Sternarchella raptor (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 : 22-24

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

Fig. 23, Tab. 8

Magosternarchus raptor Lundberg et al., 1996:658 , fig. 1 [type locality: Amazonas, Brazil, río Solimões, 17 km downriver from confluence of río Purus, 03º36’S 61º21’W, collected using a 3 x 1 m bottom trawl at 4-6 m depth, 29 Nov 1993, J. Lundberg et al.]. - Crampton, 2007:311, fig. 11.6 [type locality: Brazil, Amazonas, Tefé].

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

Diagnosis. Sternarchella raptor can be diagnosed from all congeners by the presence of a long snout, PR 35-38% HL (vs. 24-32 %HL in all other Sternarchella species ), eyes located near the dorsal margin of the head (vs. eyes located on lateral margin of head in S. calhamazon , S. orthos , S. orinoco , S. patriciae , S. rex , S. schotti , and S. sima ) (shared with S. duccis ), a maxilla with an enlarged anterior process greater than one-third the length of the descending blade (vs. reduced anterior process less than one-third the length of descending maxillary blade in all other Sternarchella species ) and robust oral dentition usually visible externally in mature specimens (vs. obscured dentition in S. calhamazon , S. orthos , S. orinoco , S. patriciae , S. schotti , and S. sima ) (shared with S. duccis and S. rex ).

Description. Medium-sized species of Sternarchella , reaching 205 mm LEA. Pectoral fin size small, less than 80% HL. PA% moderate, 39-42% HL. Head width narrow, distance between lateral margins 38-41% HL. Preorbital (snout) length large, 35-38% HL. Postorbital distance small, 58-64% HL. Eye diameter small, 4-7% HL. Interorbital distance small, 10-12% 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 mid-body. Rictus extends to a vertical with mental symphysis, gape short, more than three times eye diameter. Oral aperture terminal, upper and lower jaws equal in length. Body cavity long, 15 precaudal vertebrae. Proximal surface of first displaced hemal spine narrower then descending blade. One to two displaced hemal spines. 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. Caudal peduncle narrow, 14-15% HL. Dark spot on caudal peduncle absent. No apparent connective tissue between anal-fin base and caudal peduncle. Caudal peduncle length short, less than HL. 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 large and broad, extending more than one half length of descending blade in mature specimens. Ventral margin of maxillary blade strait to distal tip. 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° 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 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 strongly curved from anterior tip to frontal boundary. Anterior tip of mesethmoid scyphate on dorsal surface. Posterior fontanel longer than anterior 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. 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 posterior 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 hour-glass shaped with most narrow 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 three male and one female specimens.

Distribution and habitat. Distributed throughout the Amazon basin, where it inhabits deep river channels. ( Fig. 19). Sternarchella raptor is wide-spread in the Amazon basin, however it is often collected in low densities. Gutcontent analysis indicates that S. raptor feeds on the scales and tails of other electric fishes (based on the presence of stacked scales, vertebrae and cartilaginous regenerated caudal filament rods).

Remarks. Sternarchella raptor possesses robust oral and pharyngeal dentition which presumably aid in its predatory feeding habits. This species also possesses the longest snout of any Sternarchella .

Material examined. USNM 337448 , 2 , Brazil, Amazonas, rio Solimões, 6.2 km downriver from confluence with rio Purus , 26 Oct 1993, S. Jewett et al . UF 116762 (1 C&S), Peru, Loreto, Río Amazonas , 28 Mar 2001, J. Albert and W. Crampton . ANSP 200266 , 2, 107-185 mm LEA, Loreto, Río Amazonas, braid off right bank of main channel ca. 6 km northeast (downstream) of mouth of Río Nanay , 03°39’37.3’’S 73°12’16.7’’W, 17 Aug 2015, K. Evans . ANSP 200511 , 3, 169-205 mm LEA, Peru, Loreto, Río Amazonas , 03º42’79”S 073º13’95.2”W, 26 Aug 2016, K. Evans .