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

We describe <i>Rineloricaria harenae</i> <b>sp. nov</b>., 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 <i>R. harenae</i> 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 <i>Rineloricaria</i> and highlights conservation needs for low-order sandy habitats.