This species is distinguished from all its congeners, except S. hondoensis and S. undatus, by its predominant 1-2-3-2-2 ID pattern. It also differs from both abovementioned species in having smaller eye (5.3-7.9% HL vs. 11.0-14.9% HL in S. hondoensis and 11.5-13.8% HL in S. undatus). This species further differs from S. hondoensis

in having 9 abdominal vertebrae (vs. 10). S. megasomus is also distinguished from S. undatus, by having higher fin-ray counts, 106-111 dorsal-fin rays and 91-96 anal-fin rays (vs. 101-105 dorsal-fin rays and 87-91 anal-fin rays) and a uniform straw-colored to dark brown ocular-side coloration (vs. freckled ocular-side pigmentation) (Ref. 82423).