Taxonomy & naming
Pareiorhaphis parmula was described by Edson H. L. Pereira in 2005, in Neotropical Ichthyology (volume 3, number 2, pages 271–276), from the rio Iguaçu basin in Brazil. The paper is notable for resurrecting the genus Pareiorhaphis Miranda Ribeiro, 1918, and describing this new species within it. The Catalog of Fishes (Eschmeyer, CAS) recognises it as a valid species (spid 68659).
The genus belongs to the subfamily Neoplecostominae within the Loricariidae. (FishBase lists Hypoptopomatinae in its header, a known cataloguing artefact for the genus.)
The specific epithet parmula is Latin for 'small shield,' likely alluding to the small plate on each side of the pectoral girdle that helps diagnose the species.
Morphology
Maximum size for Pareiorhaphis parmula is not reported on FishBase; size data for the species is sparse. The body is described as elongated, in keeping with the slender build of several Pareiorhaphis species.
Two diagnostic features are recorded: a single small plate on each side of the pectoral girdle, just posterior to the gill opening; and, in adult males, a club-shaped pectoral-fin spine that broadens from base to tip. The latter is a clear sexual character — the thickened, club-like pectoral spine of adult males distinguishes them from females, which lack this development.
Habitat
Pareiorhaphis parmula is known from the rio Iguaçu basin in Brazil — a major tributary system of the rio Paraná in the south of the country. It is a freshwater, demersal, tropical species.
No detailed microhabitat description is available in the cached sources beyond these basics. Like other members of the genus, it is a facultative air-breather, a trait typical of loricariids inhabiting warm, fast-flowing or oxygen-variable streams.
Feeding
No diet study for Pareiorhaphis parmula is published in the cached sources. As a loricariid with a ventral suckermouth, it can be presumed to graze biofilm from hard surfaces in the general manner of the family, but its gut contents have not been reported and no specific dietary claim can be made.
Mating
No data on courtship or mating behaviour has been published for Pareiorhaphis parmula. The only sexual character on record is the club-shaped pectoral-fin spine of adult males; no behavioural observations appear in the available sources.
Breeding
No breeding account for Pareiorhaphis parmula exists in the available literature. Spawning mode, clutch size, and parental care are all undocumented, and no claim beyond the general loricariid pattern of male-guarded adhesive eggs would be anything other than speculation.
In the aquarium
Pareiorhaphis parmula is not found in the aquarium trade; it carries no L-number and no husbandry experience has been published. With size data sparse and no documented care history, any husbandry guidance would be pure extrapolation from its rio Iguaçu origin — warm, tropical freshwater — and is not offered here as a recommendation.
Conservation
The IUCN Red List assessed Pareiorhaphis parmula as Least Concern (LC), assessed 7 November 2018. It is not evaluated under CITES, and FishBase rates its resilience as high.
The species occurs in the rio Iguaçu basin, a heavily dammed system in southern Brazil. While its current assessment is Least Concern, the extensive hydroelectric development of the Iguaçu means that long-term monitoring of habitat change would be prudent for the basin's endemic loricariids.