KEY TO THE FAMILIES OF HARPACTICOIDA

(amended from Lang, 1948)

1.	Commensal on whales.	Balaenophilidae ^a)
	Not commensal on whales.	2
2.	Body laterally compressed, as Fig. 4.	Tegastidae
	Body dorso-ventrally compressed, with the expanded epimera of the anterior abdominal segments enfolding the posterior abdomen and caudal furca, giving the body the shape of a wood-louse. (Figs. 5-6).	3
	Body of a different shape from either of above conditions.	4
3.	Body-shape as Fig. 5; without clearly seen chitin “skeleton”; P.1 as Fig. 22.	Porcellidiidae ^a)
	Body-shape as Fig. 6; a chitinous “skeleton” clearly visible; P .1 as Fig. 23.	Peltidiidae
4.	Exp. A.2 of at least 6 segments.	5
	Exp. A.2 of not more than 4 segments.	6
5.	Distal segment of Enp. P.2 much longer than the entire Exp.	Longipediidae ^a)
	Distal segment of Enp. P.2 shorter than the Exp.	Canuellidae
6.	Segment bearing the P.1 not fused to the cph.; Exp. A.2 of 1 segment with several setae; Mxp. lamelliform with several setae. Mosses and freshwaters.	Phyllognathopodidae ^a)
	Segment bearing the P.1 not fused to the cph.; Exp. A.2 of 2 segments; Mxp. not lamelliform. Freshwaters.	Chappuisiidae ^a)
	Segment bearing the P.1 only partially fused with the cph.; Exp. A.2 absent or represented by 1-2 setae only; Mxp. degenerate; Fresh and salt waters.	Darcythompsoniidae
	Segment bearing the P.1 completely fused with the cph.	7
7.	Mx2 as Figs. 13-15; body fusiform or vermiform; Benp. P.5 with only 2 setae (Benp. and Exp. of P.5 may be fused together but the parts are always recognizable) (Fig. 36).	Ectinosomatidae
	These characters not combined.	8
8.	P.1 as Fig. 24.	Harpacticidae
	P.1 as Fig. 25.	Clytemnestridae ^a)
	P.1 as Fig. 26 (Enp. may be 2 or 3 segments).	Tisbidae
	P.1 as Fig. 27.	Tachidiidae
	P.1 as Fig. 28 (Exp. can be 1 to 3 segments; 2nd Enp. segment may bear 1 claw or two long setae); Exp. A.2 present at least as a rudiment.	Laophontidae
	P.1 as Fig. 29; Body pyriform; mouth-organs degenerate.	Metidae
	Exp. P.1 absent or of 1 small segment; Enp. of 2 segments (Figs. 30-31).	Cylindropsyllidae
	P.1 not as any of the above, or, if similar to Fig. 28 then Exp. A.2 absent.	9
9.	Exp. P.1 of 3 segments, middle segment without a spine on the outer border.	10
	Exp. P .1 of 3 segments, middle segment with a spine on outer border or Exp. P.1 of less than 3 segments.	12
10.	Enp. P.2-P.4 of 1 segment; Exp. P.3 (M) modified; 2^nd segment Exp. P.1 without an inner seta.	Parastenocarididae ^a) (freshwater)
	Enp. P.2-P.4 of 1:1:2 segments respectively; Exp. P.3 (M) not modified; 2^nd segment Exp. P.1 without an inner seta.	Cylindropsyllidae
	Enp. P.2-P.4 of 2:1:2 segments respectively; Exp. P.3 (M) not modified; 2^nd segment Exp. P.1 with an inner seta.	Cylindropsyllidae
	Enp. P.2-P.4 each of 2 segments; Exp. P.3 (M) not modified; 2^nd segment Exp. P.1 with or without an inner seta.	11
11.	2^nd segment Exp. P.1 with an inner seta.	Ameiridae
	2^nd segment Exp. P.1 without an inner seta.	Cylindropsyllidae
12.	1^st segment Exp. P.1 with an inner seta; Mxp. not prehensile.	13
	These characters not combined.	14
13.	Exp. A.2 of 1 segment, with at most 2 setae.	Aegisthidae ^a)
	Exp. A.2 of 3-4 segments with several setae.	Cerviniidae
14.	Enp. P.4 at most 2 segments.	15
	Enp. P.4 of 3 segments.	31
15.	Exp. A.2 of 4 segments; Mxp. not prehensile; Enp. P.1-P.4 with 3:2:2:2 segments respectively.	Neobradyidae ^a)
	Exp. A.2 of 3 segments.	16
	Exp. A.2 at most 2 segments.	17
16.	Mxp. not prehensile; Enp. P.1-P.4 with 2:3:2:2 segments respectively.	Tisbidae
	Mxp. prehensile; Enp. P.1-P.4 each of 2 segments.	Diosaccidae
17.	Mxp. not prehensile; A.1 (F) of 5-6 segments with plumose setae, all segments serrated dorsally.	Tisbidae
	Mxp. not prehensile; remainder of above characters not combined.	18
	Mxp. prehensile.	20
18.	P.4 as Fig. 33 (Enp. may be 1 or 2 segments); P.5 a single small plate; A.1 (F) of not more than 7 segments.	Cylindropsyllidae
	These characters not combined.	19
19.	Distal segment Exp. P.2-P.4 with 3 spines on the outer border.	Louriniidae ^a)
	Distal segment Exp. P.2-P.4 with at most 2 setae and/or spines on the outer border.	Darcythompsoniidae
20.	Mxp. as Fig. 20.	Cylindropsyllidae
	Mxp. not as above.	21
21.	Exp. P.4 as Fig. 33 (Enp. may be 1 or 2 segments); P.5 a single plate.	Cylindropsyllidae
	These characters not combined.	22
22.	Mxp. as Fig. 19.	Paramesochridae
	Mxp. not as above.	23
23.	Labrum large and strongly prominent; Rostrum articulated with cph.; Cu.f. always distinctive in shape.	Tetragonicipitidae
	These characters not combined.	24
24.	Exp. A.2 absent; A.1 (F) at most 5 segments.	Ancorabolidae
	These characters not combined.	25
25.	All body segments sharply differentiated; Enp. P.1 not prehensile, at most of 2 segments.	Cletodidae
	These characters not combined.	26
26.	A.1 (F) of 4-5 segments; Enp. P.1 not prehensile.	Cletodidae
	These characters not combined.	27
27.	P.1 as Fig. 32.	Ameiridae
	P.1 not as above; basis of P.2-P.4 transversely prolongated.	Ameiridae
	P.1-P.4 not as either of above.	28
28.	A.2 with basis (Fig. 8).	Ameiridae
	A.2 with allobasis (Fig. 9).	29
29.	Rostrum large; P.5 as Figs. 37-38.	Diosaccidae
	Rostrum large; P.5 not as above; A.1 (F) of 4 segments; Exp. A.2 of 1 segment.	Canthocamptidae
	Not as either above.	30
30.	Enp. P.1 prehensile; Enp. P.2-P.3 of 3 segments.	Diosaccidae
	These characters not combined.	Canthocamptidae
31.	Cuticular lenses present.	Miraciidae ^a)
	No cuticular lenses.	32
32.	Body shape as Fig. 7.	Miraciidae ^a)
	Body shape not as above.	33
33.	A.2 with basis (Fig. 8); Exp. A.2 of 1 segment; Mx2 with at most 3 endites.	34
	These characters not combined.	38
34.	P.5 with Benp. and Exp. distinct.	35
	P.5 with Benp. and Exp. fused to form a single plate.	37
35.	Enp. P.1 of 2 segments, not prehensile.	Cletodidae
	Enp. P.1 of 3 segments.	36
36.	1^st segment Exp. P.1 with an inner seta.	Cletodidae
	1^st segment Exp. P.1 without an inner seta.	Ameiridae
37.	Distal segment Exp. P.2-P.4 each with at least 5 setae and/or spines.	Ameiridae
	Distal segment Exp. P.2-P.4 each with only 4 setae and/or spines.	Latiremidae ^a)
	Distal segment Exp. P.2-P.4 with 4:5:5 setae and/or spines respectively.	Cletodidae
38.	Mxp. well developed, not prehensile.	Tisbidae
	Mxp. not as above.	39
39.	Enp. P.1 not prehensile.	40
	Enp. P.1 prehensile.	43
40.