Taxonomy & naming
Hemiancistrus hammarlundi was described by the Swedish ichthyologist Hialmar Rendahl in 1937, in Arkiv för Zoologi (volume 29, häfte 3 A, number 11). The type material was collected in the Río Clementina system, northwest of Babahoyo in Los Ríos Province, western Ecuador. The Catalog of Fishes (Eschmeyer, CAS) recognises the valid combination Hemiancistrus hammarlundi, and no junior synonyms are currently listed.
The genus Hemiancistrus has long been regarded as a taxonomically problematic assemblage within the tribe Ancistrini of subfamily Hypostominae — a 'catch-all' grouping that has accumulated species not comfortably placed elsewhere. Several species historically assigned to Hemiancistrus have been moved to other genera as the phylogeny of the bristlenose-related loricariids has been refined, and the genus as currently constituted is probably not monophyletic. Whether H. hammarlundi will ultimately remain in Hemiancistrus awaits a focused revision; for now the original combination stands.
Morphology
Hemiancistrus hammarlundi reaches at least 3 in standard length (SL) on the basis of the available material. Like other members of its genus it bears the typical loricariid body plan: a depressed, armoured body covered in rows of overlapping bony scutes, a ventral suckermouth, and an absence of the broad, fleshy snout-edge tentacles seen in the closely related Ancistrus bristlenoses.
Detailed published descriptions of coloration, fin-ray counts, and dentition for this species are sparse, and no comprehensive modern redescription is available. Beyond the size figure and the general genus-level morphology, specific morphometric and meristic data have not been widely reproduced in accessible sources.
Habitat
The species is known from Pacific-slope rivers of western Ecuador, within the Guayas basin — specifically the Río Clementina system in Los Ríos Province. This places it on the western, trans-Andean side of the continental divide, a biogeographically distinct region from the vast Amazon and Orinoco drainages that hold most loricariid diversity. Trans-Andean Pacific-slope rivers tend to support a depauperate but highly endemic fish fauna, isolated from the Amazonian species pool by the Andes.
Published ecological detail — water temperature, pH, substrate, and current preferences — is not available for this species. By analogy with other suckermouth catfishes of the lowland Guayas drainage, it can be inferred to occupy flowing freshwater with submerged hard surfaces, but no field measurements are documented.
Feeding
No feeding study has been published for Hemiancistrus hammarlundi. Members of the genus Hemiancistrus are generally omnivorous grazers, rasping aufwuchs (the biofilm of algae, microorganisms, and detritus) from submerged rocks and wood with their suckermouths, and many take small invertebrates opportunistically. In the absence of species-specific data, only this genus-level generalisation can be offered.
Mating
No data on courtship or mating behaviour have been published for this species.
Breeding
There is no documented breeding report for Hemiancistrus hammarlundi, in the wild or in captivity. Many loricariids of this lineage are cave-spawners with paternal egg care, but this cannot be assumed for H. hammarlundi without observation, and the species is effectively absent from the aquarium trade where such records would normally arise.
In the aquarium
Hemiancistrus hammarlundi is not established in the aquarium hobby. It is not commercially imported, has no L-number designation, and there are no husbandry reports to draw on. Any keeper encountering this species would be doing so as part of a scientific or regional-collection context rather than the ornamental trade, and would need to infer care requirements from better-documented Hemiancistrus and Ancistrini relatives — generally well-oxygenated, clean flowing water, hard surfaces to graze, and shelter among rock or wood.
Conservation
Hemiancistrus hammarlundi has not been evaluated by the IUCN Red List. Its conservation status is therefore formally unknown. As a narrow-range endemic of the Guayas drainage in western Ecuador — a lowland region subject to substantial agricultural conversion, deforestation, and water extraction — it may warrant assessment, but no population data are available on which to base a status. Until a survey establishes its distribution and abundance, any statement about threat level would be speculative.