和漢三才図会
in his 18th century "Wakan Sansai Zue" stated that the "suiko" was a type/kindred of a "kawatarō" (the western local name for "kappa") but was to be distinguished from it; thus he placed the "suiko" and "kawatarō" as separate (though adjacent) entries. The artist Sekien, who followed after this encyclopedia, also illustrated the two creatures separately.