Sternarchella schotti (Steindachner, 1868b)

Evans, Kory M., Crampton, William G. R. & Albert, James S., 2017, Taxonomic revision of the deep channel electric fish genus Sternarchella (Teleostei: Gymnotiformes: Apteronotidae), with descriptions of two new species, Neotropical Ichthyology 15 (2), No. e 160168, pp. 1-30 : 24-26

Sternarchella schotti (Steindachner, 1868b)

Fig. 24, Tab. 9

Sternarchus schotti Steindachner, 1868b: 252 , tab. 1, figs. 1-2 [type locality: Brazil, Amazonas , near mouth of río Negro Manaus].

Sternarchus capanemae Steindachner, 1868a: 176 , fig. 1 [type locality: Brazil].

Porotergus terminalis Eigenmann & Allen, 1942:324 [type locality: Peru, río Amazonas , Iquitos].

Sternarchella schotti . - Crampton, Albert, 2006:676, fig. 23.11 [ Brazil, Amazonas, Tefé]. - Crampton, 2007:311, fig. 11.6 [type locality: Brazil, Amazonas, Tefé]. - Lundberg et al., 2013:163, fig. 5 [ Brazil, rio Amazonas above rio Trombetas].

Diagnosis. Sternarchella schotti is readily distinguished from congeners by the presence of a large eye, ED, 7-10% HL (vs. 6-9% HL in S. calhamazon , S. duccis , S. orinoco , S. orthos , S. rex , S. raptor , and S. sima ) (shared with S. patriciae ), the presence of an ossified third basibranchial, the presence of four to five curved displaced hemal spines, and the presence of an elongate swim bladder that extends beyond the posterior limit of the body cavity.

Description. Pectoral fin size small, less than 80% HL. PA% moderate, 46-49% HL. Head width narrow, distance between lateral margins 36-44% HL. Preorbital (snout) length moderate, 30-33% HL. Postorbital distance small, 59-67% HL small. Eye diameter large, 7-10% HL or more. Interorbital distance small, 12-17% HL. Mouth narrow, distance between ricti 16-18% HL. Body depth less than HL. Body translucent in living specimens, yellow or pink hue in living specimens. Scales absent on posterolateral portion of body. Scales large in size with 5-8 present above lateral line at mid-body. Scales dorsal to lateral line rhomboid at mid-body. Rictus extends to a vertical with mental symphysis, gape very small, less than twice eye diameter. Rictus extends to a vertical with mental symphysis. Oral aperture terminal, upper and lower jaws equal in length. Body cavity long; 15-16 pre-caudal vertebrae present. Proximal surface of first displaced hemal spine narrower then descending blade. Four to five curved displaced hemal spines. Swim bladder elongate past posterior limit of body cavity. Anal-fin pterygiophore length longer than hemal spines. Anal-fin proximal long, equal or longer than hemal spine. One row of bones in caudal peduncle visible externally. Caudal peduncle shallow depth 13-24% HL. Dark spot on caudal peduncle absent. No apparent connective tissue between anal-fin base and caudal peduncle. Caudal peduncle length less than HL. Premaxilla size large, lateral margin of premaxilla longer than lateral margin of maxilla. Premaxilla triangular in ventral view. Three rows of teeth present on premaxilla. Anterior hook of maxilla absent, anterior process broad and triangular with a continuous ventral margin with descending blade. Anterior process of maxilla extending as a shelf of bone less than one-third length of descending blade. Ventral margin of maxillary blade curves evenly towards its distal tip. Descending blade maxilla thin, evenly curves. Two rows of teeth present on dentary. Dentary longer than deep, oral margin of dentary longer than length of angular articular. Dorsal margin of dentary slightly concave in lateral view. Posterior margin of dentary curves gradually to descending limb. Endopterygoid process small, not contacting frontal. Endopterygoid process extends vertically at or near a 90º angle with dorsal surface of endopterygoid. Endopterygoid process slender with a narrow tip. Hyomandibula short, its width half its length. Dorsal margin of opercle concave. Opercle broad, width over half depth. Base of gill rakers contacting gill arch. Anterior limb of cleithrum length greater than cleithrum ascending limb length. Post-temporal fused with supracleithrum in mature specimens. Ventral ethmoid large and robust with a large fan-shaped lateral process. Dorso-anterior portion of mesethmoid straight. Anterior tip of mesethmoid scyphate on dorsal surface. Anterior fontanel longer than posterior fontanel. Lateral ethmoid very robust and large, may contact ventral portion on frontals, hour-glass shaped with most narrow portion at mid-length. Orbitosphenoid broad, well ossified in median nasal septum with ventral margin longer than dorsal margin. Dorso-medial portion of orbitosphenoids in contact (visible through anterior fontanel in dorsal view). Process originating from ventral portion of most anterior part of pterosphenoid present, sometimes contacting parasphenoid, anterior ventral margin of pterosphenoid similar to posterior ventral margin of orbitosphenoids. Small, lateral margins of parasphenoid not extending to a horizontal with trigeminal foramen. Parasphenoid ventral margin straight or slightly curved, narrow, just lateral to supraoccipital Parietal ridges are very large and pronounced. Absence of thorny projections at border of parietals and supraoccipital. Dorsal margin of supraoccipital crest exceed dorsal margin of parietals. Supraoccipital crest extends to a dorsal distal tip. Internal carotid foramen reduced. Ventral surface of basioccipital smooth. Anterior extension of infraorbital canal shorter than width of canal pore, anterior canal pore of infraorbital near first infraorbital. Supraorbital canal fused to frontal. Mandibular canal size small. Mandibular canal ossicles form long slender tubes. Supratemporal laterosensory canal curved at a sharp angle on surface of parietal, extending posterior onto epaxial surface of body, terminal canal pore oriented posteriorly, epidermis overlying supratemporal canal depigmented.

Gill rakers long with ossified distal tips. Dorsal surface of basihyal flat; small ridge may be present posteriorly. Second basibranchial fan-shaped, extending to long narrow end. Third basibranchial ossified. Twelve or less teeth present on pharyngobranchial. Eight or more teeth present on sixth hypobranchial. Medial surface of fourth hypobranchial with a process or bridge extending to meet contralateral process on midline. Urohyal blade unossified. First hypohyal bell-or cylinder shaped.

Coloration in alcohol. Yellowish brown color, with a darker brown stripe confined to the dorsum running the length of the body, with striations demarcating the ribs at the body cavity ( Fig. 12b).

Sexual dimorphism. Not known, insufficient mature male and female specimens to determine.

Distribution and habitat. Distributed throughout the deep channels of the Amazon and Orinoco basins. Ivanyisky, Albert (2014) described S. schotti as being restricted to the Amazon basin ( Fig. 17). However, a single juvenile specimen of S. schotti was found inhabiting the río Meta in Colombia, suggesting that S. schotti may have a wider range than originally hypothesized.

Remarks. Sternarchella schotti is readily differentiated from sympatric congeners by the presence of a swim-bladder that extends beyond the posterior margin of the body cavity, visible when held up to a strong light source.

Taxonomic status of Sternarchella terminalis . Sternarchella terminalis ( Eigenmann & Allen, 1942) was originally described as Porotergus terminalis and reassigned to the genus Sternarchella by Mago-Leccia (1994). However, closer examination of the holotype of S. terminalis (IU or CAS 15994), collected near Iquitos, Peru, shows that it possesses the larger eye diameter and distinct configuration of displaced hemal spines that are diagnostic of S. schotti (Steindachner, 1868b; fig. 5). We therefore conclude that S. terminalis (Eigenmann & Allen) is a junior synonym of S. schotti (Steindachner, 1868b) . A species with a similar external phenotype, also present in the Amazon and Orinoco basins, has been incorrectly referred to as S. terminalis in the Amazon previously ( Ivanyisky, Albert, 2014; Lundberg et al., 2013), and was described as S. orthos Mago-Leccia (1994) from the Orinoco basin. Despite measurable morphometric variation among populations of this species in several parts of the Amazon and Orinoco basins, we were unable to discover diagnostic differences among these populations, and here treat the species as S. orthos with a broad geographic range and morphometric variation. A note on the taxonomic status of Sternarchus capanemae was published in Lundberg et al. (2013); here the authors recognize Sternarchus capanemae as a junior synonym of S. schotti .

Material examined. Holotype. Sternarchus schotti: NMW 65335, 1, Brazil, Manaus, mouth of río Negro, F. Steindachner. Nontypes. Sternarchella schotti: ANSP 199195, 4, 117-165 mm LEA, Brazil, río Amazonas above río Trombetas. BMNH 1998.3.17.54, 1, 195 mm TL, Brazil, Mamirauá Lake System, Paraná do Apara: station A, 03º02.52’S 64º51.01’W, 4 Jan 1995. IDSM 494, 1, 212 mm TL, Brazil, río Solimões, south bank of Ilha Içé, 03º16.08’S 64º41.35’W, 3 Sep 1999. INPA 15801, 5, 176-241 mm, Rio Japurá, West bank, between Boca do Lago Mamirauá and Boca do Paraná do Jaquiri, 03º07.58’S 64º47.30’W, 19 Jan 99. INPA 18191, 4, 231-245 mm TL, Brazil, Mamirauá Lake System, Paraná Maiana station A, 03º06.74’S 64°47.53’W, 26 Jan 1999. INPA 18192, 3, 212-233 mm TL, Brazil, río Japurá-Solimões Confluence, Praia Caborini, 03º09.14’S 64º47.06’W, 24 Feb 2000. INPA 18260, 1, 210 mm TL, Brazil, río Japurá, West bank, between Boca do Lago Mamirauá and Boca do Paraná do Jaquiri, 03º07.58’S 64º47.30’W, 9 Feb 1999. INPA 182161, 1, 197 mm TL, Brazil, río Tefé, Toco Preto, 03°47.31’S 64°59.91’W, 23 October 1999. INPA 18262, 1, 159 mm TL, Brazil, Mamirauá Lake System, Paraná Maiana station B, 03º04.83’S 64°47.30’W, 11 Jan 2000. INPA 18263, 3, 128-140 mm TL, Brazil, río Japurá, West bank at Boca do Lago Mamirauá, 03º07.13’S 64º47.30’W, 7 Dec 1999. INPA 18264, 2, 171-187 mm TL, Brazil, río Japurá at mouth of Lago Caxinguba, 03º06.17’S 64º45.84’W, 3 Feb 1999. MCP 33371, 1, 199 mm TL, Brazil, río Japurá, West bank, between Boca do Lago Mamirauá and Boca do Paraná do Jaquiri, 03º07.58’S 64º47.30’W, 19 Jan 1999. MCP 33372, 2, 217-217 mm TL, Brazil, Mamirauá Lake System, Paraná Maiana station A, 03º06.74’S 64°47.53’W, 28 Jan 1999. MCP 33373, 3, 211-222 mm TL, Brazil, río Japurá at mouth of Lago Caxinguba, 03º06.17’S 64º45.84’W, 3 Feb 1999. MCP 33389, 2, 243-244 mm TL, Brazil, río Japurá-Solimões Confluence, Praia Caborini, 03º09.14’S 64º47.06’W, Jan 1999. MCP 49424, 1, 116 mm TL, Brazil, Ponta Mucuri, río Solimões, 03º08’28”S 64º52’00”W, 28 Aug 1993. MCP 49425, 1, 114 mm TL, Brazil, Mamirauá Lake System, Lago Promessa, 03º04’23”S 64°46’52”W, 19 May 1999. MCP 49426, 1, 173 mm TL, Brazil, río Japurá, West bank, between Boca do Lago Mamirauá and Boca do Paraná do Jaquiri, 03º07’35”S 64º47’18”W, 19 Jan 1999. MCP 49427, 1, 132 mm TL, Brazil, río Japurá, West bank at Boca do Lago Mamirauá, 03º07’36”S 64°46’15”W, 7 Dec 1999. MCP 49428, 1, 210mm TL, Brazil, río Solimões, South bank of Ilha Içé, 03º16’05”S 64º41’21”W, 30 Jan 2001. MCP 49429, 10, 150-225 mm TL, Brazil, río Japurá-Solimões Confluence, Praia Caborini, 03º09’08”S 64º47’04”W, 10 Feb 2001. MCP 49430, 1, 166 mm TL, Brazil, río Solimões, South bank of Ilha Içé, 03º16’36”S 64º41’01”W, 13 Jan 2001. MCP 49431, 2, 163-249 mm TL, Brazil, río Solimões near Alvaraes, 03º13’06”S 64º47’01”W, 29 Jan 2001. ZUEC 12339, 4, 179-197 mm TL, Brazil, Mamirauá Lake System, Paraná Maiana station A, 03º06.74’S 64°47.53’W, 2 Mar 1999. Colombia: UF 26079, 1, Colombia, Meta, río Meta, small temporary pond 15 km east of Puerto Gaitán. UF 116570, 1, (C&S), Peru, Maynas, Loreto, río Amazonas, locality unknown. “ Porotergus terminalis”: CAS 52833, 1, 234 LEA, Peru, río Amazonas, Iquitos.