1a |
a. Head produced anteriorly as a rostrum |
Curculionidae |
b. Tarsal formula 4-4-4 |
c. Antenna geniculate |
1b |
a. Head not produced as a rostrum |
2 |
b. Tarsal formula variable |
c. Antenna not geniculate |
|
2a(1b) |
a. Compound eyes divided into separate dorsal and ventral segments |
Gyrinidae |
b. Ant2 elongate and scoop-shaped |
c. Meso- and metathoracic legs short, flattened |
d. Tarsi folding fan-wise |
2b |
a. Compound eyes undivided |
3 |
b. Ant2 variable but without a scoop-shaped Ant2 |
c. Meso- and metathoracic legs not extremely flattened |
d. Tarsi not folding fan-wise |
|
3a(2b) |
a. Elytra truncate, exposing at least 2 entire abdominal tergites |
Staphylinidae |
also: Riparian, semi- or periaquatic |
3b |
a. Elytra covering the entire abdomen, or only part of the last abdominal tergite is exposed |
4 |
|
4a(3b) |
a. Hind coxae expanded as broad, flattened plates covering covering 2 or 3 basal abdominal segments and concealing all but apices of hind femora |
Haliplidae |
4b |
a. Hind coxae sometimes extending posteriorly along midline, but never as broad plates |
5 |
|
5a(4b) |
a. Hind coxae with medial portion extending posteriorly to divide 1st abdominal sternite into lateral sclerites |
6 |
b. Prothorax with distinct notopleural sutures |
5b |
a. Hind coxae not extending posteriorly to divide 1st abdominal sternite |
10 |
b. Notopleural sutures almost always absent |
|
6a(4a) |
a. Hind tibiae and tarsi cylindrical or subcylindrical in cross section, without long, stiff swimming bristles |
Carabidae, terrestrial, accidental to aquatic environments, not keyed further |
also: Elytra bearing several long, slender, erect sensory hairs |
6b |
a. Hind tarsi and usually tibiae flattened, streamlined, and bearing long, stiff swimming bristles |
7 |
|
7a(6b) |
a. Ventral surface of body in lateral aspect with anterior of prosternum greatly depressed and much more dorsal than its postcoxal process and meso- and metasternum |
Dytiscidae (in part), Hydroporinae |
b. Pro- and mesotarsi appear to be 4-segmented because segment 4 is very small, concealed between lobes of segment 3, and much shorter than segments 3 or 5 (except Bidessonotus) |
7b |
a. Ventral surface of body in lateral aspect with anterior of prosternum, its postcoxal process (prosternal process), and meso- and metasterrnum in same plane |
8 |
b. Pro- and mesotarsi distinctly 5-segmented, segment 4 as long as segment 3 |
|
8a(7b) |
a. Prosternal process spear-shaped, usually pointed apically |
Dytiscidae (in part) |
b. Protibia without a large, curved, apical spur |
8b |
a. Prostemal process greatly widened apically and nearly truncate |
Noteridae |
b. Protibia with a large, curved spur at apex |
|
10a(5b) |
a. Antennae with terminal segment no longer than combined length of 2 preceding segments |
11 |
also: Terminal segments may be fused into a globular or elongate club |
10b |
a. Antennae with terminal segment as long as combined length of 3-4 preceding segments |
12 |
|
11a(10a) |
a. Antennae terminating in abrupt, globular or elongate club |
12 |
also: Antennae with 2nd segment attached apically on 1st; antennal club consisting of 2-5 articulated segments |
11b |
a. Antennae slender, elongate or very short, thick, with basal segment enlarged |
16 |
|
12a(10a, 11a) |
b. Antennal club with 5 segments |
Hydraenidae |
a. Abdomen with 6-7 visible sternites |
12b |
a. Abdomen with 5-6 visible sternites |
13 |
b. Antennal club with 3 segments |
|
13a(12b) |
a. Pronotum projected forward, totally or partly covering the head |
Georissidae, Georissus pusillus LeConte |
b. Tarsomere1 of proleg very small (tarsi pseudotetramerous), foretarsi appearing as having 4 segments |
c. Metacoxae widely separated, intercoxal process broadly truncate |
d. Very small beetles, < 2.2 mm, body strongly convex |
also: Semiterrestrial, in damp soil along water edges |
13b |
a. Pronotum not, or only slightly, projected forward, not or only slightly covering the head |
14 |
b. Tarsomere1 of proleg not markedly reduced in size, foretarsi clearly with 5 segments |
b. Metacoxae nearly contiguous, intercoxal process narrow |
c. Shape variable |
|
14a(13b) |
a. Pronotum bearing five well-developed longitudinal grooves |
Helophoridae, Helophorus |
14b |
a. Pronotum lacking strongly impressed longitudinal grooves |
15 |
|
15a(14b) |
a. Pronotum distinctly narrower than the elytral base |
Hydrochidae, Hydrochus |
b. Overall body form narrow and elongate |
c. Antennae before club with 4 glabrous antennomeres |
d. Meso- and metatibiae lacking natatory setae |
e. Elytra with strongly impressed sculpture, often encrusted with dirt |
f. Small beetles, length < 5 mm |
15b |
a. Pronotum not distinctly narrower than the elytral base |
Hydrophilidae |
b. Body form generally not as above |
c. Antennae before club with 5-6 glabrous antennomeres, if only 4, then meso- and metatibiae bearing long natatory setae |
d. See c |
e. Elytra generally smooth or with moderate sculpture |
f. Size variable |
|
16a(11b) |
a. Tarsal formula 4-4-4 |
Chrysomelidae |
also: Antennae thickened apically, longer than head and thorax; mandibles smalI, directed ventralIy |
16b |
a. Tarsal formula 5-5-5 |
17 |
|
17(16b) |
a. Abdomen with at least 8 visible sternites |
Lampyridae |
17b |
a. Abdomen with 5-7 visible sternites |
18 |
|
18a(17b) |
a. Prosternum expanded anteriorly as prominent lobe beneath head, head usually contracted into thorax concealing antennae and eyes |
19 |
18b |
a. Prosternum not markedly expanded anteriorly beneath bead, antennae clearly visible |
22 |
|
19a(18a) |
a. Antennae usually thick, with enlarged basal segment, about as long as head |
20 |
19b |
a. Antennae filiform or serrate, much longer than head |
21 |
|
20a(19a) |
a. Antennae with 10 or fewer segments |
Lutrochidae, Lutrochus laticopes Casey |
b. Hind coxae contiguous |
20b |
a. Antennae with 11 segments |
Dryopidae (in part) |
b. Hind coxae separated |
|
21a(19b) |
a. Anterior coxae transverse with trochantin visible |
Dryopidae (in part) |
b. Antennae (if visible) very short, thick, with enlarged basal segment |
21b |
a. Anterior coxae round, trochantin concealed |
Elmidae (in part) |
b. Antennae slender, filiform |
|
22a(18b) |
a. Tarsi with 4th segment deeply bilobed |
Scritidae |
22b |
a. Tarsi usually filiform, 4th segment not bilobed |
23 |
|
23a(22b) |
a. Antennae filiform or clavate, partly concealed within prosternum |
Elmidae (in part) |
23b |
a. Antennae never concealed |
Psephenidae |
|