In 1985, Holthuis differentiated P. japonicus from other Parribacus species based on detailed external adult morphology.

[7][6] Ibacinae is one of four subfamilies under family Scyllaridae, which includes all scyllarids or slipper lobsters – clawless decapod crustaceans easily distinguished by their flat and wide plate-like second antennae.

[8][6][7] Nucleotide sequencing and phylogenetic estimations show that P. japonicus is most closely related to P. antarcticus than to other Parribacus species.

[6] The transverse groove, which separates the 20 somites (segments) on the abdomen of P. japonicus, is packed with numerous short hairs.

Additionally, P. japonicus lacks a rostral tooth on its back in comparison to P. scarlatinus, where rostrum is the extension of the anterior carapace margin.

The phyllosoma larva is a transparent, long-legged, leaf-like planktonic zoea; this larval phase lasts for several months.

[8] Various stages of Parribacus phyllosoma larvae have been found to be carried by the Kuroshio Current and countercurrent between Japanese and Taiwanese waters.