Hyphessobrycon klausanni sp. n. is described from small drainages of the upper Guaviare River (Orinoco River Basin) in Colombia. It differs from all congeners by having a wide, conspicuous, dark lateral stripe extending from the anterior margin of the eye across the body and continued through the middle caudal-fin rays, and that covers (vertically) three or four horizontal scale rows. It also differs by having an orange-yellow stripe extending from the anterosuperior margin of the eye to the caudal peduncle above the lateral line in life. It differs from all other species of Hyphessobrycon that have a similar dark lateral stripe: H. cyanotaenia, H. loretoensis, H. melanostichos, H. nigricinctus, H. herbertaxelrodi, H. eschwartzae, H. montogoi, H. psittacus, H. metae, H. margitae, H. vanzolinii, and H. peruvianus in having only three or four pored scales in the lateral line, 21 to 24 lateral scales and six teeth in the inner premaxillary row. Hyphessobrycon klausanni differs from H. loretoensis in having seven to eight maxillary teeth (vs. three to four) and in having a longer caudal peduncle (12.4–17.0% SL vs. 4.6–8.0% SL). Additionally Hyphessobrycon klausanni can be distinguished from the other species of Hyphessobrycon with a dark lateral stripe from the Orinoco River Basin (H. metae and H. acaciae) in having two teeth in the outer premaxillary row (vs. three to four) and 10 branched pectoral–fin rays (vs. 11 to 12). It further differs from H. metae by the length of the snout (17.6–22.8% HL vs. 9.9–15.2% HL) and by the length of the caudal peduncle (12.4–17.0% SL vs. 7.3–11.8% SL).
