Bradyidius angustus is an aetideid calanoid copepod known after male only (total length 1.37 mm). Species recorded from Japanese waters only.
Male. (Description after Tanaka (1957a) with modifications). Total length 1.37 mm. Cephalothorax 3 times longer than abdomen. Rostrum with weakly divergent rami. Points of posterior Th5 corners exceeding the posterior border of Abd1. A1 22(?)-jointed, reaching posterior border of Abd2. External spines at Re P1 short. Ri2-Ri3 P2-P4 with minute spinules on posterior surface. Terminal spines on Re P2-P4 with 22-24, 25 and 27 teeth respectively. P5 uniramous, 4- , 5-jointed, nearly the same in length.
The species was found in total haul from 1000 m (Tanaka, 1957a).
Pacific Ocean: the Izu region (Tanaka, 1957a).
Type locality: the Izu region (Tanaka, 1957a).
Species absent in collections of the Zoological Institute, St. Petersburg.