Aquatic Macroinvertebrates of Ohio
1. Appearance sponge-like or blob of jelly (Fig. 1.1). . . . . . . . . . . . . . Sponges (Porifora)
Appearance not sponge-like. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Body without segments (Fig. 1.2). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Body segmented. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Body flattened (Fig. 1.3). . . . . . . . . . . . . . . . . . . Turbularia (flatworms, planarians)
Body elongate and cylindrical. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Large and elongate (greater than 1 cm in length) (Fig. 1.4). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nematomorpha (hairworms, horsehair worms)
Small (less than 1 cm in length). . . . . . . . . . . . . . . . . . . . . Nematoda (roundworms)
5. Shell present. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mollusca (clams & snails) 6
Shell absent - Note: be careful with this character because a hardened exoskeleton is often present. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6. Shell consists of one piece. . . . . . . . . . . . . . . . . . . . . . Gastropoda (snails & limpets)
Shell consists of two pieces (valves). . . . . . . . Bivalvia (freshwater mussels & clams)
7. Body with 20 or more segments; body shape worm-like (Fig. 1.5 or Fig. 1.6). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (Phylum Annelida - worms and leeches) 8
Body with fewer than 20 segments; body shape variable. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (Phylum Arthropoda - insects, spiders & crustaceans) 9
8. Suction disk present at one or both ends (Fig. 1.7). . . . . . . . . . . . Hirudinea (leeches)
Suction disk absent (Fig. 1.8). . . . . . . . . . . . . Oligochaeta (aquatic earthworms)
9. Four or more pairs of segmented legs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Three or no pairs of segmented legs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
10. Four pairs of segmented legs; antennae absent (Fig. 1.9). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (Class Arachnida - spiders & mites) 11
Five or more pairs of segmented legs; antennae present. . . . . . . . . . . . . . . . . . . . . . . . . . . . (Subphylum Crustacea - shrimps, crayfishes, sow bugs, water fleas, etc.) 12
11. Body consists of 2 segments (cephalothorax and abdomen). . . . . . . Araneae (spiders)
Body apparently unsegmented (Fig. 1.10). . . . . . . . . . Hydracarina (water mites)
12. Five pairs of segmented legs. . . . . . . . . . . (Order Decapoda - shrimps & crayfishes)
Seven pairs of segmented legs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
13. Hinged claws on the first three legs (first pair usually greatly enlarged) (Fig. 1.11). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cambaridae (crayfishes)
Hinged claws on first two legs (first pair not enlarged) (Fig. 1.12). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Palaemonidae (shrimp)
14. One antennal pair much longer than the other; body dorso-ventrally flattened (Fig. 1.13). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Isopoda - Asellidae (aquatic sow bugs)
Antennae of equal length; body laterally flattened (Fig. 1.14). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (order Amphipoda - scuds, sideswimmers)
15. Abdomen with 6 or fewers segments; wingless; small (usually less than 3 mm)(Fig 1.14). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (Collembola (springtails)
Abdomen with more than 6 segments; wings present or absent; size variable. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Insecta (insects) Go to Key to Aquatic Insects
