Sternarchella duccis (Lundberg, Cox Fernandes & Albert, 1996)

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 : 16-17

Sternarchella duccis (Lundberg, Cox Fernandes & Albert, 1996)

Fig. 16, Tab. 5

Magosternarchus duccis Lundberg et al., 1996:664 , fig. 2 [type locality: Roraima, Brazil, rio Branco, 3-11 km upriver from confluence with rio Negro, 1º17’S 61º51’W, collected using a 3 m bottom trawl at 6-7 m depth, 8 Dec 1993, J. Lundberg et al.]. - Crampton, 2007:311: fig. 11.6 [type locality: Brazil, Amazonas, Tefé].

Sternarchella duccis Ferraris et al., 2017:11 [species list].

Diagnosis. Sternarchella duccis can be diagnosed from all congeners by the presence of a highly superior mouth with the lower jaw projecting upwards beyond the upper jaw (vs. terminal in S. calhamazon , S. orthos , S. patriciae , S. raptor , S. rex , and S. schotti and sub-terminal in S. orinoco and S. sima ) and a strongly concave dorsal margin of the frontal (vs. straight in S. calhamazon , S. orthos (western Amazon), S. patriciae , S. raptor , S. rex , and S. schotti and convex in S. orinoco and S. sima ) (shared with Eastern Amazonian populations of S. orthos ).

Description. Medium sized species of Sternarchella reaching an LEA of 266 mm. Pectoral fin size small, less than 80% HL. PA% Moderate, 37-59% HL. Head width narrow, distance between lateral margins 37-42% HL. Preorbital (snout) length moderate, 28-32% HL. Postorbital distance small, 62-71% HL. Eye diameter small, 6-7% HL. Interorbital distance small, 14-15% HL. Mouth wide, distance between ricti 21-25% HL. Body depth less than HL. 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 midbody. Rictus extends to a vertical with mental symphysis, gape short, more than three times eye diameter. Oral aperture superior, lower jaw extends anteriorly to upper jaw. Body cavity long 16 pre-caudal vertebrae present. Proximal surface of first displaced hemal spine narrower then descending blade. One to two displaced hemal spines present. Swim bladder not extending posterior to body cavity. Anal-fin pterygiophore length equal to or shorter than hemal spines. Anal-fin proximal small, shorter than hemal spine. One row of intermuscular bones visible externally in caudal peduncle. Premaxilla large, lateral margin of premaxilla longer than lateral margin of maxilla. Premaxilla triangular in ventral view. Two 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 onethird length of descending blade. Ventral margin of maxillary blade curves evenly towards its distal tip. Descending blade maxilla thin, evenly curved. 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. Endopterygoid process oblique (greater than 90° to with dorsal surface of endopterygoid). Hyomandibula short, its width half its length. Dorsal margin of opercle concave. Opercle broad, width over half depth. Anterior limb of cleithrum length greater than 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. Posterior fontanel longer than anterior fontanel. Lateral ethmoid 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). Absence of ventral process of pterosphenoid, anterior ventral margin of pterosphenoid similar to posterior ventral margin of orbitosphenoids. Lateral process of parasphenoid small, lateral margins of parasphenoid not extending to a horizontal with trigeminal foramen. Parasphenoid ventral margin straight or slightly curved. Distance between parietal ridges narrow, just lateral to supraoccipital, parietal ridges are very large and pronounced. No thorny projections present at border of parietal and supraoccipital. Dorsal margin of supraoccipital crest extends beyond 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 short. 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 posteriorly onto epaxial surface of body, terminal canal pore oriented posteriorly, epidermis overlying supratemporal canal depigmented. Endopterygoid large, contacting frontal. Base of gill rakers contacting gill arch. Gill rakers long with ossified distal tips. Dorsal surface of basihyal flat; small ridge may be present posteriorly. Second basibranchial hourglass shaped with narrowest portion at mid-length. Third basibranchial unossified. 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 white color, with a light brown mid-dorsum along the length of the body.

Sexual dimorphism. No sexual dimorphism found in 2 male and 2 female specimens.

Distribution and habitat. ( Fig. 17). Distributed throughout the Amazon basin, where it inhabits deep river channels, collected at low densities. Gut-content analysis indicates that S. duccis feeds entirely on the tails and scales of other electric fishes.

Remarks. Sternarchella duccis possesses robust oral and pharyngeal dentition, which presumably aid in its predatory feeding habits.

Material examined. ANSP 200270 , 2 , 81-85 mm LEA, Peru, Iquitos, Loreto, Río Nanay, near confluence with Río Amazonas , 03°41’32.9’’S 73°14’32.6’’W, 17 Aug 2015, K. Evans . UF 116561, 1, 215 mm LEA, Iquitos, Loreto, Río Amazonas , 28 Mar 2001, J. Albert, W. Crampton . ANSP 200514 , 3, 209-266 mm LEA, Iquitos, Loreto, Río Amazonas , 03º42’72”S 73º13’95.2”W, 26 Aug 2016, K. Evans . ANSP 192995 (1 C&S), Brazil, Amazonas, rio Solimões, below mouth of Purus , 03º35’51.4”S 61º07’40.8”W, 31 Jul 1996, A. Zanata et al . USNM 337449 (2), Brazil, Roraima, rio Branco, 3-11 km upriver from confluence with rio Negro , 10º16’36”S 61º50’20”W, 8 Dec 1993, J. Lundberg et al .