Disclaimers: (1) This key isn't literally dichotomous. (2) It is intended for use with the 56 species and subspecies of freshwater gastropods inhabiting the Atlantic and Gulf drainages of Georgia, extending into the Florida panhandle, with one unconfirmed (U). The management will not be responsible for any loss, damage, or injury resulting from its application elsewhere.
1a) Operculum present. . . . . . Subclass Prosobranchia (2)
1b) Operculum absent . . . . . . Subclass Pulmonata (31)
2a) Operculum calcareous . . . Neritina usnea.
2b) Operculum corneous . . . (3)
3a) Operculum multispiral [photo] . . . (4)
3b) Operculum concentric [photo] . . . (5)
3c) Operculum paucispiral [photo] . . . (13)
4a) Adult shell bearing two carina . . . . Valvata bicarinata.
4b) Adult shell bearing three carina . . . Valvata tricarinata.
5a) Penis arising from the mantle edge, labial palps whiplike, eggs calcareous . . . Family Ampullariidae (6)
5b) Penis modified from a right tentacle, labial palps not whiplike, females ovoviviparous . . . Family Viviparidae (7)
6a) Shell whorls gently sloping, sutures not indented or incised . . . Pomacea paludosa.
6b) Sutures strongly incised . . . Pomacea maculata.
7a) Adults strikingly large; shells in excess of 40 mm standard length . . . Cipangopaludina japonica.
7b) Adults smaller . . . (8)
8a) Shell width approximately equal to, or sometimes greater than shell height . . . Viviparus intertextus.
8b) Shell narrower than high . . . . (9)
9a) Shell with color bands . . . . (10)
9b) Shell unbanded . . . . (12)
10a) Aperture length greater than half shell length . . . Viviparus goodrichi.
10b) Aperture length approximately half shell length . . . (11)
11a) Aperture length approximately equal to aperture width . . . Viviparus georgianus.
11b) Aperture length greater than aperture width . . . Viviparus limi.
12a) Shells striate, bearing spiral cords . . . Lioplax subcarinata.
12b) Shells smooth . . . Campeloma decisum.
13a) Adults over 10 mm shell length, both sexes present, oviparous . . . . . . . Family Pleuroceridae (14)
13b) Adults over 10 mm shell length, all female, ovoviviparous brooders . . . Melanoides tuberculata.
13c) Adults under 10 mm shell length . . . . . Hydrobioid families (19)
14a) Shell smooth with (at most) a single carination at apical whorls . . . (15)
14b) Shell sculptured . . . (16)
15a) Aperture length less than shell length . . . Pleurocera proxima.
15b) Aperture length greater than or equal to shell length . . . Pleurocera modesta.
16a) Ratio of body whorl length to total shell length greater than 0.62 . . . (17)
16b) Ratio less than 0.62 . . . (18)
17a) Shell sculpture light, becoming obsolete on body whorl . . . Pleurocera floridensis induta.
17b) Shell sculpture strongly plicate, no striations . . . Pleurocera curvicostata.
17c) Shell strongly plicate and striate . . . Pleurocera floridensis floridensis.
18a) Shell sculpture light, becoming obsolete on body whorl . . . Pleurocera catenaria dislocata.
18b) Shell strongly sculptured throughout . . . Pleurocera catenaria catenaria.
19a) Penis simple, with a single duct . . . Lithoglyphidae (20)
19b) Penis with a single duct and a bladelike terminal lobe . . . Hydrobiidae (21)
19c) Penis with a single duct and fringed with numerous papillae . . . Cochliopidae (27)
19d) Penis with two ducts . . . Amnicolidae (29)
20a) Adult shell never greater than 6 mm maximum dimension . . . Somatogyrus virginicus.
20b) Adult shell typically greater than 6 mm maximum dimension . . . Gillia altilis.
21a) Penis with a terminal lobe smaller than penial filament, bearing more than two glandular areas . . . Spilochlamys turgida.
21b) Penis with a terminal lobe smaller than penial filament, two glandular areas or fewer . . . Marstonia (22)
21c) Penis with a terminal lobe and penial filament approximately equal in size . . . (23)
21d) Penis with a terminal lobe much larger than penial filament . . . (25)
22a) Ogeechee River . . . Marstonia halcyon.
22b) Springs and spring-fed tributaries of the Ocmulgee River . . . Marstonia agarhecta.
22c) Endemic to Rock Springs, a tributary of the Oconee River . . . Marstonia gaddisorum.
23a) Shell aperture extending anteriorly beyond the whorl line . . . Spilochlamys conica.
23b) Shell aperture not extending beyond the whorl line . . . (24)
24a) Adult shell size greater than 6 mm standard length . . . Notogillia wetherbyi.
24b) Adult shell size less than 6 mm standard length . . . Notogillia sathon.
25a) Suture line deeply incised, shell whorls shouldered . . . Cincinnatia integra.
25b) Shell whorls smoothly rounded . . . (26)
26a) Ogeechee River . . . . Floridobia Species A.
26b) Southern coastal . . . Floridobia floridana.
27a) Penis with no more than six papillae . . . Aphaostracon monas.
27b) Penis with more than six papillae . . . (28)
28a) Width of a 4.0 mm adult shell less than 2.0 mm . . . Littoridinops tenuipes.
28b) Width of a 4.0 mm adult shell greater than 2.0 mm . . . Littoridinops monroensis (U).
29a) Operculum entirely paucispiral . . . . Amnicola limosa.
29b) Operculum initially multispiral, becoming paucispiral . . . (30)
30a) Shell substantially higher than wide . . . . Lyogyrus granum.
30b) Shell roughly as wide as high, sometimes wider . . . Lyogyrus latus.
31a) Shell dextral . . . . Family Lymnaeidae (32)
31b) Shell sinistral, not planispiral . . . . Family Physidae (34)
31c) Shell sinistral, planispiral . . . . Family Planorbidae (37)
31d) Shell patelliform . . . . Family Ancylidae (44)
32a) Aperture greater than 50% shell height . . . Lymnaea columella.
32b) Aperture less than 50% shell height . . . (33)
33a) First lateral tooth of the radula tricuspid . . . . Lymnaea humilis.
33b) First lateral tooth of the radula bicuspid . . . . Lymnaea cubensis/viator. [photos]
34a) One-part penial sheath . . . . . Physa acuta.
34b) Two-part penial sheath . . . . (35)
35a) Shell slender, body generally dark . . . . Physa carolinae.
35b) Animal lightly pigmented, Shell with shoulders more pronounced . . . (36)
36a) Whorls convex . . . Physa gyrina.
36b) Whorls not notably convex . . . Physa pomilia.
37a) Adult greater than 6 mm shell diameter . . . . (38)
37b) Adult less than 6 mm shell diameter . . . . (42)
38a) Shell easily crushed with fingers . . . Biomphalaria havanensis.
38b) Shell stronger . . . . (39)
39a) Spire appears deeply indented when viewed from either aspect . . . Helisoma anceps.
39b) Spire appears flattened when viewed from one aspect . . . (40)
40a) Juvenile shell bearing threadlike striae and acute keel . . . Helisoma trivolvis.
40b) Juvenile shell glossy, no keel [figure] . . . (41)
41a) Shell higher than wide in aperture view . . . Helisoma scalare scalare.
41b) Shell wider than high in aperture view . . . Helisoma scalare duryi.
42a) Shell with rounded periphery . . . Gyraulus parvus.
42b) Shell carinate . . . (43)
43a) Carina strong, approximately mid-whorl . . . Promenetus exacuous.
43b) Carina weak, distinctly off mid-whorl . . . Menetus dilatatus.
44a) Apex bearing fine radial striae . . . (45)
44b) Apex entirely smooth . . . . (46)
45a) Apex distinctly to the right of midline . . . Ferrissia fragilis.
45b) Apex approximately in the midline . . . Ferrissia rivularis. [photos]
46a) Apex approximately in the midline . . . . Laevapex fuscus.
46b) Apex distinctly to the right of midline . . . Hebetancylus excentricus.