Hypopygus minissimus, De Santana & Crampton, 2011

De Santana, Carlos D. & Crampton, William G. R., 2011, Phylogenetic interrelationships, taxonomy, and reductive evolution in the Neotropical electric fish genus Hypopygus (Teleostei, Ostariophysi, Gymnotiformes), Zoological Journal of the Linnean Society 163 (4), pp. 1096-1156 : 1141-1145

HYPOPYGUS MINISSIMUS SP. NOV.

( FIG. 25 ; TABLE 5)

Hypopygus sp. nov. ‘min’. – Crampton & Albert, 2006 [Orinoco basin, list of gymnotiform species]. – Crampton, 2007, table 11.1 [Orinoco basin, list of gymnotiform species].

Diagnosis: Hypopygus minissimus is diagnosed from congeners by the following combination of characters: the absence of oblique bands (versus presence in all congeners), the absence of scales at midbody (versus presence in all congeners), the absence of the sixth infraorbital bone (versus presence in all congeners except H. hoedemani and H. lepturus ), the total number of anal-fin rays (102–113 versus 136–170 in all congeners except H. hoedemani and H. lepturus ), and the dorsal rami of the intermittent branch of the Number of specimens indicated in parentheses. H, holotype; range includes holotypes, paratypes, or nontype specimens. anterior lateral line nerve visible as two black parallel lines (versus not visible in H. ortegai ).

Description: Head and body shape, and pigmentation illustrated in Figure 25 . Morphometric data for examined specimens are presented in Table 5.

Body size exceptionally small, maximum examined TL 64.0 mm (N = 9). Maximum examined length from snout to end of BC 15.8 mm. No sexual dimorphism in body or head shape observed. Snout slightly convex. Upper jaw slightly longer than lower jaw. Pectoral-fin rays 9–11 [11] (N = 5). Postpectoral EO with two columns and four rows of electrocytes. EO dorsal groove extending to approximately two to two and a half orbital diameters before posterior border of eye. Scales absent on mid-dorsal region of body. Scales above lateral line at midbody 3–4 [4] (N = 5). Scales below lateral line 4 [4] (N = 5). Total anal-fin rays 102–113 [105] (N = 5). Caudal filament moderate in length. Precaudal vertebrae 15–16 (12–13 anterior; 2–4 transitional; N = 2).

Pigmentation ( Fig. 25 ): Head and body background coloration uniformly light to dark brown. Pectoral-fin ray, anal-fin ray, and inter-radial membranes hyaline, sporadically speckled with dark chromatophores. Conspicuous absence of oblique bars, spots, or other markings.

Dorsal rami of intermittent branch of anterior lateral line nerve visible as two black parallel lines on each side of upper back, from approximately one to one-half pectoral fin lengths behind the occiput, running posteriorly to mid-dorsal portion of body.

Lateral line nerve visible as dark line, extending from above pectoral fin to approximately two-thirds into caudal filament.

Electric organ discharge: Data available only from four specimens at the type locality. Hypopygus minissimus generates a tetraphasic EOD ( Fig. 17 ) ranging in duration from 0.80 to 1.13 ms (mean 1.00, N = 4), and with a peak power frequency ranging from 2.28 to 2.615 kHz (mean 2.612, N = 4). Mean pulse rate during the day range from 54.1 to 67.1 Hz [mean 60.8, CV 3.59, N = 4], and during the night from 64.1 to 72.3 Hz (mean 69.41, CV 2.04, N = 4).

Distribution: Hypopygus minissimus is known only from the upper Orinoco in Venezuela (vicinity of San Fernando de Atabapo, Río Cunucunuma, and Río Sipapo), and from a tributary of the Casiquiare canal in Venezuela (Río Candela) ( Fig. 26 ).

Ecology: Hypopygus minissimus is known only from small rainforest and savannah creeks. In the vicinity of San Fernando de Atabapo, Amazonas, Venezuela, it is uncommon, and occurs sympatrically with three other Hypopygus species : H. isbruckeri (uncommon), H. lepturus (uncommon), and H. neblinae (common). One stomach content was examined from this species. It contained Chironomidae larvae, and small Coleoptera larvae.

Etymology: The specific epithet, minissimus , is from the superlative of the Latin minimus (smallest), in reference to the status of this species as the smallest known gymnotiform.

Remarks: Hypopygus minissimus possesses four autapomorphies: the loss of the second mandibular canal bone; the loss of the anterior portion of the supraorbital canal; the loss of scales along the mid-dorsal region of body; and the absence of oblique bands on the lateral and dorsal regions of body. It is the smallest member of the genus and the smallest of all known gymnotiforms.

Material examined: (Nine specimens.)

Holotype. Venezuela, Amazonas. UF 175389, WC28.150304, male, 54 mm; Caño Viejita, moriche palm swamp in savannah, road from San Fernando de Atabapo to Santa Bárbara , 16.5 km and 142° from San Fernando de Atabapo , Río Orinoco drainage, 03°55′59.0″N, 067°36′34.2″W; W. Crampton et al., 15.iii.2004.

Paratypes. Venezuela. Amazonas. UF 148533, 5 , 40–62 mm (3 CS) (3 recorded: WC15.120304, female, 44 mm; WC41.120304, female, 42 mm, CS; WC29.150304 , immature, 42 mm, CS); same location as holotype; W. Crampton et al., 12–15.iii.2004 .

Nontypes. MBUCV-V 25679, 1, 62 mm; stream to east of Río Cunucunuma, c. 62 km from Río Orinoco, Río Orinoco drainage, 03°31′42″N, 065°56′45″W; collector not listed, 23.iii.1987. MCNG 21830, 1 male 64 mm; Río Sipapo near Salto Remo, Department of Altures, Río Orinoco drainage, 04°34′28″N, 067°18′31″W; L. Nico et al., 31.v.1989. MCNG 42201, 1 female, 48 mm; Caño Candela near confluence with H. minissimus ), the dorsal rami of intermittent branch of anterior lateral line nerve visible as two black parallel lines (versus not visible in H. ortegai ), the distance from the anus to the anal-fin ray (10.0– 12.0% of LEA versus 7.9–9.4 in H. nijsseni , and 6.5– 9.5 in H. ortegai ), and the number of scales above the lateral line (three to five versus eight to nine in H. isbruckeri ).

Río Pasimoni, Río Candela, Río Casiquiare drainage, 01°32′06″N, 066°34′34″W; L. Nico, H. Jelks, H. López et al., 10.i.1999.

HYPOPYGUS NEBLINAE MAGO- LECCIA

( FIG. 27 ; TABLE 5)

Hypopygus neblinae Mago-Leccia, 1994: 86 , fig. 96 [original description; Venezuela, Amazonas, Río Baría, 3 km downstream of La Neblina base camp, holotype MBUCV-V-14694]. – Provenzano, Marcano & Mondaca, 1998, 11 [listing in type catalogue for MBUCV-V]. – Albert & Crampton, 2003: 495 [in listing of species of the genus; Orinoco basin]. – Crampton & Albert, 2006 [Orinoco basin, list of gymnotiform species]. – Crampton, 2007, table 11.1 [Orinoco basin, list of gymnotiform species].

Diagnosis: Hypopygus neblinae is diagnosed from congeners by the following combination of characters: the total number of anal-fin rays (137–145 versus 102– 135 in H. hoedemani , H. lepturus , and H. minissimus ; 155–174 in H. cryptogenes ), the presence of the sixth infraorbital bone (versus absence in H. hoedemani , H. lepturus , and H. minissimus ), the presence of oblique bands (versus absence in H. minissimus ), the presence of scales at midbody (versus absence in Description: Head and body shape, and pigmentation illustrated in Figure 27 . Morphometric data for examined specimens are presented in Table 5.

Body size moderate, maximum examined TL 119.2 mm (N = 448). Maximum examined length from snout to end of BC 16.2 mm. No sexual dimorphism in body or head shape. Snout blunt. Upper jaw slightly longer than lower jaw. Pectoral-fin rays ten to 11 (N = 9). Postpectoral EO with two columns and five to seven rows of electrocytes. EO dorsal groove extending anteriorly to approximately one orbital diameter behind posterior border of eye. Scales present on mid-dorsal region of body. Scales above lateral line at midbody three to five (N = 9). Scales below lateral line three to five (N = 5). Total anal-fin rays 137–145 (N = 9). Caudal filament moderate. Precaudal vertebrae 15 (12 anterior; three transitional; N = 6).

Pigmentation ( Fig. 27 ): Body background light brown, speckled with dark chromatophores. Clear oblique bands from nape to end of caudal filament. Eighteen to 24 clear bands crossing dorsal region of body, counted from nape to last anal-fin ray. Mid-dorsal portion of body with sparse pale bands. Head light to dark brown, sometimes with a depigmented area at ventroposterior portion to eye. Pectoral-fin ray and inter-radial membrane hyaline, sporadically speckled with dark chromatophores. Prominent and regularly spaced series of V-shaped dark patches at base of anal fin pterygiophores along length of anal fin, extending about one half distance to dorsal edge of pterygiophores. Anal-fin ray and inter-radial membrane hyaline, or lightly speckled with dark chromatophores.

Dorsal rami of intermittent branch of anterior lateral line nerve visible as two black parallel lines on each side of upper back from approximately one to one-half pectoral fin length behind the occiput, running posteriorly to mid-dorsal portion of body.

Lateral line nerve visible as dark line, extending from above pectoral fin to approximately two-thirds into caudal filament.

Electric organ discharge: Data available from near area of type locality, in the area of San Fernando de Atabapo , Amazonas, Venezuela. Hypopygus neblinae generates a tetraphasic EOD ( Fig. 17 ) ranging in duration from 2.109 to 3.443 ms (mean 2.623, N = 24), and with a PPF ranging from 0.715 to 1.359 kHz (mean 1.112, N = 24). Mean pulse rate during the day range from 28.4 to 47.3 Hz (mean 39.5 Hz, CV 4.2 , N = 12) and during the night from 38.6 to 57.2 Hz (mean 46.4, CV 8.04 , N = 8) .

Distribution: Hypopygus neblinae is known from the middle and upper Río Orinoco and the upper Río Meta of Venezuela, the Casiquiare canal of Venezuela, and the Rio Negro and Rio Preto da Eva drainages of Brazil ( Fig. 28 ).

Ecology: In the region of San Fernando de Atabapo, Amazonas, Venezuela, H. neblinae is common in small rainforest and savannah creeks. It occurs in marginal roots, in submerged leaf litter and branches, and in aquatic vegetation. In this region it occurs in sympatry and syntopy with three less common species: H. isbruckeri , H. lepturus , and H. minissimus . Stomach contents (N = 5 examined) contained autochthonous aquatic invertebrates – mostly Chironomidae larvae, small Coleoptera and Ephemeroptera larvae, and unidentified insect parts.

Remarks: The presence of a ventral ethmoid partially fused to the parasphenoid is an autapomorphy for H. neblinae .

Material examined: (448 specimens.)

Brazil. Amazonas. INPA 29934 , 1 , 68.9 mm; PDBFF /km 37, near Manaus, Rio Urubu drainage, 02°24′46″S, 059°46′27″W . INPA 30328 , 1 , 54.3 mm; Igarapé Ajuricaba, near Presidente Figueredo, Rio Urubu drainage, 02°07′04″S, 059°56′06″W . INPA 30725 , 1 , 59 mm; Rio Preto da Eva, Rio Preto da Eva drainage, 02°44′27″S, 059°40′17″W . MPEG 1099 (part), 5, 30–64 mm; Anavilhanas archipelago of Rio Negro, municipality of Novo Airão , Rio Negro drainage, c. 02°44′S, 060°40′W . MPEG 1101 (part), 8, 35–67 mm; Igarapé Tarumã Grande, municipality of Manaus , c. 02°55′S, 060°06′W , Rio Negro drainage. MZUSP 95239 , 2 , 48–69 mm; unnamed lake on margin of Rio Negro, Santa Isabel do Rio Negro , Rio Negro drainage, 00°31′S, 065°01′W . Colombia. Meta. ANSP 128097 , 3 , 62–89 mm; stream entering Lago Mozambique, Mozambique Ranch, Río Meta drainage, Río Orinoco drainage, 03°58′N, 073°04′W . ANSP 128202 , 28 , 45–62 mm; Caño Rico at La Defesa, north-west of Laguna Mozambique, becomes Caño Buenaventura before entering Río Negro, Río Meta , Río Orinoco drainage, 03°59′N, 073°08′W . MPUJ 136 , 6 , 43–88 mm; MPUJ 138 , 6 , 40–43 mm; MPUJ 139 , 2 , 22–25 mm; MPUJ 340 , 1 , 40 mm; MPUJ 343 , 1 , 51 mm; MPUJ 392 , 2 , 27–89 mm; MPUJ 427 , 12 , 51–61 mm; MPUJ 435 , 5 , 31–104 mm; MPUJ 639 , 6 , 37–50 mm; MPUJ 726 , 1 , 42 mm; MPUJ 2497 , 1 , 75 mm; streams in municipality of Puerto Lopez , c. 04°05′N, 072°57′W . Venezuela. Amazonas. AMNH 58648 , 1 , paratype, 76 mm; AMNH 58669 , 3 , paratypes, 63–79 mm; AMNH 58670 , 2 , paratypes, 60–74 mm; Chamuchina, Río Atabapo, Río Orinoco drainage, 03°46′49″N, 067°37′35″W . ANSP 162126 , 1 , paratype, 72 mm; small stream c. 5 km below Raudal Peresa, Río Autana, Río Sipapo, Río Orinoco drainage, 04°46′N, 067°19′W . ANSP 162618 , 4 , 32–63 mm; outflow stream from morichals, c. 5 km from mouth of Río Pamoni, Río Casiquiare drainage. BMNH 2000.4.14.2–3, 2, 59–66 mm; Caño Manu, 250 m upstream of Solano, tributary of Río Casiquiare , Río Casiquiare drainage. FMNH 92567 , 1 , 82 mm; stream 32 km from Puerto Ayacucho on road towards San Mariapo. INHS 44483 , 1 , 69 mm; Caño Topocho, bridge on Puerto Paez- Puerto Ayacucho highway, Río Orinoco drainage, 05°56′41″N, 067°22′08″W . MBUCV-V 12997 , 23 (no size data); MBUCV-V 12998 , paratypes 10 (of 14), 68–74 mm; Rio Atabapo, mouth of stream in front of Ilha Chamuchina. MBUCV-V 14694 , 1 , holotype, 119.2 mm; Río Baria , c. 3 km downstream of Pico Neblina camp, Río Casiquiare drainage, c. 01°28′N, 066°31′W . MBUCV-V 14741 , 79 (no size data); Caño Manu, affluent of Río Casiquiare, c. 250 m upstream of Solano , Río Casiquiare drainage. MCNG 2660 , 2 , 54–57 mm; MCNG 7857 , 1 , 57 mm; Caño Yatuje at end of airstrip, Department of Atures , Río Orinoco drainage, 05°36′22″N, 066°07′15″W . MCNG 3017 , 5 , 36–57 mm; Río Manapiare, near Yutaje, Department of Atures , Río Orinoco drainage, 05°34′60″N, 066°17′50″W . MCNG 6846 , 1 , 68 mm; stream west of Buena Vista, near Río Meta, Río Meta drainage, Río Orinoco drainage, 06°10′20″N, 068°35′50″W . MCNG 21517 , 9 , 25–63 mm; Río Guainia at Maroa, Department of Casiquiare , Río Negro drainage, 02°43′60″N, 067°34′00″W . MCNG 28456 , 1 , 67 mm; Laguna José, c. 4 km upstream of site ′93–4′, Department of Río Negro, Río Yatuá drainage, Río Casiquiare drainage, 01°45′50″N, 066°50′18″W . MCNG 35143 , 4 , 47–79 ; Laguna Cadamuhedeyedi, Río Casiqiuare, Río Casiqiuare drainage, 02.3736°N, 066.5181°W . MCNG 35322 , 1 , 68 mm; Laguna Curamoni, Río Casiquiare , 02°22′25″S, 066°31′52″W . MCNG 38072 , 1 , 69 mm; stream connecting Laguna Cumacapi with Río Siapa, Department of Río Negro , Río Siapa drainage, Río Casiquiare drainage, 01°57′00″N, 066°00′00″W . MCNG 38124 , 3 , 37–57 mm; Caño Buridajow near its confluence with Río Pasimoni, Department of Río Negro , Río Casiquiare drainage. MCNG 42137 , 58 (part), 60–80 mm; Laguna de Candela, bank of Río Pasimoni , headwaters of Río Yatua , Department of Río Negro , Río Casiquiare drainage, 01°31′42″N, 066°33′52″W . MCNG 42200 , 2 , 72–75 mm; Río Candela near confluence with Río Pasimoni, Department of Río Negro , Río Casiquiare drainage, 01°21′18″N, 066°34′34″W . MCNG 26648 (part), 2, 60–70 mm; Caño Topocho on Caicara-Puerto Ayacucho highway, Río Orinoco drainage. MCNG 37945 (part), 3, 58–66 mm; Caño Iguarapo , c. 100 m from confluence with Río Casiquiare , after Piedra Culimacare , Department of Río Negro, Río Casiquiare drainage, 01°58′57″N, 066°45′00″W . UMMZ 228991 , 1 , 66 mm; creek near Puerto Ayacucho. UMMZ 228995 , 1 , 36 mm; UMMZ 230805 , 1 , 30 mm; ‘ El Pozo de Lucas’, 11 km E San Fernando, tributary of Río Orinoco , Río Orinoco drainage, 03°59′23″N, 067°38′15″W . UF 148538, 1 female ( WC19.110304 ), 87 mm; Pozo ‘CVG’ (Corporacion Venezuelana Guyana), on road from San Fernando de Atabapo to Santa Bárbara, 10.5 km and 140° from San Fernando de Atabapo town centre, 03°58′57″N, 067°38′29″W . UF 148540 109, 50– 89 mm (5 CS) (23 recorded: WC11.130304, female 65 mm; WC12.130304, female, 81 mm ( CS); WC13.130304 , female, 49 mm; WC14.130304, female, 74 mm ( CS); WC15.130304 , immature, 80 mm; WC26.150304, immature, 68 mm ( CS); WC27.150304 , immature, 58 mm; 36.150304, female, 77 mm; WC37.150304, immature, 89 mm; WC39.150304, female, 73 mm; WC40.150304, immature 59 mm; WC41.150304, female, 81 mm ( CS); WC42.150304 , female 77 mm; WC43.150304, immature, 73 mm; WC44.150304, male, 82 mm; WC45.150304, immature 78 mm; WC46.150304, immature, 70 mm; WC47.150304, immature, 72 mm; WC48.150304, female, 76 mm ( CS); WC49.150304 , female, 79 mm; WC50.150304, immature, 75 mm; WC51.150304, immature, 71 mm; WC52.150304, immature, 73 mm); Caño Viejita, on road from San Fernando de Atabapo to Santa Bárbara, 16.5 km and 142° from San Fernando de Atabapo, Río Orinoco drainage. Apure. INHS 27708 , 7 , 72–78 mm; Río Cinaruco , on San Fernando to Puerto Paez highway, Río Orinoco drainage, 06°33′06″N, 067°30′43″W . MCNG 26652 , 26 , 27–70 mm; Caño Señor Miguel, just to west of Galeras de Cinaruco, Department of Pedro Camejo , Río Cinaruco drainage, Río Orinoco drainage, 06°34′24″N, 067°17′57″W . MCNG 26697 , 8 , 48–76 mm; lake to west of the Cinaruco highway, Department of Pedro Camejo, Río Cinaruco drainage, Río Orinoco drainage 06°33′06″N, 067°30′43″W . MCNG 28198 , 7 , 39–59 mm; Caño Maporal, Department of Muñoz, Río Apure drainage, Río Orinoco drainage, 07°25′30″N, 069°35′44″W . MCNG 28709 , 4 , 36–52 mm; Módulos de Apure, Department of Muñoz, Río Apure drainage, Río Orinoco drainage, 07°27′10″N, 069°25′15″W . Bolivar. ANSP 162656 , 2 , 47–58 mm; Morichal, Merecure, 3.5 km east of Rio Caura and 1.0 km north of Caicara , Ciudad Bolivar highway, Río Orinoco drainage, 07°25′30″N, 065°10′00″W . ANSP 169660 , 11 , 74–79 mm; Morichal Zamorai (caño) between Río Tauca and Río Tiquire on Maripa-Ciudad Bolivar highway; Río Orinoco drainage, 07°28′N, 064°54′W . CAS-SU 58787 , 1 , 55 mm; CAS-SU 54491 , 1 , 63 mm; Caño de Quiribana, near Caicara. Guarico. MCNG 15997 , 6 , 46–68 mm; Rio Chaviripa at bridge on the Caicara – Puerto Ayacucho highway, Río Orinoco drainage, 07°07′59″N, 066°30′00″W . MCNG 31526 (part), 36, 45–60 mm; Parque Nacional Aguaro-Guariquito, Morichal Charcote, Río San Bartolo , Department of Infante , 08°24′16″N, 066°34′23″W . Country and locality unspecified: USNM 330450 , 2 , 85–96 mm; ‘ South America’ .

Figures

Figure 17. Electric organ discharges (EODs) of Hypopygus as time-voltage waveforms recorded in the far-field. The EODs were in all cases taken from immature specimens or females with adult morphology, and are representative of most individuals of each species (small juveniles and sexually mature males present EODs that in some cases differ from those of larger juveniles, immature adults, and females). A, Hypopygus cryptogenes, INPA uncatalogued, 80 mm (poor signal recording quality). B, Hypopygus isbruckeri, UF 148537 (WC38.150304), immature, 76 mm. C, Hypopygus lepturus, UF 176883 (WC21.090307), female, 92 mm. D, Hypopygus minissimus, UF 148533 (WC41.120304), female, 42 mm. E, Hypopygus neblinae, UF 148540 (WC36.150304), female, 77 mm. F, Hypopygus nijsseni MCP 44740 (WC01.070703), immature, 70 mm. G, Hypopygus ortegai, MUSM 35305, holotype (WC02.160104), female, 107 mm. Scale bars = 1 ms. Dashed horizontal line = 0 volts. Note that all species generate EODs with a similar four- or five-phase structure, with minimal interspecific variation in duration (except in H. neblinae where the EOD is clearly longer).

Figure 25. Hypopygus minissimus, holotype, head, and lateral and dorsal views of body. UF 175389 (WC28.150304), male, 54 mm; Venezuela, Caño Viejita, on road from San Fernando de Atabapo to Santa Bárbara, 16.5 km and 142° from San Fernando de Atabapo, Río Orinoco drainage. Scale bars = 5 mm. Tissue removed from right flank.

Figure 26. Map of northern South America showing collection records of Hypopygus minissimus. Some symbols represent more than one nearby collecting locality.

Figure 27. Hypopygus neblinae, nontype, head, and lateral and dorsal views of body. UF 148540 (WC49.150304), female, 78 mm: Venezuela, Caño Viejita, on road from San Fernando de Atabapo to Santa Bárbara, 16.5 km and 142° from San Fernando de Atabapo town centre, Río Orinoco drainage. Scale bars = 5 mm.

Figure 28. Map of northern South America showing collection records of Hypopygus neblinae (circles), Hypopygus nijsseni (squares), and Hypopygus ortegai (triangles). Some symbols represent more than one nearby collecting locality.