Taxonomy & naming
Guyanancistrus teretirostris was described by Fisch-Muller, Mol and Covain in 2018, in a paper revising the systematics of Guiana Shield Ancistrini published in PLoS ONE (volume 13, number 1, e0189789; DOI: 10.1371/journal.pone.0189789). That paper simultaneously revalidated the genus Guyanancistrus — which had previously been synonymised with Pseudancistrus — and described two new species, of which G. teretirostris is one. The holotype is deposited at the Naturhistoriska riksmuseet (NRM) in Stockholm.
The genus Guyanancistrus belongs to tribe Ancistrini within subfamily Hypostominae, family Loricariidae. It is distinguished from Pseudancistrus and other Ancistrini by a combination of characters: evertible cheek plates bearing odontodes are present (distinguishing it from Pseudancistrus), bristle-like odontodes are present on the snout, and the head profile is notably depressed. The genus is restricted to Guiana Shield drainages.
The type locality is a tributary of the Parú de Oeste River in the Sipaliwini-Parú Savannah, Four Brothers (Vier Gebroeders) Mountains, in the Trio Amerindian territory on the Suriname-Brazil border.
Morphology
The maximum recorded standard length of Guyanancistrus teretirostris is 4 in SL, based on the type series. This is a mid-sized Ancistrini — larger than the smallest Ancistrus species but within the range typical for Guiana Shield Ancistrini genera.
The species is characterised by a distinctively rounded, cylindrical snout — the feature directly encoded in the species epithet. The head is notably depressed (flattened dorso-ventrally), a general character of Guyanancistrus that reflects adaptation to life in fast, shallow water over hard substrate. Bristle-like odontodes are present on the snout, and evertible cheek plates bearing odontodes are present, distinguishing the genus from Pseudancistrus. The body is covered in the standard loricariid armour of keeled bony scutes.
Detailed meristic data — precise fin-ray counts, plate row numbers, and morphometric proportions — are documented in the original description (Fisch-Muller et al. 2018, figure 14). Live coloration is documented from holotype photographs at the type locality, showing the typical dark-bodied Ancistrini pattern.
Habitat
All known material of Guyanancistrus teretirostris was collected from a single tributary of the Parú de Oeste River in the Sipaliwini-Parú Savannah, Four Brothers Mountains, at the Suriname-Brazil border. This is one of the more remote and biologically poorly surveyed regions of the Guiana Shield.
The Sipaliwini Savannah is an unusual habitat type for the Guiana Shield — a mosaic of savannah grassland and gallery forest embedded within the broader Amazonian lowland forest matrix, at comparatively low elevation. The rivers and streams of this region drain Precambrian basement rock and are typical Guiana Shield clearwater systems: generally soft, acidic, and well-oxygenated, with rocky substrates in active channels. The Parú de Oeste is a left-bank tributary of the Amazon system, flowing through intact primary forest and protected indigenous territory.
No specific water chemistry or microhabitat data have been published for the collection site.
Feeding
No feeding ecology study has been published for Guyanancistrus teretirostris. The general biology of Ancistrini in Guiana Shield clearwater rivers points toward algivorey and biofilm grazing on rock and stone surfaces in current-exposed microhabitats. The depressed head and suctorial mouth typical of Guyanancistrus are consistent with feeding in fast water over hard substrate, where the fish can maintain contact with epilithic algal mats and diatom films using the ventral surface as a hydrodynamic disc.
The bristle-like snout odontodes, prominent in Guyanancistrus and some related genera, may assist in dislodging periphyton or organic material from rock crevices, though the specific feeding mechanics have not been studied for this species.
Mating
No courtship or mating observations have been published for Guyanancistrus teretirostris. The species was described in 2018, is known from a single remote locality, and has not been kept in captivity. Within Ancistrini broadly, males are typically territorial around nest sites — crevices, cavities, or narrow spaces under boulders — and evertible cheek plates in genera that possess them serve in male signalling and competition.
Guyanancistrus males possess evertible cheek plates with odontodes, suggesting these structures play a role in territorial encounters similar to other Ancistrini. No further reproductive behaviour data are available.
Breeding
No breeding records exist for Guyanancistrus teretirostris in captivity or in the wild. The species is not present in the aquarium hobby.
Cave-spawning with paternal brood care — the reproductive mode documented across most Ancistrini — is the expected strategy by analogy. Under this model, a male would select and defend a rock crevice or overhang, a female would deposit adhesive eggs on the substrate inside, and the male would remain with the clutch through incubation and early larval development, fanning to maintain oxygen flow. Clutch size, incubation duration, and fry development have not been documented for this species.
In the aquarium
Guyanancistrus teretirostris is not present in the aquarium trade and has no registered keepers. No L-number, common name, or hobbyist record is associated with the species. As a 2018 description from an extremely remote and protected locality, it is extremely unlikely to appear in trade in the foreseeable future.
The species is included here for its scientific interest as a recently formalised member of the Guiana Shield Ancistrini fauna. Hobbyists interested in Guianancistrus-type plecos from similar ecological backgrounds can find a small number of related Ancistrini species that do appear occasionally in specialist trade, though most remain poorly represented.
Conservation
The IUCN Red List assessed Guyanancistrus teretirostris as Data Deficient in 2020 (published 2023). The designation reflects the species being known from a single type locality, described only in 2018, with no population data available and no population surveys conducted.
The type locality falls within Trio Amerindian indigenous territory straddling the Suriname-Brazil border — a region of intact primary forest with no road access and very limited human entry. Indigenous land protection currently provides de facto habitat security for the species, but this protection is informal in conservation terms and depends on the maintenance of indigenous land rights rather than formal biodiversity designations.
The IUCN assessment notes that potential threats have not been identified or ruled out. The remoteness of the locality and the protection afforded by indigenous territory status are positive factors, but the Data Deficient assessment appropriately reflects how little is known about the species' actual range, population size, or vulnerability to future pressures. Further collection and survey work across the Parú de Oeste system could clarify whether the species is genuinely range-restricted or simply under-collected.