Taxonomy & naming
Pareiorhaphis eurycephalus was described by Pereira and Reis in 2002. The parenthetical authority reflects that it was originally placed in a different genus and later transferred to Pareiorhaphis; the Catalog of Fishes (Eschmeyer, CAS) treats the current combination as valid (genus id 34, species id 66831).
The genus Pareiorhaphis belongs to the subfamily Neoplecostominae, a lineage of small, stream-dwelling armoured catfishes concentrated in the coastal and upland drainages of south-eastern and southern Brazil. FishBase still files the genus under Hypoptopomatinae, but the modern systematic literature and the Catalog of Fishes place Pareiorhaphis among the neoplecostomines, which is the classification followed here.
The specific epithet eurycephalus is descriptive, combining the Greek roots eurys (broad) and kephale (head), a reference to the relatively wide head that distinguishes this species.
Morphology
Pareiorhaphis eurycephalus reaches about 2.5 in in standard length (the maximum recorded for a male or unsexed specimen). The body is elongated and clad in the overlapping bony scutes typical of loricariids, with a notably broad head — the feature that gives the species its name. Cleithral width is reported at roughly 33.5 to 40.0 percent of standard length.
The dorsal fin carries about 7 soft rays and the anal fin 5 to 6. As in many neoplecostomines adapted to fast water, the adipose fin is reduced or absent. Detailed published notes on live coloration are sparse; further pattern description is not available from the sources at hand.
Habitat
The species is known from the rio Canoas in Santa Catarina, southern Brazil — part of the upper rio Uruguay system draining the cool highlands of the country's south. It is a tropical freshwater fish recorded as benthopelagic, living close to the bottom in flowing water.
Like other members of the genus, it is associated with rocky, well-oxygenated stream beds where the fish cling to hard surfaces against the current. The genus is noted for facultative air-breathing, an adaptation that buffers these fish against transient drops in dissolved oxygen. Specific published figures for temperature, pH, and depth at the collection sites are not available.
Feeding
No detailed dietary study of Pareiorhaphis eurycephalus is published in the sources at hand. By analogy with its close relatives, which graze the periphyton — the film of algae, diatoms, and associated micro-organisms — coating rocks in their streams, it is reasonable to expect a similar grazing habit, but this should be treated as inference rather than documented fact for this particular species.
Mating
No data on courtship or mating behaviour have been published for this species.
Breeding
No breeding data are available for Pareiorhaphis eurycephalus. Neoplecostomine loricariids generally deposit adhesive eggs on hard substrate and are not commonly bred in aquaria, but nothing specific has been documented for this species.
In the aquarium
Pareiorhaphis eurycephalus is not a species of the ornamental trade and there is no established body of aquarium experience to draw on. Its known requirements — cool, fast-flowing, highly oxygenated upland stream water over rock — make it a demanding subject that would suit only a dedicated biotope set-up rather than a general community tank. No specific captive-care parameters have been published.
Conservation
The IUCN Red List assessed Pareiorhaphis eurycephalus as Least Concern, with the assessment dated 7 November 2018. The species is restricted to the rio Canoas drainage in Santa Catarina but is not presently considered to face significant threats. As with many narrowly distributed upland stream fishes of southern Brazil, the chief long-term concerns would be habitat alteration from land use and hydrological changes within its limited range.