Amynthas hawayana having 70 to 101 body segments. The dorsal body color is reddish-brown or yellowish. It has an epilobic prostomium, and the first dorsal pore typically appears on the 10th or 11th segment. Perichaetine setae are present, with 30 to 49 on preclitellar segments and 48 to 56 on postclitellar segments. The clitellum is annular. Genital markings are postsetal, found in clusters on segments VI-IX and median to male pores, which are superficial on segment XVII. The female pore is usually single and median on segment XIV. Copulatory pouches are absent. Septa 8/9 to 9/10 are aborted, and the intestinal origin is on segment XV. The caeca are simple with short lobes. The typhlosole is rudimentary or absent. It is holandric, with medium to large seminal vesicles. The prostate is globular with a long muscular duct. The spermathecae are medium to large, with a slender duct usually shorter than the ampulla.