Disclaimers:� (1) This key isn�t literally dichotomous.� (2) It is intended for use with the 39 species and subspecies of freshwater gastropods inhabiting the state of South Carolina.� 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 (18)

2a)�Operculum multispiral [photo]�. . . (3)
2b)�Operculum concentric [photo] . . .�(4)
2c) Operculum paucispiral [photo] . . . (11)

3a) Adult shell�bearing two carina . . . Valvata bicarinata.
3b) Adult shell�bearing three carina . . . Valvata tricarinata.

4a) Penis arising from the mantle edge, labial palps whiplike, eggs calcareous . . .� Family Ampullariidae (5).
4b)� Penis modified from a right tentacle, labial palps not whiplike, females ovoviviparous . . . Family Viviparidae (6).
4c) Population entirely female, parthenogenic . . . (6).

5a) Shell whorls gently sloping, sutures not indented or incised . . . Pomacea paludosa.�
5b) Sutures strongly incised . . . Pomacea�maculata.

6a) Aperture rounded . . .�(7)
6b) Aperture oblong,�noticably longer than wide . . . (10)

7a) Adults strikingly large, shells in excess of 40 mm standard length . . . Cipangopaludina japonica.
7b) Adults smaller . . . Viviparus (8)

8a) Shell width approximately equal to, or sometimes greater than, shell height . . . Viviparus intertextus.
8b) Shell narrower than high . . . (9)

9a) Shell rounded, with color bands . . . Viviparus georgianus.
9b) Shell with flattened sides, unbanded . . . Viviparus subpurpureus.

10a) Shell bearing spiral cords . . . Lioplax subcarinata.
10b) Shell smooth . . . Campeloma decisum decisum.

11a) Adults over 10 mm shell length, all female, ovoviviparous brooders. . . Melanoides tuberculata.
11b) Adults over 10 mm shell length, both sexes present, oviparous . . . . . Family Pleuroceridae (12)
11c) Adults under 10 mm shell length . . . . .�Hydrobioid families (13)

12a) Shell uncostate . . . . Pleurocera proxima.
12b) Shell costate (sometimes faint, around apex only).� Spiral cords, if present, restricted to juvenile whorls only . . . Pleurocera catenaria dislocata.
12c) Shell costate, bearing spiral cords throughout . . . Pleurocera catenaria catenaria.

13a) Penis simple . . . (14)
13b) Penis bifurcated . . . (15)
13c) Penis fringed with numerous papillae . . . (17)

14a) Adults never greater than 6 mm . . . Somatogyrus virginicus.
14b) Adults generally greater than 6 mm . . . Gillia altilis.

15a) Operculum entirely paucispiral . . . . Amnicola limosa.
15b) Operculum initially multispiral, becoming paucispiral . . . (16)

16a) Shell length greater than shell width . . . Lyogyrus granum.
16b) Shell length equal to or greater than shell width . . . Lyogyrus latus.

17a) Shells polymorphic, including morphs with carinae and spines . . . Pyrgophorus parvulus.
17b) Shells never carinate or spiny . . . Littoridinops tenuipes.

18a) Shell dextral . . . . Family Lymnaeidae (19)
18b) Shell sinistral, not planispiral . . . . Family Physidae (21)
18c) Shell sinistral, planispiral . . . . Family Planorbidae (23)
18d) Shell patelliform . . . . Family Ancylidae (30)

19a) Aperture greater than 50% shell height . . . Lymnaea columella.
19b) Aperture less than 50% shell height . . .� (20)

20a)� First lateral tooth of radula bicuspid . . . Lymnaea cubensis/viator.
20b)� First lateral tooth of radula tricuspid . . . Lymnaea humilis. � [photos]

21a) One part penial sheath . . . . . Physa acuta.
21b) Penial sheath constricted into two parts . . . (22)

22a) Shell slender, body generally dark . . . . Physa carolinae.
22b) Animal lightly pigmented, Shell with shoulders more pronounced . . . Physa pomilia.

23a) Adult greater than 5 mm shell diameter . . . . (24)
23b) Adult less than 5 mm shell diameter . . . . (28)

24a) Shell easily crushed with finger pressure . . . Biomphalaria havanensis.
24b) Shell stronger . . . (25)

25a) Spire appears deeply indented when viewed from either aspect . . . Helisoma anceps.
25b) Spire appears flattened when viewed from one aspect . . . . (26)

26a) Juvenile shell bearing threadlike striae & acute keel . . . Helisoma trivolvis.
26b) Juvenile shell glossy, no keel [figure] . . . (27)

27a) Shell higher than wide in aperture view . . . Helisoma scalare scalare.
27b) Shell wider than high in aperture view . . . Helisoma scalare duryi.

28a) Shell with rounded periphery . . . . Gyraulus parvus.
28b) Shell carinate . . .� (29)�

29a) Carina strong, approximately mid-whorl . . . Promenetus exacuous.
29b) Carina weak, distinctly off mid-whorl . . . Menetus dilatatus.

30a) Apex bearing fine radial striae . . . (31).
30b) Apex entirely smooth . . . . (32)

31a) Apex distinctly to the right of midline . . . Ferrissia fragilis.
31b) Apex approximately in the midline . . . Ferrissia rivularis. �[photos]

32a) Apex approximately in the midline . . . . Laevapex fuscus.
32b) Apex distinctly to the right of midline . . . Hebetancylus excentricus.