Key to species of Platyrhina from the northwestern Pacific

1 a. 1 row of hooked thorns on mid-dorsum of tail............................................................... 2

1 b. 2 (rarely 3 irregular rows anteriorly) rows of hooked thorns on mid-dorsum of tail........................... P. sinensis

2 a. Hooked thorns on orbital, nape and scapular regions not encircled by light yellow or white pigment (Fig. 2 A–B); a pair of thorns anteriorly on scapular region (Fig. 3 B, indicated by white arrows).................................................................................................. P. hyugaensis Iwatsuki, Miyamoto and Nakaya sp. nov.

2 b. Hooked thorns on orbital, nape and scapular regions encircled by light yellow or white pigment (Fig. 2 C–D); a pair of thorns absent anteriorly on scapular region (Fig. 3 E)........................... P. ta n g i Iwatsuki, Zhang and Nakaya sp. nov.