Pseudochirella fallax is an aetideid calanoid copepod known after both sexes (female 3.60-3.80 mm and male 3.20 mm in length) from the North Atlantic and western part of the Indian Ocean, mainly bathypelagic.
Female. Total length 3.60-3.80 mm. Cephalothorax 4.0-4.6 times longer than abdomen. Rostrum not so well developed as in other species of genus. Th5 posterior corners slightly asymmetrical (dorsal view), prolonged into rounded lobes. Genital segment slightly asymmetrical: lateral swelling on the left is more prominent than right one, genital field is removed laterally (ventral view). Abd1-3 surface with hairs. A1 of about the same length as body. Re1 A2 without setae, Re2 A2 supplied with the distal seta only; Ri1 A2 with 1 seta. Ri1 Md with 2 setae, Ri2 Md with 9 terminal and 2 posterior setae. Second and third Mx1 internal lobes with 5 setae each. Mx2 and Mxp typical of the genus. Re P1 3-segmented. Ri P2 2-segmented. P4 coxopodite with 20-23 spines (Sars, 1925 recorded 14 spines).
Male. Total length 3.20 mm. Cephalothorax about 3.6 times longer than abdomen. Th5 posterior corners without spines, slightly asymmetrical (dorsal view). A1 longer than body by 2-3 last segments. Mx1, Mx2 and setation of other oral parts in comparison with that in females reduced. Re1 and Re2 A2 and Ri1 A2 lacking setae; Ri2 A2 with 5 setae on each lobe. Md palp base with 1 seta, Ri1 Md with 2 small setae, Ri2 Md with 9 terminal setae. Mx1 gnathobase without setae, second and third internal Mx1 lobes with 3 and 5 setae respectively, protopodite near the Ri base with 3 setae, Ri with 12 setae. Re P1 3-segmented, but 1 external spine significantly shorter than in female. Ri P2 2-segmented. P4 coxopodite without spines and setae. Re2 P5 left with 1 tooth. Left Re3 P5 is nearly 4 times longer than wide.
Remarks. The male of the species was mentioned by Sars (1925) only once. Sars recorded its similarity with P. dubia male, but Sars did not describe or figure this male. The male that is described here was obtained in the same sample with female and was attributed to the present species, however its structure is not identical to that of P. dubia male in the understanding of Sars.
Bathypelagic species, was found in hauls in horizontal 1500-2000 m (Deevey and Brooks, 1977), 2000-3000 m (Grice and Hulsemann, 1965), also in total hauls from 1500-4800 m (Sars, 1925) (Markhaseva, 1996).
North Atlantic (Sars, 1925; Grice and Hulsemann, 1965; Wheeler, 1970; Deevey and Brooks, 1977), was recorded for the western part of Indian Ocean (Markhaseva, 1996).
Type locality: The central part of North Atlantic.
1 female and 1 male from sample 399. See examined samples module.