Sternarchella sima

description

Description. A medium-sized species, to 189 mm LEA. Pectoral fin size large, 80 % HL or greater. PA % small, 24 - 36 % HL. Head width narrow, distance between lateral margins 40 - 49 % HL. Preorbital (snout) length small, 18 - 28 % HL. Postorbital distance large, 64 - 75 % HL. Eye diameter small, 6 - 9 % HL. Interorbital distance large, 19 - 25 % HL. Mouth narrow, distance between ricti 12 - 16 % HL. Body depth equal or greater 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 very small, less than twice eye diameter. Oral aperture sub-terminal, upper jaw extends anteriorly to lower jaw. Body cavity long, 15 precaudal vertebrae. Proximal surface of first displaced hemal spine narrower then descending blade. 1 - 2 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 short, length shorter than hemal spine. One row of bones in caudal peduncle visible externally. Caudal peduncle shallow less

Taxonomic revision of the deep channel electric fish genus Sternarchella (Teleostei: Gymnotiformes: Apteronotidae), with descriptions of two new species

diagnosis

Diagnosis. Sternarchella sima is readily distinguished from congeners by the presence of a short snout (preorbital length 18 - 28 % HL) (vs. 29 - 36 % HL in S. duccis, S. orinoco, S. orthos, S. patriciae, S. raptor, S. rex, and S. schotti) (shared with S. calhamazon), the possession of a large interorbital distance (19 - 25 % HL) (vs. 11 - 19 % HL in S. calhamazon, S. duccis, S. orinoco, S. orthos, S. patriciae, S. raptor, and S. schotti) (shared with S. rex), the possession of a deep body (body depth equal to or greater than HL (vs. shallow body depth, less than HL in S. calhamazon, S. duccis, S. orinoco, S. orthos, S. patriciae, S. raptor, S. schotti) (shared with S. rex), and the presence of gill rakers in which the base does not contact the gill arch (vs. contacting in all other Sternarchella species).

Taxonomic revision of the deep channel electric fish genus Sternarchella (Teleostei: Gymnotiformes: Apteronotidae), with descriptions of two new species

discussion

Remarks. Sternarchella sima superficially resembles, S. orinoco in possessing a sub-terminal mouth, three rows of teeth on the pre-maxilla and dentary, and ventral flexion of the mesethmoid region. However, S. sima is a smaller species, reaching 189 mm LEA (vs. 221 mm in S. orinoco), with a slightly shorter face, pre-orbital length 18 - 28 % HL (vs. 26 - 32 % HL in S. orinoco). Two specimens catalogued as S. sima from the western Amazon are not recognized in this species herein. The paratype of S. sima designated by Starks (1913) described the specimen as having 193 anal-fin rays, here we describe that specimen as possessing 191 anal-fin rays.

Taxonomic revision of the deep channel electric fish genus Sternarchella (Teleostei: Gymnotiformes: Apteronotidae), with descriptions of two new species

distribution

Distribution and habitat. Known from the eastern portion of the lowland Amazon basin, with most specimens known from near its mouth (Fig. 19).

Taxonomic revision of the deep channel electric fish genus Sternarchella (Teleostei: Gymnotiformes: Apteronotidae), with descriptions of two new species