1	Leg 4 exopod with three segments	2
–	Leg 4 exopod with two segments	4
2	Abdomen more than three times as long as cephalothoracic shield	Caligus bennetti Causey, 1953
–	Abdomen about as long as or slightly longer than cephalothoracic shield	3
3	Inner margin of second exopodal segment of leg 1 with three short setal elements, without postero-lateral process on genital complex	Caligus chorinemi Krøyer, 1863
–	Inner margin of second exopodal segment of leg 1 unarmed; rounded, strongly developed postero-lateral processes on genital complex	Caligus productus Dana, 1852
4	Abdomen one segmented	5
–	Abdomen two or three-segmented	10
5	Abdomen short, about 0.2 times as long as genital complex	Caligus atromaculatus Wilson, 1913
–	Abdomen not as short	6
6	Abdomen about 0.6 times as long as genital complex, without postero-lateral processes on genital complex	7
–	Abdomen as long as genital complex (or even longer), with strongly protruding postero-lateral processes on genital complex	Caligus bonito Wilson, 1905
7	Inner margin of second endopodal segment of leg 2 armed with short, slender setae	8
–	Inner margin of second endopodal segment of leg 2 armed with tooth-like elements	Caligus asperimanus Pearse, 1951
8	Genital complex rugose, with undulate lateral margins	Caligus evelynae sp. n.
–	Genital complex differently built	9
9	Middle two of the terminal elements of leg 1 with accessory process	Caligus rufimaculatus Wilson, 1905
–	Middle two of the terminal elements of leg 1 without accessory process	Caligus constrictus Heller, 1865
10	Abdomen three-segmented	Caligus coryphaenae Steenstrup & Lütken, 1861
–	Abdomen two-segmented	11
11	Claws of leg 4 decreasing in length from the inner to outer margin, inner setae of distal exopodal segment of leg armed with spines	Caligus mutabilis Wilson, 1905
–	Claws of leg 4 with middle and outer elements being equally long and about half the length of inner claw, inner setae of distal exopodal segment of leg setulated	Caligus irritans Heller, 1865