Bradyidius similis is an aetideid calanoid copepod known after both sexes (female 2.84-3.24 mm and male 2.40-2.77 mm in length). Species known off Norwegian coast, the north-eastern Atlantic, the Norwegian and Barents seas.
Female. Total length 2.84-3.24 mm. Cephalothorax 3.2-3.3 times longer than abdomen. Rostrum with slightly divergent rami (in some specimens nearly non divergent). Points of Th5 posterior corners reaching or exceeding the midlength of genital segment. A1 24-segmented, extending about the end of cephalothorax. Re1 A2 lacking setae, Re2 A2 with 2, Ri1 Md with 2, Ri2 Md with 8 terminal setae. Mx1 gnathobase with 4 posterior setae, Ri with 15-17 setae, second internal lobe with 4 (according Shih and Rainville, Maclellan, 1981 with 5), third with 5 (our data with 4) setae, Mx2 and Mxp typical of the genus. External spine at Re1 P1 slightly not exceeding or reaching the base of external spine at Re2 P1, that in its turn exceeds the base of external spine at Re3 P1 - very long, twice as long as its segment. Terminal spines of Re3 P2-P4 with 24 denticles. At Ri P2-P4 there are minute badly visible surface denticles.
Male. Total length 2.40-2.77 mm. Cephalothorax 2.39-2.60 times longer than abdomen. Rostrum with slightly divergent rami. Points of Th5 posterior corners reaching posterior border of Abd1 or exceeding it. Right A1 23-segmented, left 24-segmented, exceeding Th4; penultimate segment of right A1 with a group of denticles. Oral parts in comparison with those in female reduced. External spine at Re1 P1 shorter than in female; P2-P4 as in female. P5 biramous, Ri one-segmented, left Re P5 2-, right 3-segmented.
The species was found near bottom at depth 91-183 m (Sars, 1902) and in total haul from 156 m (Markhaseva, 1996).
Of Norwegian fjords (Sars, 1902), Saguenay fjord and the adjacent St. Lawrence estuary (Shih, Rainville and Maclellan, 1981). North-eastern Atlantic, Norwegian Sea (Vervoort, 1952b), found in the north-eastern part of the Barents Sea (Markhaseva, 1996).
Type locality: Norwegian fjords (Sars, 1902).
2 females and 2 males from sample 458. See examined samples module.