Archolaemus janeae, Vari & Santana & Wosiacki, 2012

Vari, Richard P., Santana, Carlos David De & Wosiacki, Wolmar B., 2012, South American electric knifefishes of the genus Archolaemus (Ostariophysi, Gymnotiformes): undetected diversity in a clade of rheophiles, Zoological Journal of the Linnean Society 165 (3), pp. 670-699 : 686-689

ARCHOLAEMUS JANEAE SP. NOV.

( FIGS 5 , 6 ; TABLE 1)

Archolaemus blax, Schwassmann & Carvalho, 1985: 233 , fig. 1 (in part, specimens from Rio Xingu, Belo Monte , Pará, Brazil; not details in species redescription or biological information). Moller, 1995: 451, 455, 453 (illustration, feeding habits). Camargo, Giarrizzo & Isaac, 2004: 139 ( Brazil, lower and middle Rio Xingu). Montag, Freitas, Wosiacki, & Barthem, 2008: 20 ( Brazil, Para, Rio Xingu basin, Floresta Nacional de Caxiuanã).

Diagnosis: Archolaemus janeae is diagnosed from A. blax in the length of the gape (the rictus falling short posteriorly of the vertical through the posterior naris versus extending beyond that line), the form of the premaxilla (the anteroposterior length equal to the transverse width versus the anteroposterior length greater than the transverse width), the distribution of the teeth on the dentary (dentition occupying most of the dorsal margin versus restricted to the anterior one-half or slightly more of the margin), and the number and arrangement of teeth on the internal surface of the endopterygoid (two or three teeth arranged in a single row versus six irregularly distributed teeth). Archolaemus janeae is diagnosed from A. ferreirai by the number of scales above the lateral line at the midbody (15–17 versus 10–14), the form of the premaxilla (the anteroposterior length equal to the transverse width versus the anteroposterior length greater than the transverse width), the distribution of the teeth on the dentary (dentition occupying most of the dorsal margin versus restricted to the anterior one-half or slightly more of the margin), the length of the coronomeckelian bone (less than 20% the length of Meckel’s cartilage versus 50% or more of length of Meckel’s cartilage), and the length of the posterior ceratohyal (1.5 times the length of the ventral hypohyal versus approximately the same size as the ventral hypohyal). Archolaemus janeae is diagnosed from A. luciae in the length of the gape (the rictus falling short posteriorly of the vertical through the posterior naris versus extending beyond that line), the length of the caudal filament (16.0– 25.7% LEA versus 28.6–46.1% LEA), the depth of the caudal filament (5.6–11.2% CL versus 3.3–4.8% CL), the form of the premaxilla (the anteroposterior length equal to the transverse width versus the anteroposterior length greater than the transverse width), the distribution of the teeth on the dentary (dentition occupying most of the dorsal margin versus restricted to the anterior one-half or slightly more of the margin), the length of the coronomeckelian bone (less than 20% the length of Meckel’s cartilage versus 50% or more of the length of Meckel’s cartilage), and the length of the posterior ceratohyal (1.5 times the length of the ventral hypohyal versus approximately the same size as the ventral hypohyal). Archolaemus janeae is diagnosed from A. orientalis by the pigmentation pattern (the presence of a narrow dark stripe along the lateral line and a broad band of dusky to dark pigmentation overlying the basal pterygiophores of the anal fin, versus the lack of such dark pigmentation), the total number of pectoral-fin rays (19–21 versus 16), the total number of anal-fin rays (205–228 versus 164–186), the distribution of the teeth on the dentary (dentition occupying most of the dorsal margin versus restricted to the anterior one-half or slightly more of the margin), and the length of the posterior ceratohyal (1.5 times the length of the ventral hypohyal versus approximately the same size as the ventral hypohyal). Archolaemus janeae is diagnosed from A. santosi by the pigmentation pattern (the presence of a narrow dark stripe along the lateral line and a broad band of dusky to dark pigmentation overlying the basal pterygiophores of the anal fin, versus the lack of such dark pigmentation), the head length at the opercle (13.5–14.7% LEA versus 15.0– 16.3% LEA), the distribution of the teeth on the dentary (dentition occupying most of the dorsal margin versus restricted to the anterior one-half or slightly more of the margin), and the length of the posterior ceratohyal (1.5 times the length of the ventral hypohyal versus approximately the same size as the ventral hypohyal).

Description: Morphometric data for examined specimens of A. janeae are presented in Table 1.

Body elongate and laterally compressed. Greatest body depth located along abdominal cavity or slightly posterior to that region. Body profile very gently convex from rear of head for approximately anterior one-third of body, and then gradually angled posteroventrally along progressively tapering body and caudal filament. Ventral profile of body distinctly convex anteriorly below anterior one-half to twothirds of abdominal cavity, more so in specimens with distended abdomens, and then gradually angled posterodorsally along base of anal fin and caudal filament. Anteriormost perforated lateral line scale located at vertical situated approximately at origin of pectoral fin. Lateral line continuous, extending from immediately after vertical through origin of pectoral fin to end of caudal filament.

Head laterally compressed, widest at opercular region and deepest at nape. Head profile ranging from nearly straight to slightly concave from tip of snout to vertical through orbit, and then straight from that area to rear of head. Ventral profile straight and posteroventrally aligned. Snout subconical, anteroventrally directed and moderately developed. Eye small and located laterally on dorsal one-half of head. Orbital rim partially attached to surface tissues of adjoining region of head in examined specimen of approximately 105 mm TL, but rim totally free and without membrane in larger individuals. Anterior naris located at end of short tube and positioned short distance posterior of tip of snout, but distant from anterior margin of eye. Posterior naris elliptical, without tube and located nearer to tip of snout than to anterior margin of eye. Mouth distinctly inferior, with upper jaw clearly longer than, and overlapping, lower jaw. Gape relatively long, and extending posteriorly beyond vertical through posterior margin of posterior naris. Branchial opening moderately elongate; located along posterior margin of opercle and immediately anterior to anterior margin of pectoralfin origin. Branchial membranes joined at isthmus and extending posteriorly to under pectoral-fin base. Anus proximate to elongate urogenital papilla, and both structures positioned approximately ventral of orbit. Position of anus and urogenital papilla shifting ontogenetically from posterior of vertical through posterior margin of orbit to more anterior position.

Scales small, cycloid, and present from immediately posterior of head to end of caudal filament. Scales along lateral line 146 to 161 (155) (N = 15). Scales above lateral line at midbody 15 to 17 (15) (N = 15). Scales absent on head.

Pectoral fin long, approximately two-thirds of head length, broad, and distally pointed with lateral rays longer. Pectoral-fin rays ii, 19 to ii, 21 (19) rays (N = 15). Anal-fin elongate, extending from vertical through base of pectoral-fin base along most of length of body. Fin margin gently convex anteriorly and then straight for length of fin, but with rays becoming progressively shorter posteriorly. Anal fin with 22–33 (33) unbranched rays (N = 15) and 205–228 total fin rays (220) (N = 9). Caudal filament of moderate length.

Coloration in alcohol: Overall ground body coloration ranging from tan to dark brown. More lightly coloured specimens with pigmentation pattern characteristic of darker specimens less pronounced. More intensely pigmented individuals with overall brown pigmentation more developed dorsally, and narrow dark stripe extending over lateral line from vertical through tip of pectoral fin or slightly posterior of that line to end of caudal filament. Stripe particularly dark in intensely pigmented specimens, such that it stands out even against an overall dark anterior portion of body. Area overlying anal-fin basal pterygiophores with ossifications outlined by variably dark bars on body surface. Bars narrow, distinct, and dusky in overall more lightly coloured specimens, in which they cumulatively form dusky band along ventral portion of body with height of band gradually decreasing posteriorly. More darkly pigmented band in dark specimens quite intense, and individual narrow bars sometimes merge into continuous dark broad band running along ventral portion of body. Dark stripe along lateral line and ventral band overlying basal pterygiophores separated in most specimens by more lightly pigmented, broad midlateral stripe. Lighter stripe less obvious in overall very lightly coloured specimens, and obscured anteriorly in some overall more darkly pigmented individuals. Head ranging from tan ventrally and dusky dorsally in lightly coloured individuals to totally dark brown in large, dark specimens. Smaller darkly pigmented specimens sometimes with lightly coloured area on ventral surface of head. Fleshy covering of branchial opening lightly pigmented, even in dark specimens. Larger specimens in some samples with dark pigmentation patch present immediately anterior to base of pectoral fin. Pectoral and anal fins ranging from hyaline in smaller individuals to dusky in larger specimens.

Coloration in life: (Based on photograph of recently captured specimen from São Felix do Xingu along the Rio Xingu.) Dark coloration overall quite intense, with head, portion of body dorsal of lateral line, and region overlying basal pterygiophores of anal fin nearly black. Rays of anal fin overlain by black pigmentation. Pectoral fin black. Midlateral more lightly pigmented stripe present in most preserved specimens, obscured anteriorly by darker pigmentation that gradually becomes more diffuse posteriorly.

Distribution: Archolaemus janeae is known from the upper and lower portions of the Rio Xingu basin at the Rio Iriri, the Cachoeira de Kaituká at Município de Altamira, and localities in the Rio Culuene, as well as the upper Rio Tapajós basin, where it was collected in the Rio Jamanxim at the Município do Novo Progresso, Brazil ( Fig. 6 ).

Remarks: Two specimens of A. janeae from the Rio Xingu listed by Schwassmann & Carvalho (1985: 233; cited therein as A. blax ) as MPEG 1370 are now registered as MZUSP 31491.

Etymology: The species name, Archolaemus janeae , is in honor of Jane Mertens of Humboldt Universität zu Berlin for her assistance to the second author.

Habitat: The holotype and a portion of the paratype series of A. janeae were collected between 21:00 and 23:00 h in the Rio Iriri, just upriver of a sandbank that separated the tributary from the mainstream Rio Xingu. In this area the river had a pronounced current that was faster towards the centre of the channel, with the substrate in the sampled areas formed by pebbly sand. The depth of the fishing effort varied between <10 cm and about 120 cm, and water parameters at that location were: pH = 5.5; T = 31.1 °C at night and 31.9 °C during the day; dissolved oxygen (D.O.) = 5.9 mg L- 1; conductivity 32.9 uScm-1; and Secchi depth = 187 cm (H. López- Fernández, pers. comm.). Some non-type specimens of A. janeae that originated in the Rio Xingu were captured in the main stream of shallow rapids and small waterfalls, always over a rocky bottom (J.L.O. Birindelli, pers. comm.).

Material examined

Holotype: BRAZIL. Pará: Rio Iriri, just upriver of its mouth into Rio Xingu, Município de Altamira (03°48′54″S, 052°37′09″W), collected by H. López- Fernández, G. Ortí, N. Meliciana, and C. Röepke, 15 August 2008; INPA 30832 (160).

Paratypes: BRAZIL. Pará: collected with holotype, INPA 36380 , 16 (136–225; 2 CS) ; MPEG 21684 , 1 (141) ; USNM 404355 , 1 (191) . Rio Xingu near cachoeira, collected by M. Goulding, 14 October 1983; MZUSP 31491 , 2 (115–206).

Non-type specimens: BRAZIL. Pará: Rio Xingu, Cachoeira de Kaituká, Altamira (03°33′47″S, 51°51′20′W); MZUSP 3930 , 13 (113–340) . Rio Xingu, Furo da Mirandolina (approximately 03°12′43″S, 052°12′12″W); INPA 4131 , 1 (221) . Rio Jamanxim, Rio Tapajós basin, Novo Progresso near Vila Mil (07°43′51″S, 055°16′36″W); MZUSP 97383 , 10 (197– 402) . Rio Jamanxim, Rio Tapajós basin, small beach near Novo Progresso (09°17′59′S, 054°50′00′W); MZUSP 97514 , 9 (213–222) . Rio Iriri (03°48′49″S, 052°38′06″W), MZUSP 105843 , 1 (300) . Rio Xingu, above Belo Monte (approximately 03°17′S, 052°12′W); MZUSP 106054 , 1 (341) . Rio Xingu at Altamira, near Kaituká (03°33′48″S, 051°51′49″W); MZUSP 106223 , 1 (372) . Rio Xingu, Boa Esperança (03°33′44″S, 052°20′59″W); MZUSP 106287 , 1 (only anterior half of specimen) . Rio Xingu, Arroz Crú, Altamira (03°22′05′S, 051°58′02′W); MZUSP 106290 , 1 (209) ; MZUSP 106049 , 1 (230) . Mato Grosso: Rio Xingu basin, Rio Culuene, Paranatinga , cachoeira at site of Pequenia Centrais Hidreléctica Paranatinga II (13°51′08′S, 053°15′22″W); MZUSP 89741 , 3 (191– 232) . Rio Xingu basin, Rio Culuene, Paranantinga , cofferdam of Pequena Centrais Hidreléctica 2 (13°49′00″S, 053°15′00″W); MZUSP 94909 , 6 (253– 368).

Figures

Figure 5. Archolaemus janeae sp. nov., holotype, 160 mm total length, INPA 30832; Brazil, Pará, Rio Iriri, just upriver of its mouth into Rio Xingu, Município de Altamira (03°48′54″S, 052°37′09″W).

Figure 6. Map of lower portion of Amazon basin and adjoining areas, showing geographical distribution of Archolaemus janeae sp. nov. (dots; 1, holotype locality) and Archolaemus luciae sp. nov. (squares; 2, holotype locality) (some symbols represent more than one locality and/or lot of specimens).