Dorsal-fin spine of moderate length and width, nearly straight, evenly attenuate with sharp tip; anterior denticulations antrorse, moderately sized and crowded basally, absent from distal tip; posterior denticulations weakly retrorse to straight, weak, rather inconspicuous. Pelvic fins of moderate length with rounded to weakly pointed distal margin. Pectoral-fin spine, anal fin and caudal fin as described for L. acipenserinus .

Coloration in alcohol. Coloration of L. nelsoni is largely as described for L. acipenserinus with two exceptions: divergent pair of dusky stripes on caudal fin very distinct and nuchal foramina often dark gray with dense concentration of melanophores in overlying skin.

Distribution and habitat. Leptodoras nelsoni is presently known from a few east-flowing tributaries of the middle Orinoco: río Guaviare and upper Meta in Colombia and río Apure in Venezuela ( Fig. 16 ). Its distribution likely encompasses other large left-bank tributaries of the Orinoco throughout the cis-Andean piedmont and llanos. Leptodoras nelsoni presumably occupies large river habitats similar to those noted for L. acipenserinus (e.g., whitewaters, swift currents near sandy beaches).

Etymology. Named in honor of Douglas Nelson, for his dedicated service to the ichthyological community since 1983 as Collection Manager of Fishes, University of Michigan Museum of Zoology.

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. 5. Ventral views of heads in Leptodoras. a. L. linnelli, MBUCV-V 16602 (SL 157 mm). b. L. nelsoni, MBUCV-V 14769 (SL 135.8 mm). c. L. rogersae, USNM 226307 (SL 180 mm). d. L. acipenserinus, FMNH 92385 (SL 155 mm). e. L. acipenserinus, FMNH97140 (SL 113.3 mm).f.L.acipenserinus,ANSP 178467 (SL 107.9 mm). g. L.cataniai,ANSP 161532 (SL 142.6 mm).h. L. cf. cataniaiAmazon form,ANSP 180925 (SL 194 mm). i. L. cf.cataniai Nanay form,ANSP 178438 (SL 164.2 mm).

Fig. 15. Juvenile and subadult Leptodoras (Orinoco and Essequibo basins). a. L. linnelli, ANSP 175881 (SL 100.1 mm), Essequibo river, Guyana. b. L. linnelli, MBUCV-V 19689 (SL 100.5 mm), río Mavaca (Orinoco dr.), Amazonas, Venezuela.c. L. rogersae, paratype, MBUCV-V 13372 (SL 128.8 mm), río Orinoco, DeltaAmacuro, Venezuela. d. L. nelsoni, paratype, MBUCV- V 14769 (SL 104.5 mm), ríoApure,Apure, Venezuela.

Fig. 20. Leptodoras nelsoni, paratypeANSP 182200 (SL 162 mm), ríoApure (Orinoco dr.),Apure, Venezuela.

Fig. 16. Distributions of Leptodoras acipenserinus (solid red circles), L. linnelli (solid green circles), L. nelsoni (open red circles) and L. rogersae (open blue circles) (stars denote type localities).