Somniosus longus is distinguished from S. rostratus in having a relatively longer second dorsal fin where overall length is almost equal to first dorsal fin 91-100% (vs. 76-88%); slightly larger eye with horizontal diameter more than 37% (mean 46%) of length from snout tip to eye (vs. <37, mean 33%); higher number of tooth rows in upper jaw 56-57 (vs.53); and slightly higher spiral valve counts 26-27 (vs. 23 ) (Ref. 50224).