1.         Legs absent or not obvious from above . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

            Legs sometimes small, but always with 3-6 clearly defined segments . . . . . . . . . . . . . . . . . . 2

2.         Legs (excluding claws) wih 5 segments, tarsi with 2 claws (exception: Haliplidae with single             claw) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

           Legs with 3-4 segments; tarsi with a single claw. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3.         Abdomen with 2 pairs of stout, terminal hooks on segment 10; abdominal segments 1-9             bearing lateral gills. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gyrinidae

            Abdomen without hooks on terminal segment; abdominal segments usually without lateral gills,             occasionally with ventral gills. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

4.         Abdomen with 8 segments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

            Abdomen with 9 or 10 segments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

5.         Tarsus with single claw; mandible grooved internally; at least last larval instar with erect, dorsal             projectons from thoracic and abdominal tergites. . . . . . . . . . . . . . . . . . . . . . . . . .Haliplidae

            Tarsi with 2 claws; mandibles not grooved; tergites without projections. . . . . . . . Carabidae*

6.          Urogomphi slender, longer (usually much longer) than 1st abdominal segment. . . . . . . . . . . . .             . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dytiscidae (in part)

            Urogomphi stout, shorter than 1st abdominal segment or rudimentary or absent. . . . . . . . . . 7

7.          Legs short, stout, adapted for digging; mandibles with enlarged molar portion. . . . . . . . . . .             . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Noteridae, Hydrocanthus sp.

            Legs long, slender, adapted for swimming; mandibles falcate (sickle-shaped), without enlarged             molar portion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dytiscidae (in part)

8.          Labrum separated from clypeus by distinct suture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

            Labrum not represented as separate sclerite (the ventral labium may be visible dorsally). . . . . 9

9.          Body round or subcylindrical in cross section; head projecting anteriorly from prothorax and             visible from above; movable urogomphi often visible. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

            Body dorsoventrally flattened, with large, transverse thoracic and abdominal tergites (Fig.1.1);             pronotum expanded anteriorly, usually concealing head from above. .. . . . . . . . Lampyridae**

10.        Maxilla with palpifer apppearing as a segment of palpus; spiracles biforous (having 2 openings).             . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

            Maxilla with palpifer appearing as part of stipes; spiracles annular (ring-shaped); various             marginal habitats including intertidal. . . . . . . . . . . . . . . . . . . Staphylinidae, Philonthus sp.

11.        Abdomen with 8 segments, or rarely if with 10 segments, then urogomphi long, 2-3                         segmented, and legs long. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Hydrophilidae

12.        Thorax and abdomen short, obese, without distinct sclerites; legs reduced or absent. . . . . . 13

            Thorax and abdomen cylindrical, flattend, or fusiform (spindle-shaped), but not markedly             obese; thoracic and abdominal tergies clearly defined; legs adapted for walking. . . . . . . . . . 14

13.        Legs very small but complete and visible; spiracles on 8th abdominal segment forming large,             sclerotized dorsal hooks. . . . . . . . . . . . . . . . . . . Chrysomelidae, Donaclinae (rare in Ohio)

            Legs entirely absent; spiracles sometimes set on tubercles, but 8th segment never with                         sclerotized dorsal hooks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Curculionidae**

14.        Abdomen with 10 segments; 9th segment bearing articulated, 1- or 2 jointed. . . . . . . . . . 15

            Abdomen with 9 segments; 8th or 9th segment sometimes bearing immovable urogomphi, but             articulated urogomphi never present. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

15.        Mandibles with large, asperate (toughened) molar lobe. . . . . . . . . . . . . . . . . . . . . . . . . . . 16

            Mandibles falcate (sickle-shaped) without molar lobe; various marginal habitats included             intertidal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Staphylinidae, Philontus sp.

16.        Antennae much linger than head, multiarticulate (many jointed). . . . . . Scirtidae, Cyphon sp.

            Antennae short. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

17.        Body cylindrical, subcylindrical, or fusiform; head and legs visible in dorsal aspect. . . . . . . . 18

            Body extremely flattened, with thoracic and abdominal tergites expanded laterally as thin             laminae concealing head and legs from above (Fig. 1.2). . . . . . . . . . . . . . . . . . . Psphenidae

18.        Ninth abdominal segment with a lidike operculum covering the anal region ventrally; abdominal             sternites 1-8 never bearing gills. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

            Ninth abdominal segemtn without operculum; abdominal sternites 1-8 sometimes bearing             faciculate (clustered) gills. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

19.        Terminal abdominal segment rounded posteriorly; head capsule with groups of 6 stemmata             (ocelli), 5 lateral and 1 ventral, or stemmata (eyes) absent. . . . . . . . . . . . . . . . . . . . . . . . . 20

            Terminal abdominal segment bifid or slightly emarinate (notched) posteriorly and with lateral             ridges; head capsule with groups of 5 lateral stemmata. . . . . . . . . . . . . . . . . . . . . . . Elmidae

20.        Opercular chamber containing 2 retractile hooks and 3 tufts of retractile gills; mandibles with             prostheca. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lutrochidae, Lutrochus laticeps

           Opercular chamber without hooks or gills; mandibles without prostheca. . . . . . . . . . . . . . . . . . .             . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dryopidae, Helichus sp.

21.       Abdomen with distinct tufts of gills, either restricted to anal region or present on segments 1-7.            . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ptilodactylidae, Anchtarsus bicolor

*not listed for Ohio.

**not carried beyond family level.

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