Schematic representation of the different degrees of proximity between the anal and caudal fins in Heptapterus. a. Keel formed by rigid connective tissue with imbedded ventral procurrent caudal-fin rays not much developed, its anterior end distant from anal-fin base (Heptapterus borodini, H. carmelitanorum and H. hollandi); b. Keel well developed, its anterior end reaching or almost reaching anal-fin base (remaining Heptapterus species).