This species is distinguished from P. maderensis and P. nudarcus by having fingerlike papillae along the dorsal margin of the hyoid arch and at the interhyal-posterior ceratohyal articulation, as well as having more dorsal-fin rays (30-33 versus 27-31 in P. maderensis and P. nudarcus) and fewer anal-fin rays (15-18 versus 17-20 in the 2 latter species); Paracaristius aquilus differs from P. nemorosus by its lesser body depth (<50% SL in P. aquilus vs. >50% SL in P. nemorosus) and caudal-peduncle depth (relatively long and shallow in P. aquilus vs. short and deep in P. nemorosus) (Ref. 87954).