Phylogenetic relationships among four species of Cyclopsetta and eight species of Syacium were established based on a total of 29 morphological, meristic and osteological characters (CI = 0.75); Citharichthys and Etropus were designated as the outgroups. The Cyclopsetta-Syacium clade was supported by six synapomorphies. Cyclopsetta was strongly supported as monophyletic by ten synapomorphies. This genus was divided into two subgenera, Cyclopsetta comprising C. chittendeni and C. fimbriata and Azevia comprising C. panamensis and C. querna. Syacium was also determined to be monophyletic based on five synapomorphies. S. longidorsale was the first extant species to evolve followed subsequently by S. ovale, S. gunteri, S. maculiferum and a trichotomy containing S. guineensis, S. micrurum and the sister species S. latifrons and S. papillosum.