A new sand-dwelling species of Rineloricaria (Siluriformes, Loricariidae) from the Eastern Brazilian Basin.

We describe Rineloricaria harenae sp. nov., a sand-dwelling armoured catfish from the Itapocú River, Jaraguá do Sul, Santa Catarina, Brazil. The new species is diagnosed by a distinctive combination of characters: (1) four lateral plate series, with the mid-dorsal series absent; (2) abdomen only partially covered by central plates that do not reach the pectoral-fin insertion; (3) plates of the central abdominal complex arranged in an approximately triangular pattern; (4) cleithral (scapular) region entirely naked or bearing a few small, isolated plates; and (5) presence of five dark transverse bars on the dorsal surface of the body. Mitochondrial COI data corroborate species distinctiveness, and phylogenetic inference under the GTR model recovers R. harenae as a well-supported lineage. The species is currently known only from the type locality, a shallow (< 1 m), sandy reach showing early siltation, suggesting potential vulnerability. Although it exhibits canonical traits of sand-dwelling groups (four lateral plate series, broad naked snout, filamentous upper caudal ray), it differs from sand-dwelling congeners by displaying an abdominal plating pattern typical of rock-dwelling groups. This raises hypotheses about the origin and functional role of ventral plates in Rineloricaria and highlights conservation needs for low-order sandy habitats.