Taxonomy & naming
Potamotrygon siponinmorok was described in 2026 by Hemraj-Naraine, Fontenelle, Acosta-Santos, Lovejoy, Liverpool and Kolmann in Neotropical Ichthyology, in a paper devoted to this single new species. It is placed in family Potamotrygonidae, subfamily Potamotrygoninae, order Myliobatiformes — the stingrays.
The holotype, CSBD F3620 (formerly cataloged as ROM 100073, now also ROM T20846), is a juvenile male of 8.82 in disc width, collected from the Demerara River, Guyana (6.543444, -58.243833) in March 2015. Nine paratypes accompany it, eight from the Demerara River and one from 9 mi southwest of the río Guanare, Venezuela. Molecular data (cytochrome oxidase I sequencing across 84 GenBank records, including four individuals of the new species) place P. siponinmorok as a distinct lineage most closely related to P. marinae of the eastern Guianas, P. orbignyi of the Orinoco, and P. schroederi of the rio Negro — material that had previously circulated in the literature as unidentified "Potamotrygon orbignyi ex Demerara River" and "Potamotrygon sp. ex Demerara River". It is diagnosed from these and other regional congeners (P. motoro, P. boesemani, P. schroederi) by a combination of coloration, tooth counts, tooth shape, lateral-line morphology and vertebral count. Catalog of Fishes (Eschmeyer, CAS) is the authority for the valid name used here.
Morphology
The holotype juvenile male of Potamotrygon siponinmorok measured 8.82 in disc width; the largest specimen recorded in the type series, an adult female paratype, reached 13.9 in disc width (roughly 13.8 in), with juveniles as small as 5.04 in DW recorded from Venezuela. The disc is oval, very slightly longer than wide, with small, oval eyes about 1.5 times smaller than the spiracles and a small head making up roughly a fifth of disc length.
The dorsal disc is dark brown, patterned across its medial region with small, light brown rosettes joined into a net-like, hexagonal tracery running from between the eyes to the base of the tail — a pattern that becomes more diffusely reticulate toward the disc margin. A dark, crescent-shaped blotch sits just behind and above each spiracle. The ventral surface is light tan, darkening to gray toward the disc margin and the posterior edge of the pelvic fins, and coloration intensifies in adults. This unspotted, net-like pattern separates P. siponinmorok from the bold, ringed ocelli of P. motoro and P. boesemani and from the rosette clusters of P. schroederi, while its closest look-alikes, P. marinae and P. orbignyi, are distinguished instead by tooth counts and shape, lateral-line canal structure, and a thicker, curved hyomandibular cartilage. Total vertebral count is 131. Like all Potamotrygon, it carries a serrated venomous spine near the base of the tail.
Habitat
Potamotrygon siponinmorok is known from two disjunct localities: the Demerara River drainage of Guyana, where most of the type series was collected, and a single specimen from the río Guanare, part of the Orinoco basin in Venezuela. The describing authors consider two possible explanations for this gap — inland dispersal via the Casiquiare-Negro-Rupununi river corridor that seasonally links the Orinoco and Amazon systems, or coastal dispersal along the Guiana shore during past periods of lower sea level — but note that their genetic data do not clearly support a continuous corridor between the two populations.
Within the Demerara River, the species occupies sandy substrate with minor mud deposits, along banks lined with dense vegetation, predominantly mangrove. Unusually for a freshwater stingray, part of its range lies within the tidally influenced, turbid Demerara estuary: adult P. siponinmorok have been recorded there alongside genuinely marine stingrays, Hypanus geijskesi and H. guttatus, particularly after periods of heavy freshwater outflow, while smaller juveniles are found several miles further upstream, away from the estuary itself.
Feeding
Preliminary stomach-content observations reported in the description indicate that Potamotrygon siponinmorok feeds primarily on aquatic insect larvae and decapod crustaceans, with small fishes taken less frequently — a diet consistent with a benthic ambush predator of sandy, tidally influenced river margins. As in the rest of the family, prey is likely detected through the ampullae of Lorenzini, the electro-sensory pores concentrated on the underside of the disc, which pick up the faint bioelectric signals of animals hidden in the substrate.
This is direct, species-specific evidence rather than a general family-level inference, though the authors describe it as preliminary and based on limited material.
Mating
No courtship or mating behaviour specific to Potamotrygon siponinmorok has been published; the description is based on preserved specimens and genetic material rather than field or captive observation. As in all elasmobranchs, fertilization is internal, with a male gripping a female's disc — typically biting at the margin — and using one of his paired claspers to transfer sperm.
The authors note that males were scored as mature by fully developed, calcified claspers, and that female maturity was estimated using disc-width thresholds established for other, better-studied Potamotrygon species (P. orbignyi, roughly 9.61–10.24 in DW; P. motoro, 12.2–17.32 in DW) as a proxy, since no species-specific maturity threshold has yet been established for P. siponinmorok itself.
Breeding
Potamotrygon siponinmorok is presumed viviparous, as is the whole family Potamotrygonidae, nourishing developing pups after the egg yolk is exhausted through matrotrophic histotrophy — a nutrient-rich uterine secretion the embryos absorb directly. This mode is documented broadly across the family; no litter size, gestation length or other adult reproductive data specific to P. siponinmorok have been published.
The largest individual recorded in the type series, an adult female of 13.9 in disc width from the Demerara River, confirms that the species reaches sexual maturity at a size broadly comparable to other mid-sized Potamotrygon, but details of its breeding biology remain to be documented.
In the aquarium
Potamotrygon siponinmorok is not established in the aquarium trade — it was described only in 2026, and its narrow, disjunct, partly tidal-estuarine distribution makes any wild collection for the hobby difficult to justify, particularly while its conservation status remains unresolved. Genus-level husbandry expectations for Potamotrygon, drawn from better-known aquarium species of similar size, would apply were the species ever to become available: an aquarium measured in square metres of floor space (width and length matter far more than depth), a deep bed of soft, fine sand for a scaleless, burrowing disc easily abraded by sharp substrate, and warm, softly mineralized water maintained with powerful filtration and large, frequent water changes.
As with every Potamotrygon, copper-based medications must never be used, and the serrated venomous tail spine is a genuine medical hazard requiring careful handling and, in many jurisdictions, legal caution. Given how recently this species was recognized and how little is known of its population, only captive-bred stock — should any ever exist — would be appropriate for the trade.
Conservation
Potamotrygon siponinmorok has not been formally assessed by the IUCN Red List; as a species described in 2026 it currently carries no Red List status. The describing authors, applying IUCN criteria informally within their taxonomic paper, recommended a category of Data Deficient, citing the absence of population size and trend data (Criteria A and C) and the lack of a quantitative extinction-risk analysis (Criterion E). This is the describing authors' own proposed assessment, not an official Red List determination.
The species is known from only two drainages — the Demerara in Guyana, based on several specimens, and the río Guanare in Venezuela, based on a single record — a pattern of restricted distribution and few known locations that the authors flag as a conservation concern in its own right. Both areas face anthropogenic pressures including exploratory fishing, boat and shipping traffic, illegal waste disposal and agricultural chemical runoff, though the specific impact of these pressures on P. siponinmorok populations and habitat quality is not yet known. The species is incidentally caught in local fisheries but is not targeted for consumption and is typically released, sometimes after its venomous tail spine is removed. The authors call for further sampling across western Guyana and eastern Venezuela to properly assess the species' area of occupancy and extent of occurrence.