This species is distinguished from its congener in the Upper Amazon by the following set of characters: short supraoccipital spine 0.13-0.17% of SL (vs. typical range between 0.17-0.22% of SL in Serrasalmus but sometimes reaching 0.15 and 0.16 in S. hollandi and S. altispinnis); shallow body 0.45-0.57% of SL (vs. typical body height 0.50-0.62% in Serrasalmus); short dorsal fin, between 0.18-0.20% of SL and 13-15 branched rays (vs. 0.19-0.24% of SL in Serrasalmus); short anal fin, typical 0.32-0.37% of SL with 28-33 branched rays, but overlapping sometimes with other Serrasalmus); adipose fin located on the very posterior part of the body and distant from the dorsal fin end, typically R15 ranging between 0.19-0.22% of SL, but overlapping with other Serrasalmus with R15 ranging between 0.17-0.21% of SL); low number of scales between the lateral line and the dorsal fin, 23.5-29.5 (vs. 28.5-36.5 in other Serrasalmus); an intermediate number of prepelvic serrae 20-24 (Ref. 85594).