Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge Author Sullivan, John P. Author Zuanon, Jansen Author Cox Fernandes, Cristina text ZooKeys 2013 327 1 34 http://dx.doi.org/10.3897/zookeys.327.5427 journal article http://dx.doi.org/10.3897/zookeys.327.5427 1313-2970-327-1 Brachyhypopomus (Odontohypopomus) bennetti sp. n. Figs 6, 7, Appendix I; Tables 2, 3 Holotype. INPA 39560 (ex-8941), tag no. 93-220, 215 mm TL, 176 mm LEA, female, Amazonas, Brazil: floating meadow along side of lake in the Parana do Paracuuba , near mouth of Rio Negro and entrance to Lago Janauari, approx. 15 km due south of Manaus, 03°12.6'S , 059°59.40'W , J.P. Sullivan and J. Zuanon, 23 April 1993. Paratypes (18). Brazil: Amazonas: INPA 39561 (1 cs, tag no. 93-221, 95 mm LEA, damaged), same data as holotype; INPA 39579 (1 alc, tag no. 93-26, 152 mm LEA, damaged), Ilha da Marchantaria, approx. 03°14'S , 059°59'W , J.P. Sullivan & J. Zuanon, 5 March 1993; INPA 8862 (2 alc, tag nos. 93-139, 93-163, 152 mm & 162 mm LEA, respectively, damaged), Parana do Paracuuba near holotype locality, J.P. Sullivan & J. Zuanon, 14 April 1993; INPA 8863 (1 alc, tag no. 93-222, 145 mm LEA, damaged), Lago Janauari & Parana do Paracuuba near holotype locality, J.P. Sullivan & J. Zuanon, 24 April 1993; INPA 39578 (1 alc, tag no. 93-54, 153 mm LEA, damaged), Parana do Paracuuba near holotype locality, J.P. Sullivan & J. Zuanon, 24 March 1993; INPA 39580 (3 alc, 2 damaged: tag nos. 93-112, 93-113, 160 &170 mm LEA respectively , 1 intact: tag no. 93-116, 161 mm LEA), same data as for holotype; INPA 8940 (3 alc, all intact, tag nos. 93-137, 93-141, 93-165, 167-171 mm LEA), lake between Janauari and Solimoes , approx. 03°12.6'S , 060°01.9'W , J.P. Sullivan & J. Zuanon, 14 April 1993; INPA 39581 (1 alc, tag no. 93-214, 150 mm LEA, intact), same data as previous; ANSP 194034 (1 alc, tag no. JPS-93-44/1, 125 mm LEA, intact), floating grasses directly in front of town of Fonte Boa, 02°30.57'S , 066°05.72'W , J.P. Sullivan, 11 November 1993; ANSP 194035 (1 alc, tag no. JPS-93-57/1, 89 mm LEA, intact), Rio Jutai near mouth into Solimoes , floating grasses and water hyacinth, approx. 02°40'S , 066°40'W , J.P. Sullivan, 16 November 1993; CUMV 97640 (3 alc, 1 intact: tag no. JPS-93-37/1, 98 mm LEA, 2 damaged: tag nos. JPS-93-37/2, JPS-93-37/3, 118 & 75 mm LEA, respectively), Rio Jurua near mouth into Solimoes , approx. 02°40'S , 065°45'W , floating vegetation, J.P. Sullivan, 8 November 1993. Non-types. Bolivia: Beni: Rio Beni drainage: CAS 72216 (1 alc, 126 mm LEA), Reyes, 24 mi. NE of Rurrenabaque on the pampas, approx. 14°17'S , 067°20' W , N.E. Pearson, Mulford Expedition, 15 November 1921; CAS 81631 (1 alc, size n.a.), data same as for previous. Brazil: Amazonas: Rio Solimoes drainage: INHS 70542 (5 of 10, alc, 71-162 mm LEA), Ilha da Marchantaria south of Manaus, approx. 03°14'S , 059°58' W , P. Bayley, 14 March 1978; MCZ 78163 (1 of 8, alc, 98 mm LEA,) Lago Jacaretinga near Manaus, T.J. Zaret et al., 5 November 1979; USNM 306841 (1 alc, 147 mm LEA), Parana do Lago Januauaca , entrance to Lago do Castanho, 0-2.1 meters depth, P. Bayley, 30 March 1977; USNM 306859 (1 alc, 72 mm LEA), Lago Terra Preta, Janauari, depth 0-1 meter, P. Bayley, 3 August 1977; USNM 306875 (1 alc, 131 mm LEA), Lago Janauari, near its outflow, depth 0.6-1 meters; USNM 306929 (10 alc, 71-139 mm LEA), Lago Camaleao , near Manaus within Ilha da Marchantaria, P. Bayley, 28 March 1977; USNM 306947 (1 alc, 96 mm LEA), collection locality same as for previous, P. Bayley, 29 March 1977; INPA 13569 (2 alc), Iranduba, Ilha da Marchantaria, Lago Camaleao , P. Petry & R. Sotero, 3 April 1993; INPA 33255 (3 alc), Manaus, Ilha da Paciencia , 03°16.68'S , 060°16.58'W , L. Rapp Py-Daniel et al., 18 September 2003; INPA 32091 (3 alc), Manaus, Lago do Rei, J.I.S. Botero, 30 June 1998; INPA 6403 (5 alc), Iranduba, Lago Janauaca , INPA staff, 12 September 1979; INPA 39563 (4 alc), Coari, 03°51.17'S , 063°28.12'W , L. Rapp Py-Daniel et al., 13 September 2003; INPA 33270 (3 alc), Fonte Boa, Lago "Ressaca Grande", 02°28.43'S , 066°09.28'W , J. Zuanon et al., 8 September 2003; INPA 39562 (5 alc, 54.9-144.1 LEA), Sao Paulo de Olivenca , Rio Camatia , comunidade Monte Sinai, approx. 03°27.57'S , 068°56.00'W , L. Rapp Py-Daniel et al., 4 April 2008; ANSP 194026 (4 alc, 65.1-132.6 mm LEA), same data as previous; INPA 18244 (6 alc) Alvaraes , Lago Geraldo, Reserva Mamiraua , W.G.R. Crampton, 29 May 1998; INPA 18245 (4 alc), Alvaraes , Lago Curuca Aberto, Reserva Mamiraua , W.G.R. Crampton, 1 June 1998; INPA 18246 (3 alc), Alvaraes , Lago Curuca Comprido, Reserva Mamiraua , W.G.R. Crampton, 2 June 1998; INPA 15816 (34), INPA 18241 (1 alc), INPA 18242 (1 alc), INPA 18243 (1 alc), INPA 18348 (1 alc), INPA 18349 (1 alc), INPA 18350 (1 alc), 18351 (2 alc), INPA 18352 (1 alc), INPA 18354 (3 alc), Alvaraes , Lago Mamiraua system, W.G.R. Crampton, 1 April 1997-18 May 1998; INPA 18355 (3 alc), Alvaraes , Lago Mamiraua , Lago Promessa, W.G.R. Crampton, 19 May 1998; INPA 18357 (3 alc), Alvaraes , Lago Curuca , Lago Mamiraua system, W.G.R. Crampton, 30 May 1998; INPA 18358 (2 alc), Alvaraes , Lago Miratinin, Lago Mamiraua system, W.G.R. Crampton, 4 June 1998; INPA 18361 (2 alc), Lago Apolonio , Lago Mamiraua system, W.G.R. Crampton, 1 July 1999; INPA 18362 (1 alc), Lago Secretaria , Lago Mamiraua system, W.G.R. Crampton, 9 June 2000; INPA 33196 (1 alc), Tabatinga, Comunidade Palmares, 03°57.89'S , 069°20.19'W , J. Zuanon et al., 2 September 2003. Rio Jutai drainage: INPA 33187 (3 alc), Ressaca do Luizinho, 02°42.98'S , 066°48.22'W , J. Zuanon et al., 6 September 2003. Para : Rio Amazonas drainage: INPA 39564 (1 alc), Almeirim, Comunidade Paranaguara, 01°44.48'S , 053°10.25'W , J. Zuanon et al., 5 October 2003. Rio Tapajos drainage: INPA 39518 (1 alc), Belterra, Igarape do Indio near mouth to Rio Tapajos , 02°40'S , 054°58'W , F.R. Ribeiro, 26 December 2008. Colombia: Amazonas: Rio Amazonas drainage: FMNH 85363 (38 alc, 67-153 mm LEA), Rio Amazonas 2-3 miles upstream of Leticia, approx. 04°05'S , 070°03'W , Na varro , Thomerson et al., 13 November 1973; USNM 216870 (1 alc, 110 mm LEA), Leticia, D. Kramer, 4 December 1974. Ecuador: Napo: Rio Napo drainage: FMNH 102270 (2 alc, 56 & 110 mm LEA), Laguna de Limoncocha, D. Stewart et al., 4 Oc tober 1981. Peru: Loreto: Rio Ucayali drainage: AMNH 78060 (7 of 14, alc, 81-101 mm LEA), several sites along 10 km stretch, Ferraris, Montrevil et al., 7 July 1987. Diagnosis. Brachyhypopomus (Odontohypopomus) bennetti sp. n. is diagnosed by two character states in addition to those used to diagnose the subgenus Odontohypopomus above: (1) electric organ along caudal filament and along body above anal fin exceedingly deep and visible as large semi-translucent area, occupying approximately 14-17% body depth directly posterior to abdominal cavity; (2) monophasic, head-positive EOD, approximately 2.1 milliseconds in duration in both sexes at 25°C. The appearance of the electric organ in this species when backlit (Fig. 8) is significantly larger than in any other species of Brachyhypopomus . No other described Brachyhypopomus has a monophasic EOD waveform. This species can be distinguished from the similar Brachyhypopomus walteri sp. n. by a longer body (depth gradually tapers posteriorly: depth of body at 40th post-abdominal vertebra 46-57% vs. 36-41% of depth at first abdominal vertebra vs. in Brachyhypopomus walteri ), more numerous anal fin rays (227-255 vs. 198-216 in Brachyhypopomus walteri ), a deeper electric organ along the body and a short, deep caudal filament (10-19% of LEA vs. 20-32% of LEA in Brachyhypopomus bennetti ) with six bilateral columns of electrocytes at its base (vs. three or four columns in Brachyhypopomus bennetti sp. n.). Subcutaneous pigment suggestive of a teardrop below eye is usually less conspicuous than in the sister species Brachyhypopomus walteri sp. n., although often present. The EOD waveform of B bennetti sp. n. is monophasic in contrast to Brachyhypopomus walteri 's biphasic EOD waveform. Brachyhypopomus walteri sp. n. tends to be less darkly pigmented and more translucent and yellowish in life than Brachyhypopomus bennetti sp. n. Description. Morphometric and meristic data are presented in Tables 2-4. A Brachyhypopomus of moderate adult size for a hypopomid; largest specimen examined measures 232 mm TL, 189 mm LEA. Body very long and compressed, depth at posterior end of abdominal cavity 2.6 to 2.9 times body width. Body more compressed posteriorly, but sides of body with only slight curvature posterior to abdominal cavity. Dorsal profile gently convex. Depth gradually tapers posteriorly: depth of body at 40th post-abdominal vertebra 46-57% of depth at first abdominal vertebra. Head short in comparison to body length, deep and wide: HL 10.3-12.3% LEA, head depth at occiput 76-80% HL, head width at opercle 58-65% HL. Head triangular in lateral view: dorsal profile of head straight from occiput to point of downturn of snout, ventral profile of head straight from lower jaw to opercular area with little if any concavity between opercular area and tip of lower jaw. Eye moderate in size, 11-14% HL. Mouth small, terminal, jaws equal, gape 21-26% HL. Closed lips meet ventral to a horizontal through ventral margin of eye. One or more small needle-like conical teeth present on each premaxilla. This feature is variable, in one case observed only unilaterally. Lower jaw edentate. Maxilla moderate in length, thin, with slight curvature. Snout length moderate, 26-30% HL, edge of upper lip close to farthest anterior extent of snout. Posterior nostril particularly small and close to eye: posterior naris-eye 2.3-4.3% HL. Lateral ethmoids present. Round ossification present in anterior of palatine cartilage. Infraorbital portion of cephalic lateralis system incomplete, lacking recurrent anterodorsal segment and associated pores beneath and anterior to the posterior nares present in most other Brachyhypopomus (see fig. 53 in Sullivan 1997 ); fourth supraorbital pore lying near vertical through posterior nostril, pores inconspicuous. Preopercular lateral-line canal embedded in preopercle, canals radiating out to pores. Pores of lateral-line canal immediately behind head without downward pointing tubes. Discernible lateral scales terminate along caudal filament. Five branchiostegal rays, medialmost two thin compared to outer three, blades oriented nearly vertically. Gill rakers robust for genus, some with weakly ossified cores, on anterior faces of first four gill arches. Rakers subtended on ceratohyals 1-4 by small trough-shaped ossicles. Approximately 50 gill filaments on arch one. Three pectoral radials, with partial fusion of all three at proximal end. Mesocoracoid bridge absent. Pectoral fin broad, robust, 14-17 branched plus unbranched rays, length 5.4-7.5% LEA. Anal-fin rays 227-255, length 4.0-4.5% LEA. Precaudal vertebrae 13-15, a high proportion of specimens show signs of damage and regeneration above anal fin terminus. As many as 72 caudal vertebrae in advance of regenerated portion of caudal filament. Body excluding head and fins covered with thin cycloid scales, small dorsally, larger posterolaterally, partially obscured by skin. Twelve scale rows above, 16 scale rows below lateral line at farthest extent of pectoral fin. Anal-fin origin near vertical through midpoint of extended pectoral fin. Caudal filaments short in intact mature specimens: 10-19% TL. Sexual dimorphism of caudal filaments not noted. Six columns of electrocytes at base of caudal filament, number of columns reduce to three or two along length of filament; 22-35 rows of electrocytes. Electrocytes do not extend anterior to base of urogenital pore. No accessory electric organs on head or humeral region. Figure 6. Holotype of Brachyhypopomus bennetti , INPA 39560 (TL 215 mm, LEA 171 mm), female, Parana do Paracuuba , Amazonas, Brazil. Preserved whole specimen shown above close-up view of specimen immediately post-mortem. Scale bars equals 1 cm. Figure 7. Paratypes of Brachyhypopomus bennetti . A Paratype tag no. 93-214 from INPA 39581 (TL 175 mm, LEA 150 mm), female, Lago Janauari, Amazonas, Brazil B Paratype tag no. 93-137, INPA 8940 (TL 190 mm, LEA 167 mm), Lago Janauari. Preserved whole specimens shown above close-up views of specimens immediately post-mortem. Scale bars equal 1 cm. Table 2. Summary of morphometric measurements for Brachyhypopomus bennetti sp. n. (included are holotype and nine paratypes, identified from radiographs as undamaged at anal-fin terminus).

Measurement	holotype	range	mean	S.D.	N
Proportion of LEA (%)
Proportion of HL (%)

Table 3. Anal-fin ray counts of Brachyhypopomus walteri sp. n. and Brachyhypopomus bennetti sp. n. (holotypes and paratypes) compared to seven other Brachyhypopomus species; modal values highlighted.

Species	170-179	180-189	190-199	200-209	210-219	220-229	230-239	240-249	250-259	260-269	270-279
Brachyhypopomus walteri sp. n.	5
Brachyhypopomus bennetti sp. n.	4
Brachyhypopomus brevirostris	5
Brachyhypopomus bullocki	13
Brachyhypopomus beebei	5
Brachyhypopomus pinnicaudatus	5
Brachyhypopomus occidentalis	2
Brachyhypopomus occidentalis	6
Brachyhypopomus diazi	16
Brachyhypopomus janeiroensis	7

Table 4. Precaudal vertebrae counts of Brachyhypopomus walteri sp. n. and Brachyhypopomus bennetti sp. n. (holotypes and paratypes) compared to seven other Brachyhypopomus species; modal values highlighted.

Species	11	12	13	14	15	16	17	18
Brachyhypopomus walteri sp. n.	5
Brachyhypopomus bennetti sp. n.	5
Brachyhypopomus brevirostris	11
Brachyhypopomus bullocki
Brachyhypopomus beebei	11
Brachyhypopomus pinnicaudatus	20
Brachyhypopomus occidentalis	4
Brachyhypopomus cf. occidentalis	8
Brachyhypopomus diazi	31
Brachyhypopomus janeiroensis	8

Electric organ discharge. The EOD has a simple, head-positive monophasic waveform with a total duration 1.9-2.4 milliseconds at 25°C (Fig. 2). No sexual dimorphism has been observed. Resting EOD rate is very slow (2.0-8.9 Hz, mean 4.7 Hz, median 4.9 Hz, at 21-25° C, n=31). See Appendix III. Coloration. Background color yellowish-tan in life, brownish-tan in preservation. Pigmentation variable: poorly to moderately developed irregular bands along sides, darker and wide above lateral line, often with a spot of darker intensity on lateral line itself. Bands either restricted to anterior portion of body above lateral line or connected to fainter bands below. Some bands connect to 8-12 irregular saddles across dorsum. Saddles more regular in smaller individuals. Dorsal rami of the anterior lateral line nerve visible when viewed from above as two thin, dark parallel lines running along upper back beginning a short distance behind head and continuing to mid-point of the back. Cheeks, underside of head and sides of body below lateral line peppered with prominent dark brown stellate chromatophores that greatly contrast with background color of skin and that do not form part of a larger pattern. Pectoral and anal fins with irregular brown pigment along rays, interradial membranes hyaline. Distribution and ecology. See distribution map, Fig. 5. Brachyhypopomus bennetti sp. n. is known only from Amazon Basin where it appears to be common in floating meadow habitats on the margins of the Amazonas/ Solimoes River and its tributaries. Its distribution and habitat preference seems very similar to that of its sister species, Brachyhypopomus walteri sp. n., with which it is often collected. Etymology . This species is named for Michael V.L. Bennett of the Albert Einstein College of Medicine of Yeshiva University, Bronx, New York, in honor of his pioneering work on electric fish neurophysiology. Bennett (1961 , 1971 ) reported studying a Brachyhypopomus (therein Hypopomus ) with a monophasic EOD likely to have been this species.