Taxonomy & naming
Harttia rhombocephala was described by Alípio de Miranda Ribeiro in 1939 and is recognised as valid by the Catalog of Fishes (Eschmeyer, CAS). It belongs to the subfamily Loricariinae of the armoured catfish family Loricariidae — the elongate, flattened 'whiptail' loricariids — and to the order Siluriformes.
The genus Harttia honours Charles Frederick Hartt (1840–1878), the Canadian-born geologist and naturalist who worked extensively in Brazil. The specific epithet 'rhombocephala' refers to a rhombus- or diamond-shaped head. No L-number or common name is associated with the species.
Morphology
FishBase does not give a maximum length or other size figure for Harttia rhombocephala — size data for the species are sparse. As a member of Harttia and the Loricariinae more broadly, it would have the elongate, dorsoventrally flattened body and slender caudal peduncle ('whiptail') characteristic of the subfamily, with a ventral suckermouth. The epithet points to a head with a diamond-shaped outline, but a full published morphological description is not summarised in the sources available here.
Habitat
Harttia rhombocephala is recorded from the Farias River basin in Brazil. FishBase characterises it as a freshwater, demersal (bottom-dwelling), tropical fish. No specific published data on the water chemistry, current, or substrate of its habitat are available here, though whiptail loricariids of this kind are generally associated with flowing water and sandy or rocky bottoms.
Feeding
No feeding study specific to Harttia rhombocephala has been published. FishBase gives an estimated trophic level of about 2.5, derived from relatives rather than direct study, which is consistent with the omnivorous-to-herbivorous bottom grazing typical of Loricariinae — rasping biofilm, algae, and fine detritus from submerged surfaces. This remains inference from the genus rather than a documented observation.
Mating
No data has been published on courtship or mating behaviour in Harttia rhombocephala.
Breeding
No data has been published on the reproduction of Harttia rhombocephala. Its spawning mode, clutch size, and any parental care remain undocumented in the sources available here. Many Loricariinae are egg-guarders in which the male broods the clutch, but this has not been confirmed for this species.
In the aquarium
Harttia rhombocephala is not a fish of the ornamental trade, and no aquarium husbandry information has been published for it. Any keeping notes would be speculation; it is best treated as a wild taxon known chiefly from scientific records rather than a hobby subject.
Conservation
The IUCN Red List assessed Harttia rhombocephala as Data Deficient (DD) on 7 November 2018, indicating that there is too little information on its distribution, population, and threats to evaluate its extinction risk. Its apparently narrow range in a single river basin means basic field and population research is the priority before any conservation status can be confidently assigned.