Taxonomy & naming
Guyanancistrus longispinis was described by Heitmans, Nijssen and Isbrücker in 1983 in Bijdragen tot de Dierkunde (volume 53, number 1, page 45, figures 8–9). It was originally placed in the genus Pseudancistrus and has subsequently been moved to Guyanancistrus, the combination recognised by the Catalog of Fishes (Eschmeyer, CAS). FishBase still lists the species under the older combination Pseudancistrus longispinis, so both names appear in the literature for the same fish.
The type locality is the Camopi River at Pauwé Jean-Jean, upstream of Saut Mauvais (approximately 3°11'N, 52°22'W), within the Oyapock River system of French Guiana. The species belongs to the subfamily Hypostominae within the family Loricariidae.
Morphology
Detailed morphometric data for Guyanancistrus longispinis are not readily available in the consulted sources, and a maximum size is not published. As a member of the Hypostominae, it has the overlapping bony body armour and ventral suckermouth typical of the family. Beyond these family-level traits, no reliable description of coloration or distinguishing features can be given here without risk of error — data are sparse.
Habitat
The species is known from the Oyapock River system of French Guiana, with the type material taken from the Camopi River, a tributary of the Oyapock. Recorded water conditions for the fish are acidic and warm: pH around 6.1–6.2 and temperature roughly 77–79 °F, consistent with a tropical, demersal freshwater habitat. No further detail on substrate, current, or seasonal variation is published in the consulted sources.
Feeding
No diet study has been published for Guyanancistrus longispinis. Members of the Hypostominae are typically benthic grazers that rasp algae, biofilm and detritus from hard surfaces, but the specific feeding ecology of this species has not been documented.
Mating
No data published. Courtship and mating behaviour for this species have not been described.
Breeding
No breeding report exists for Guyanancistrus longispinis, in the wild or in captivity. Reproductive mode, clutch size and parental care are all undocumented.
In the aquarium
Guyanancistrus longispinis is not present in the aquarium hobby and there are no husbandry records. Any keeping recommendations would be speculative; the species is known essentially only from scientific collection material.
Conservation
The species has not been evaluated by the IUCN Red List. Its known range is restricted to the Oyapock River system shared between French Guiana and Brazil, but without a formal assessment its conservation status cannot be characterised.