Rathbun, 1894
According to Rathbun, the carapace of this species is narrower than that of Achaeus japonicus, being not constricted behind the orbital region; the gastric and branchial regions are smooth, cardiac region mounted with three tubercles, posterior one of which is placed in the median line. The hepatic regions are broad and obtusely produced; the pseudorostral lobes are spinulated on the free margin and separated by a narrow median V-shaped sinus. Eyestalks are distally swollen, armed with an acuminate tubercle on the upper side near the cornea. The abdominal segments of male are all narrow, the terminal segment not being wider than the others.
I have not seen specimens which exactly agree with the characters above enumerated, however, a few specimens of A. japonicus before me have three depressed tubercles on the cardiac region as in this species. (T. Sakai, 1938: 214.)
Type locality: Kanada Bay (= Tokyo Bay?).
Range: Japan - Tokyo Bay ? (Rathbun, 1894b).