Editorial Type:
Article Category: Research Article
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Online Publication Date: 04 Nov 2022

A New Species of Sternopygus (Gymnotiformes: Sternopygidae) from the Atlantic Coast of the Guiana Shield

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Page Range: 714 – 727
DOI: 10.1643/i2022013
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Sternopygus sabaji, new species, is described from the Atlantic drainages of the Guiana Shield region of South America using traditional methods of morphometrics and meristics and microcomputed tomography (μCT) scans for osteological analysis. The new species is diagnosed from all other species of Sternopygus by the lack of dentition on the anteroventral surface of the endopterygoid and by the possession of a wider mouth. It further differs from its congeners by the following combination of characters: reduced humeral spot with low-contrast and poorly defined margins, possession of a light-colored mid-lateral stripe along posterior portion of lateral line, possession of 1–3 dark saddle-like markings along dorsum of smaller individuals, and a relatively low precaudal vertebrae count. This work provides the first description of a species of Sternopygus that is endemic to the Guiana Shield, joining S. astrabes and S. macrurus in elevating the species richness of the clade in that region to three species and the total number of valid Sternopygus to ten species.

Copyright: © 2022 by the American Society of Ichthyologists and Herpetologists
Fig. 1.
Fig. 1.

Plot of relative head length (%HL) by length from snout to end of anal fin (LEA) showing allometric growth of Sternopygus sabaji. The dashed line indicates the approximate point of the asymptote where specimens are considered to have reached adult body proportions. Only the morphometric values of those specimens to the right of the dashed line were included in Table 3 and the morphometric comparisons in the diagnosis.

Fig. 2.
Fig. 2.

Sternopygus sabaji, holotype, ANSP 208090 (374 mm TL). (A) Full body view; (B) closeup of head. Position of anus and urogenital papilla indicated by arrow. Scale bar = 1 cm.

Fig. 3.
Fig. 3.

Size series comparison of Sternopygus sabaji (ANSP 189018, 208090). Scale bar = 1 cm. Note changes in the proportions of the head, body cavity (coelomic), and tail (post-coelomic) body regions with size.

Fig. 4.
Fig. 4.

Diagram of cephalic sensory canal pore configuration of the head in left lateral view of Sternopygus sabaji, ANSP 189018, 204 mm TL. Lateral sensory pores indicated by circles. Centerline of canals estimated by dashed lines. Anterior and posterior nares shaded gray. Supraorbital (so), infraorbital (io), posterior (pl), preopercular-mandibular (pm), and supratemporal (st) laterosensory canals. so0 indicates the otic canal. Scale bar = 1 cm.

Fig. 5.
Fig. 5.

Comparison of head regions in (A) Sternopygus sabaji ANSP 208090 and (B) Sternopygus macrurus IQ2016 (uncatalogued, collected in Río Nanay drainage near Iquitos, Peru). Scale bar = 1 cm. Note differences in shape of maxilla and dorsal margin of the opercle.

Fig. 6.
Fig. 6.

μCT volume renderings of a sagittal slice taken through the midline of the skull of (A) the holotype of Sternopygus sabaji ANSP 208090 and (B) Sternopygus macrurus IQ2016 (uncatalogued, collected in Río Nanay drainage near Iquitos, Peru). Endopterygoid highlighted in red. White arrow indicates clearly visible mineralized teeth on the ventral surface of the endopterygoid in the 3D rendering of Sternopygus macrurus. Note the lack of mineralized teeth on the ventral surface of the endopterygoid and the flat dorsal profile of the neurocranium in Sternopygus sabaji. Scale bar = 1 cm.

Fig. 7.
Fig. 7.

Sternopygus sabaji neurocranium 3D rendering from μCT scans. (A) Dorsal view; (B) lateral view; (C) ventral view. Scale bar = 1 cm. The enlarged canal bones fused to the frontal and parietal bones of the neurocranium were included in those segments.

Fig. 8.
Fig. 8.

Paratype specimen of Sternopygus sabaji ANSP 189018 (146 mm TL). (A) Specimen with live coloration, photo taken after collection in 2007. (B) Same specimen with preserved coloration photographed in 2021. Scale bar = 1 cm. Photo of specimen with live coloration by Mark Sabaj.

Fig. 9.
Fig. 9.

Lateral view of head and anterior body region two species of Sternopygus from the Guiana Shield. (A) S. sabaji, ANSP 208090; (B) S. sabaji, ANSP 189018; (C) S. macrurus, ANSP 162298; (D) S. macrurus, BMNH 1972.10.17.497-518. Note the larger, broad, darkly pigmented skin patch with high contrast margins in the humeral region of S. macrurus, and the smaller, narrow pigment patch with low contrast margins in the humeral region of S. sabaji.

Fig. 10.
Fig. 10.

Locality collection map of Sternopygus sabaji. All specimens collected in the Atlantic drainages of the Guiana Shield. Collections of S. sabaji indicated by red circles. Type locality marked by star (03°19′31″N, 54°03′48″W), elevation: 111 m. Other lots of Sternopygus macrurus and Sternopygus sp. examined by authors marked by blue circles. Blue square approximates locality of lot from a creek of unknown location within the Approuage drainage, French Guiana. Symbols may represent more than one lot at each locality.

Fig. 11.
Fig. 11.

Photographs of the type locality of Sternopygus sabaji. Specimens were collected at night from undercut banks and small stands of floating vegetation along the shore. Photos by Mark Sabaj taken April 2007.

Contributor Notes

1 University of Louisiana at Lafayette, Department of Biology, Lafayette, Louisiana 70504; Email: (KTT) kevintorgersen@gmail.com; and (JSA) jalbert@louisiana.edu.
Send correspondence to KTT.

Associate Editor: R. E. Reis.

Received: 21 Jan 2022
Accepted: 09 Jul 2022
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