Sternarchella orinoco Mago-Leccia, 1994

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 : 17-19

Sternarchella orinoco Mago-Leccia, 1994

Fig. 18, Tab. 6

Sternarchella orinoco Mago-Leccia, 1994:189 , figs. 94A, B and 95 [type locality: Venezuela, Río Orinoco between km 153 and 152 in front of Isla Iguana, Território Delta Amacuro].

Diagnosis. Sternarchella orinoco can be diagnosed from all congeners by possession of a sub-terminal mouth (vs. terminal or superior in S. calhamazon , S. duccis , S. orinoco , S. orthos , S. raptor , S. rex , and S. schotti ) (shared with S. sima ), the possession of a small interorbital distance, 17-21% HL (vs. 19-25% HL in S. sima ) (shared with S. calhamazon and S. patriciae ) and the presence of a long tail (CPL length more than HL) (vs. 23-93% HL in all other Sternarchella species ).

Description. Pectoral fin size large, 80% HL or greater. PA% small, 32-56% HL. Head wide, distance between lateral margins 37-48% HL. Preorbital (snout) length moderate, 26-32% HL. Postorbital distance large 66-75% HL. Eye diameter small, 5-7% HL. Interorbital distance small, 17-21% HL. Mouth narrow, distance between ricti 15-20% HL. Body depth less than HL. Body color, yellowish gray. 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. Oral aperture sub-terminal, upper jaw extends anteriorly to lower jaw. Body cavity long; 15-16 pre-caudal vertebrae. 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 length, shorter than hemal spine. One row of bones in caudal peduncle visible externally. Caudal peduncle shallow 15-25% HL. Dark spot on caudal peduncle absent. No apparent connective tissue between anal-fin base and caudal peduncle. Tail long, caudal peduncle length greater than HL. Premaxilla large, lateral margin of premaxilla longer than lateral margin of maxilla. Premaxilla square in ventral view. Four 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 curved. Three to four 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 large, contacting frontal. Angle of endopterygoid process with dorsal margin of endopterygoid 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 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 convex and rounded. Anterior fontanel longer than posterior fontanel. Lateral ethmoid large hour-glass shaped, 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. Narrow, just lateral to supraoccipital, parietal ridges are very large and pronounced. No crown of thorny projections present 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. 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. Base of gill rakers contacting gill arch. Gill rakers long with ossified distal tips. Dorsal surface of basihyal convex forming a robust ridge posteriorly. Second basibranchial triangular with short stem (length of descending rod less dorsal margin). Third basibranchial unossified. Fourteen or more 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 triangular, base longer than any other margin of the same bone.

Coloration in alcohol. Yellowish brown color, with striations demarcating the ribs at the body cavity.