Atlantirivulus maricensis can be diagnosed from all other species of the genus Atlantirivulus by the following combination of characters: lateral line divided into two sections (vs. single); lateral line with one neuromast by scale (vs. lateral line often interrupted by scales without neuromasts); scales in the longitudinal series 33-35 (vs. 30-31); vertebrae 33-24 (vs. 31-32); caudal fin with 30-31 rays (vs. 25 - 29); small, horizontally elongated black spot on dorsal portion of caudal-fin base in females, not contacting fin margin (vs. female caudal spot never horizontally elongated, often triangular or rectangular, reaching fin margin, sometimes spot absent); flank with horizontal rows of red dots in males and small light brown spots in females (vs. never a similar color pattern, red pigmentation when present often forming irregular bars or reticulations in males); caudal fin in males greenish yellow, sub-dorsal and sub-ventral portions bright yellow, dorsal and marginal region diffuse orangish grey, posterior marginal portion diffuse pale greyish yellow (vs. never a similar color pattern); small red spots on the basal and posterior portions of the dorsal fin in males (vs. red spots absent).