Taxonomy & naming
This species was described by Lujan and Armbruster in 2011, in the paper 'Two new genera and species of Ancistrini (Siluriformes: Loricariidae) from the Western Guiana Shield,' published in Copeia (2011, issue 2, pages 216–225). It was originally placed in a newly erected, monotypic genus, Soromonichthys — that is, a genus created to hold this single species — with the original combination Soromonichthys stearleyi. The valid combination is now Pseudolithoxus stearleyi: FishBase treats the species within Pseudolithoxus, so the genus name attributed to Soromonichthys is retained as a synonym while the species is referred to the older, broader genus. Both names refer to the same fish; the change reflects a reassessment of where this small ancistrin belongs rather than the discovery of a new population.
The species sits in the family Loricariidae, subfamily Hypostominae, tribe Ancistrini — the group of bristlenose-type armoured catfishes. The type material comes from Soromoni Creek in Amazonas State, Venezuela, on the western Guiana Shield, in the upper Orinoco region near the Casiquiare drainage.
The genus name Soromonichthys was formed from the type-locality creek, Soromoni, combined with the Greek 'ichthys' (fish). The species epithet 'stearleyi' honours Ralph F. Stearley, professor of geology and palaeontology at Calvin College, who tutored the first author in fish osteology.
Morphology
Pseudolithoxus stearleyi is a dwarf loricariid: the type series reaches only about 1 in standard length, making it one of the smallest suckermouth catfishes on record. As an ancistrin it carries the family's armour of overlapping bony plates and the ventral, rasping suckermouth.
Its colour pattern is distinctive: thin, irregular light-yellow to gold bars over a base of mixed moderate-to-dark green. The dorsal fin bears seven rays. The original description diagnosed the species in part by a unique pattern of plate loss on the snout — a reduction in the bony covering at the front of the head that distinguishes it from related ancistrins.
No data on sexual dimorphism in this species has been published. Many ancistrins develop cheek and snout odontodes that differ between the sexes, but specific observations for P. stearleyi are not available.
Habitat
The species is known from Soromoni Creek in Amazonas State, Venezuela, on the western Guiana Shield — an upper-Orinoco / Casiquiare-region drainage at roughly 3–4°N, 65–66°W. It is a freshwater, demersal (bottom-dwelling), tropical fish.
The original collections describe it from shallow riffles and runs over clean cobble substrate, interspersed with sand and with patches of rooted, moss-like aquatic macrophytes. This is a clear, well-oxygenated, fast-water habitat rather than a slow forest pool. Loricariids found living alongside it in Soromoni Creek include an Ancistrus species, Dekeyseria niveata, an Exastilithoxus species, and Rineloricaria formosa.
No measured water-chemistry values (temperature, pH, hardness) for the type locality are published in the available sources.
Feeding
No feeding study specific to Pseudolithoxus stearleyi has been published. Like other small ancistrins of fast, rocky creeks, it would be expected to rasp biofilm — algae, micro-organisms, and fine detritus — from the surfaces of cobbles and submerged macrophytes using its suckermouth. In the absence of direct dietary data, this remains inference from habitat and from the feeding habits of related fishes rather than a documented account.
Mating
No data on the courtship or mating behaviour of this species has been published. It has not been recorded breeding in aquaria, and no field observations of reproduction are available in the sources consulted.
Breeding
No breeding data exists for Pseudolithoxus stearleyi. Many ancistrins are cave-spawners with paternal egg care, but there are no published clutch sizes, spawning sites, or developmental observations for this species, and it is not established in the aquarium hobby.
In the aquarium
Pseudolithoxus stearleyi is essentially unknown in the aquarium hobby. PlanetCatfish carries no Cat-eLog entry for it, and no L-number has been assigned. Husbandry data is sparse to non-existent.
No specific care recommendations can be made responsibly from published sources. Any keeper encountering the species would have to reason from its natural habitat — shallow, fast, well-oxygenated water over clean cobble — rather than from an established body of aquarium experience. Given its tiny adult size and riffle-dwelling habits, it would be a specialist's fish rather than a community subject, but this should be read as inference, not documented practice.
Conservation
The IUCN Red List assessed Pseudolithoxus stearleyi as Data Deficient (DD) on 5 June 2017. A Data Deficient listing means there is not enough information on the species' distribution, population, or threats to judge its risk of extinction — not that it is necessarily secure. The assessment was made on the basis of the known range in Soromoni Creek, Venezuela.
With a single known locality on the western Guiana Shield and very little biological information available, the species' status is genuinely uncertain. Targeted survey work would be needed before any threat category could be assigned with confidence.