Aetideopsis cristata is an aetideid calanoid copepod known after both sexes (female 3.84 mm in length and male 3.25 mm). The species is known only from Japanese waters.
Female. (Description after Tanaka (1957a) with modifications). Total length 3.84 mm. Cephalothorax 3.26 times longer than abdomen. Points of Th5 posterior corners reaching posterior third of genital segment. Chitin with "dotted structure". Rostrum with robust widely spaced in their base rami. Crest beginning from rostrum (lateral view) and occupies first third of cephalon (dorsal view). A1 reaching distal border of Abd3. Mx2 and Mxp the same as in A. rostrata. External spines at Re1 and Re2 P1 short, not reaching the middle of next joint, at Ri there is small external lobe. Separation between Ri1 and Ri2 P1 incomplete. At Re2 P2-P4 terminal spines 27, 30 and 40 denticles correspondingly.
Male. Total length 3.25 mm. Cephalothorax 2.7 times longer than abdomen. Th4 and Th5 incompletely separated. Points of Th5 corners exceeding posterior border of Abd1. Chitin with "dotted structure". Rostrum with divergent rami with wide base. A1 exceeding posterior border of Th2. Ri and Re A2, also Ri and Re Md of the same length. Mx1 with 2(?) setae at second and third internal lobes, at protopodite near the base of Ri - 4 setae, at Ri - 10 setae, at external lobe - 9 setae. Mx2 strongly reduced, Ri1 Mxp slightly longer than protopodite. P1-P4 as in female. Terminal spines at Re3 P2-P4 with 31, 34 and 36 denticles correspondingly. P5 similar to A. armata figured by Sars.
Species found in vertical total tow from 1000 m (Tanaka, 1957a).
Species known only from the Izu region, Japan (Tanaka, 1957a).
Type locality: the Izu region, Sagami Bay (Tanaka, 1957a).
Species absent in the collections of the Zoological Institute, St. Petersburg.