1. Worms large and robust, diameter 3 mm or more; posterior quadrangular in transverse section; with a thick clitellum. Lumbricidae, Eiseniella tetraedra
Worms can be long but are always thin, diameter 2 mm or less, and delicate; posterior segments round; with a poorly defined clitellum. . . . . . . . . . . . . . . 2
2. Dorsal and ventral setae in uniform groups of 2 or 4 and usually similar thoughout worm; setae short and stout, bifurcate or simple. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Lumbriculidae, Lumbrulus variegatus
Setae 2 or more per bundle, at least ventrally and anteriorly, but number, type and size varies, rarely similar dorsally (if present) and ventrally, setae simple, bifurcate, pectinate or palmate; hair setae present or absent. . . . . . . . . . . . . 3
3. Body papillate, roughened, or obsured with foreign matter. . . . . . . . . . . . . . 4
Body smooth or without adherent material. . . . . . . . . . . . . . . . . . . . . . . . . 7
4. With eyes. . . . . . . . . . . . . . . . Naididae, (in part), Slavina appendiculata
Without eyes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Body wall grandular and covered with foreign matter; ventral setae bifurcate, upper tooth much larger and longer than ventral. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Naididae, (in part), Stephensoniana trivandrana*
Body wall distinctly papillate, with some attached material; ventral setae simple or bifurcate, posteriorly the ventral tooth largest and very broad. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tubificidae, (in part), 6
6. Prostomium and segment I retractile (retracted in preserved specimens); mostly species with only a single set per bundle on posterior segments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Spirosperma ferox
Prostomium and segment I not clearly retractile; multiple ventral setae posteriorly. . . . . . . . . . . . . . . . . . . . . . . . . . . . Quistadrilus multisetosus
7. Specimens with anterior proboscis or several terminal appendages, gills or dorsal setae beginning after segment XV or dorsal setae absent. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Naididae (in part)
Specimens without any of these features. . . . . . . . . . . . . . . . . . . . . . . . . . . 8
8. With a proboscis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Without a proboscis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
9. Dorsal setae beginning on segment II. . Pristina aequiseta, Pristina leidyi
Dorsal setae beginning on segment IV or VI. . . . . . . . . . . . . . . . . . . . . . . 10
10. Dorsal hair setae in bundles of more than 3 (up to 18). Arcteonais lomondi*
Dorsal hair setae in bundles of 1-3. . . . . . . . . . . . . . . . . . Stylaria lacustris
11. With posterior gills enclosed in a hood (fossa). . . . . . . . . . . . . . . . . . . . Doro
Doro digitata, Dero furcata, Doro nivea
Without posterior gills. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
12. Without dorsal setae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chaetogaster
Chaetogaster diaphanus, Chaetogaster diastrophus, Chaetogaster limnaeili*
With dorsal setae absent before XVIII. . . . .. . . . . . . . Haemonis waldvogeli*
13. Dorsal setae beginning in segment II. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Dorsal setae beginnning in segment III or later. . . . . . Naididae (in part), 14
14. Dorsal setae beginning in segment III. . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Dorsal setae beginning in segment V or VI. . . . . . . . . . . . . . . . . . . . . . . . . 16
15. Dorsal setae beginning on segment V; no hair setae. . . . . . . . . Paranais frici
Dorsal setae beginniing on VI; with or without hair setae. . . . . . . . . . . . . . 17
16. Ventral setae of II-V different from those posterior to VI. . . . . . . . . . . . . Nais
Nais behningi, Nais communis, Nais elinguis, Nais pardalis, Nais simplex
Ventral setal similar throughout the body. . . .. . . . . . . . . . . . . . Piquetiella*
Piquetiella blanci*, Piquetiella michiganensis*
17. Dorsal setae bundle usually composed of 1-4 long hair setae and distinct, elongate, needlelike setae, simple or with nearly parallel teeth, with apex or teeth, with apex or teeth pointed upward; body length about 10 mm or less. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Dorsal setae typically curved apically with teeth oblique to shaft, hair setae present or absent; body usually well over 10 mm in length. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tubificidae (in part), 19
18. Doral setae commonly with 1 simple needle per bundle, occasionally a long , very thin hair seta. . . . . . . . . . . . . . . . . . . . . . . . . Bratislavia unidentata*
Dorsal setae bunles with 1-3 needle like setae, simple, bifurcate, or weakly pectinate, and 1-4 hair setae. . . . . . . . . . . . . . . . . . . . . . . . . . . Pristinella
19. Hair setae absent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Hair setae present. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
20. Dorsum of prostomium with a median pit and canal; modified ventral (genital) setae, if preseent with severly bent, beakllike tip. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bothrioneurum vejdovskyanum
Without a prostromial pit; modified ventral setae, if present, otherwise. . . . . 21
21. With simple setae anteriorly or posteriorly. . . . . . . . . . . Phallodrilus hallae*
No simple setae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
22. Mature worm with modified ventral setae from IX-XI, broad terminally, knoblike or spatulate. . . . . . . . . . . . . . . . . . . . . . . . . Rhizodrilus lacteus*
Mature worm with penial setae or penial setae otherwise. . . . . . . . . . . . . . . 23
23. Mature specimens with a pair of tubular short or long penial sheaths present in region of X and visible in cleared and weakly stained specimens. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Limnodrilus
Without tubular penial sheaths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
24. Mature worms with long, modified ventral setae on X, the distal portion fluted and hollow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Potomotrix*
Mature worm without modifiied ventral (genital) setae or modified setae otherwise. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
25. Setae bifurcate throughout. . . . . . . . . . . . . . . . . . . . . . . . . . Rhyacodrilus*
Setae diverse, especially posteriorly, either pectinate or wideened distally, or reduced to one with curved teeth. . . . . . . . . . . . . . . . . . . . . . . . . Autodrilus
26. Worm without modified ventral (genital) setae on X or XI. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ilyodrilus templetoni
With modified ventral (genital) setae on X or XI. . . . . . . . . Aulodrilus pigueti
*not reported for Ohio