Leptodoras praelongus ( Myers & Weitzman, 1956 )

Sabaj, Mark Henry, 2005, Taxonomic assessment of Leptodoras (Siluriformes: Doradidae) with descriptions of three new species, Neotropical Ichthyology 3 (4), pp. 637-678 : 647-649

Leptodoras praelongus ( Myers & Weitzman, 1956)

Figs. 4b , 7a and 8

Hassar praelongus Myers & Weitzman 1956: 2 , fig. 1

(type locality: São Gabriel Rapids of the rio Negro (Amazonas dr.), Amazonas, Brazil).

Diagnosis. Uniquely distinguished among Leptodoras by shallow midlateral plates covering <1/4 body depth (vs.>1/ 4 in all other species), and anterior nuchal plate usually of moderate width (longer than wide) permitting weak to firm suture between supraoccipital and middle nuchal plate (vs. anterior nuchal plate laterally expanded, sharing broad suture with epioccipital or forming dorsal border of nuchal foramina).Also distinguished from all Leptodoras except L. copei by having distal tip of lower labial extension extending beyond that of upper labial extension.

Description. Overall shape (excluding caudal fin) lenticular, weakly compressed, ventrally flattened from snout to vent; head deep with prominent conical snout; body elongate, caudal peduncle short, depressed. Eye large with well-developed adipose eyelid.

Mouth subterminal, jaws edentulous in adults, juveniles <55 mm SL often with one or two small acicular teeth on distal-medial surface of each dentary (aside symphysis). Maxillary barbel of moderate length, usually finishing short of ventromedial extent of gill opening. Secondary maxillary barbels 7-10 (modally 9), flattened, largely overlapping; proximal secondary maxillary barbels with fimbriate anterior and posterior margins; distal ones smooth. Upper labial extension lanceolate (tapered distally), moderately elongate, comparatively thick, straight to weakly curved medially, ventral surface smooth or weakly rugose (sometimes with small papillae medially), lateral margin scalloped or with triangular fimbriae distally. Lower labial extension long (extends beyond upper labial extension), narrow, attenuate and straight; medial margin and tip with small papillae or fimbriae. Interlabial membrane of moderate width, slightly expanded distally (labial extensions divergent), comparatively thin with small papillae and free distal margin. Dorsolabial membrane absent. Two pairs of jaw barbels well-ornamented with elongate papillae and cojoined by basal membrane; outer pair only slightly longer than inner pair, shorter than maxillary barbel, and cojoined with lower labial extension via narrow membrane. Branchiostegal membrane with thin fleshy margin moderately overlapping ventral gill opening; fleshy inner flap along anteroventral face of cleithrum incomplete, not reaching cleithral notch for pectoral spine insertion. First gill arch with 15-20 moderately developed gill rakers (length about 4 times width); accessory lamellae on medial face of arch continuing well onto medial face of gill filaments (present on every third or fourth filament); each accessory lamella appears as a column of lappets with first one (opposite rakers) enlarged and deflected medially; accessory lamellae absent on lateral faces of gill arch and filaments.

Sum of midlateral plates 70-76 (modally 72 or 74, Table 3 ). Anterior midlateral plates shallow, covering less than 1/4 of corresponding body depth; posterior margins of dorsal and ventral wings rounded with small serrae. Tympanum without superficial ossifications or occasionally with 1 to 3 very small, weak spines along postotic laterosensory canal. Postcleithral process of moderate length and nearly uniform width, somewhat trapezoidal in shape. Middorsal groove on nuchal shield weakly defined. Nuchal foramina absent. Skin relatively smooth.

Dorsal-fin rays I,6; pectoral-fin rays I,8-10 (modally 9); pelvic-fin rays i,6; total anal-fin rays 14-15 (first 4 or 5 unbranched); caudal-fin rays i,8/9,i; dorsal procurrent caudalfin rays 14-17, ventral procurrent caudal-fin rays 13-16. Dorsal-fin spine long, moderate width, weakly curved and evenly attenuate with slender distal tip; anterior denticulations antrorse, small and crowded basally, absent from distal quarter; posterior denticulations retrorse, separated and well formed nearly to tip. Pectoral-fin spine sturdy, of moderate length, gently bowed with sharp tip; anterior denticulations antrorse, small and absent from distal quarter; posterior denticulations retrorse, decreasing in size from midlength to tip; last posterior denticulation subterminal. Pelvic fin short with straight distal margin. Anal fin triangular, tip of longest branched ray more or less even with vertical through base of last ray, distal margin shallowly concave. Caudal fin forked with rounded to weakly pointed lobes.

Coloration in alcohol. Head and body weakly countershaded, upper sides relatively uniform tan or gray-brown, lower sides (below midlateral plates) occasionally dusky with scattered melanophores (particularly in juveniles wherein the depigmented midlateral plates form white midlateral stripe), undersurfaces white to cream. Melanophores sometimes weakly concentrated in skin between and above dorsal wings of midlateral plates, effecting appearance of faint dusky stripe. Dorsal fin with large sub-basal black blotch on dorsal spine, first fin ray and intervening membrane; blotch often expanded posteriorly as dark wedge-shaped band across entire base of fin. Pectoral fin with melanophores concentrated along base and forming radiate streaks on distal membranes (fin rays relatively depigmented). Pelvic fin occasionally with similar but lighter pattern (fewer melanophores).Anal fin cream, hyaline, occasionally with few scattered melanophores. Caudal fin with melanophores forming black streaks on lower membranes of upper lobe and upper membranes of lower lobe, remaining portion cream, hyaline.

Distribution and habitat. Leptodoras praelongus is known from Brazil and Venezuela in the upper río Orinoco (upstream of Puerto Ayacucho), rio Negro, rio Tocantins, several localities along the rio Amazonas (between the rios Jutaí and Madeira), and one site in the Madeira basin ( Fig. 9 ). Many collecting sites are associated with large river cataracts. Most records are from blackwaters. However, a few are from whitewater rivers (e.g., rios Branco and Madeira), and one is from a clearwater river (rio Tocantins).

Type-material examined. Leptodoras praelongus : holotype (unique), CAS 148679 [ex. SU 48679] (1, 112.25 mm), rio Negro , Amazonas dr. , São Gabriel rapids, Amazonas, Brazil, 1 Feb 1925, C. Ternetz.

Non-type material. Brazil: Amazonas: ANSP 178538 (1), rio Madeira ( Amazonas dr. ), 9 km upstream from Vila Urucarituba (3°35’28"S, 58°56’53"W), 6 Aug 1996, CCF-96-78; ANSP 180908 (3), rio Jutaí ( Solimões dr. ), between Pto. Antunes and Foz do Jutaí (2°50’6"S, 66°55’39"W), 13 Nov 1993, JPS-93-049; ANSP 180909 (1), rio Jutaí ( Solimões dr. ), between Pto. Antunes and Foz do Jutaí (2°49’39"S, 66°54’55"W), 13 Nov 1993, OTO-93-033; ANSP 180910 (3), rio Negro ( Amazonas dr. ), 37.8 km upstream from Carvoeiro (1°12’27"S, 62°15’3"W), 10 Dec 1993, MG-93-037; ANSP 180911 (2), rio Negro ( Amazonas dr. ), 10 km downstream from Carvoeiro (1°22’8"S, 61°54’22"W), 9 Dec 1993, JGL-93- 190; ANSP 180912 (3), rio Negro ( Amazonas dr. ), 3.8 km downstream from S. Francisco (1°41’10"S, 61°27’3"W), 6 Dec 1993, JPF-93-158; ANSP 180913 (1, 40.2 mm), rio Negro ( Amazonas dr. ), 5 miles downstream from Santa Maria (3°0’49"S, 60°24’31"W), 18 Jul 1996, MTP-96-007; ANSP 180916 (1), rio Jutaí ( Solimões dr. ), downstream of Pto. Antunes and upstream of Copatana (2°56’52"S, 67°00’32"W), 16 Nov 1993, OTO-93-057; INPA ex. 17709 (4), rio Demini ( Negro dr. ), near mouth of rio Aracá , 22 Jun 1993; INPA 17727 (15), rio Negro ( Amazonas dr. ), near mouth of rio Branco , 13 Nov 1996; INPA 17761 (1, 112.1 mm), INPA 17764 (3, 65.6-158 mm), rio Negro ( Amazonas dr. ), igarapé Zamula , near Barcelos, 19 Nov 1996; INPA 17907 (1, 111.1 mm), rio Negro ( Amazonas dr. ), at mouth of rio Branco , 4 Feb 1998. Para: ANSP 180914 (2), rio Amazonas ( Atlantic dr. ), 24 km upstream from Gurupa, 6 km downstream of mouth of rio Xingu (1°28’12"S, 51°49’43"W), 14 Nov 1994, AMZ-94-100. Rondônia: INPA uncataloged (3, 156- 185 mm), rio Jamari ( Madeira dr. ), at and a little upstream of Ariquemes, downstream of mouth of rio Camaã , 15 Nov 1983. Roraima: ANSP 178534 (1), rio Branco ( Negro dr. ), between Atauba and Caruna, 9.3 km above confluence with rio Negro (1°19’34"S, 61°52’13"W), 8 Dec 1993, JGL-93-171; ANSP 180915 (3), rio Branco ( Negro dr. ), downstream of Atauba and upstream of Caruna (1°17’55"S, 61°51’21"W), 8 Dec 1993, JGL-93-174; INPA 2004 (1, 147.3 mm), rio Tacutu ( Branco dr .), 17 Mar 1988; USNM 332438 (2), rio Branco ( Negro dr. ), 25 Sep 1992. Tocantins: UNT 153 [ex. 3080] (1), rio Tocantins ( Atlantic dr.), fazenda Traçadal , near Paranã City (12°29’S, 48°12’W), 3 Oct 2000. Venezuela: Amazonas: ANSP 162463 (3, 141.4- 173 mm), río Pamoni ( Casiquiare dr.) , ca. 0.5 km from confluence with Casiquiare (2°49’N, 65°55’W), 18-19 Mar 1987, V87-34; ANSP 162464 (4, 120.24- 127.9 mm), río Casiquiare , main channel, ca. 1.5 hrs from its confluence with Orinoco (3°5’N, 65°55’W), 16 Mar 1987, V87-24; ANSP 162465 (3, 118- 166.8 mm), río Casiquiare , from mouth of río Pamoni to 4 km below (2°48’N, 65°57’W), 17 Mar 1987, V87- 27; ANSP 165791 (1, 31.25 mm), río Sipapo ( Orinoco dr. ), along playas of sand and rock ca. 1-4 km above Pendare (4°51’N, 67°44’W), 12 Nov 1985, V85-8; ANSP 165793 (6, 34.76-49.2 mm), río Sipapo ( Orinoco dr. ), ca. 3-4 km upstream from Pendare (4°52’N, 67°43’W), 12 Nov 1985, V85-5; MBUCV-V 25602 (1, 151.0 mm), río Canucunuma ( Orinoco Dr. ), desde campamento 2 km rio abajo, 40 km sobre boca en río Orinoco , 23 Mar 1987; MBUCV-V 25603 (2), río Casiquiare , canal principal ca. 1.5 hrs des de boca en río Orinoco , ca. 1 hr rio abajo, 23 Mar 1987; MBUCV-V 25664 (1, 134.7 mm), same data as ANSP 162465 .

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. 7. Ventral views of gas bladders in situ (arrows denote bony capsules of enlarged first vertebra). a. Leptodoras praelongus, ANSP 162463 (SL 142 mm). b. Leptodoras cf. cataniai, Nanay form, INHS 39814 (SL 111.1 mm).

Fig. 8. Leptodoras praelongus, MBUCV-V 25602 (SL 151 mm), río Canucunuma (Orinoco dr.), 40 km upstream from the mouth, Amazonas, Venezuela.

Fig. 9. Distribution of Leptodoras praelongus (star denotes type locality). Color overlays approximate water conditions as moderate to extreme blackwaters (gray), sediment-rich whitewaters (brown), mixed black/whitewaters (tan) and predominantly clearwaters (blue). Drainage base map by M. Weitzman.

Tables

Table 3. Frequency distribution of sum of midlateral plates in Leptodoras (modal numbers in squares; count begins with infranuchal plate).

	70	71	72	73	74	75	76	77	78	79	80	81	82	83	84	85	86	87	88	89	90	91	92	Mean	n
Leptodoras praelongus	2	2	5	3	5	3	1																	73	21
Leptodoras copei	1	5	7	1	1																			71.7	15
Leptodoras hasemani						1	3	4	11	4	2													77.8	25
Leptodoras linnelli					2	3	29	12	18	13	6	4												77.4	87
Guianas, NE Brazil					2	3	27	12	10	2	3													76.7	59
Upper Orinoco							2		8	11	3	4												78.9	28
Leptodoras nelsoni					1	5	4	8	9	7	1													77.3	35
Leptodoras rogersae													6	8	8	6	2							83.7	30
Leptodoras acipenserinus								1	4	8	3	1	13	5	3		1							81.1	39
Madeira, Itaya, Nanay								1	4	8	2	1	1											79.1	17
Marañon, Ucayali, Napo											1		12	5	3		1							82.6	22
Leptodoras cataniai & cf. catania										2	3	3	13	14	16	6	7	3	5	3	4		2	84.4	81
cataniai													4	7	10	4	4	2						84.1	31
Amazon form														1		2	2	1	5	3	4		2	88.2	20
Nanay form										2	3	3	9	6	6		1							82.2	30
Leptodoras juruensis																				1	7	3		90.2	11
Leptodoras myersi					3	2	3	1	1	1														75.8	11