> Dichotomous key
Georgia Atlantic Drainages

Disclaimers: (1) This key isn't literally dichotomous. (2) It is intended for use with the 37 species and subspecies of freshwater gastropods inhabiting Atlantic drainages of Georgia. 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 (19)

2a) Operculum concentric . . . . . . . (3)
2b) Operculum not concentric . . . . . . . (8)

3a) Adults under 6 mm maximum shell dimension . . . . Valvata    bicarinata   (Family Valvatidae).
3b) Adults greater than 6 mm maximum shell dimension . . . . (4)

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)

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

6a) Shell width approximately equal to, or sometimes greater than 
    shell height . . . Viviparus intertextus
6b) Shell narrower than high . . . . (7)

7a) Aperture greater than 50% of shell height . . . . Viviparus
    georgianus
7b) Aperture 50% of shell height or less . . . . . Campeloma decisum

8a) Adults over 6 mm shell length . . . . . Family Pleuroceridae (9)
8b) Adults under 6 mm shell length . . . . . Family Hydrobiidae (12)

9a) Shell entirely uncostate . . . . Goniobasis proxima
9b) Shell at least slightly costate . . . . (10)

10a) Shell strongly costate throughout . . . Goniobasis catenaria
    catenaria
10b) Shell with faint costae around apex only . . . . . (11)

11a) Shell slightly carinate . . . . Goniobasis catenaria dislocata
11b) Shell entirely without carination (vicinity of Hawkinsville) . . .
    Goniobasis floridensis timidus

12a) Penis simple, with a single duct . . . Somatogyrus virginicus 
12b) Penis with a single duct and a glandular terminal lobe . . . (13)
12c) Penis with a single duct and fringed with numerous papillae . . .     Littoridinops tenuipes
12d) Penis with two ducts . . . (17)

13a) Umbillicus imperforate, adults can be greater than 4.5 mm . . .
     Notogillia sathon
13b) Shell smaller, umbillicus at least slightly open . . . (14)

14a) Penis with a small terminal lobe, more than two additional
    glandular areas, and large penial filament . . . Spilochlamys turgida
14b) Penis with a small terminal lobe and not more than two                 additional glandular areas . . . (15)
14c) Penis with a large terminal lobe and a short filament . . . (16) 

15a) Ogeechee River . . . Marstonia halcyon
15b) Springs and spring-fed tributaries of the Ocmulgee River . . .         Marstonia agarhecta
15c) endemic to Rock Springs, a tributary of the Oconee River . . .         Marstonia gaddisorum

16a) Ogeechee River . . . . Floridobia species A.
16b) Southern coastal . . . Floridobia floridana

17a) Operculum entirely paucispiral . . . . Amnicola limosa
17b) Operculum initially multispiral, becoming paucispiral . . . (18)

18a) Shell substantially higher than wide . . . . Lyogyrus granum
18b) Shell roughly as wide as high, sometimes wider . . .
    Lyogyrus latus

19a) Shell dextral . . . . Family Lymnaeidae (20)
19b) Shell sinistral, not planispiral . . . . Family Physidae (22)
19c) Shell sinistral, planispiral . . . . Family Planorbidae (25)
19d) Shell patelliform . . . . Family Ancylidae (30)

20a) Aperture greater than 50% shell height . . . Lymnaea columella
20b) Aperture less than 50% shell height . . . (21)

21a) Lateral teeth of the radula tricuspid . . . . Lymnaea humilis
21b) Lateral teeth of the radula bicuspid . . . . Lymnaea cubensis

22a) One-part penial sheath . . . . . Physa acuta
22b) Two-part penial sheath . . . . (23)

23a) Shell slender, body generally dark . . . . Physa species A.
23b) Animal lightly pigmented, Shell with shoulders more
    pronounced . . . (24)

24a) Whorls convex . . . Physa gyrina
24b) Whorls not notably convex . . . Physa pomilia

25a) Adult greater than 5 mm shell diameter . . . . (26)
25b) Adult less than 5 mm shell diameter . . . . (28)

26a) Shell easily crushed with fingers . . . Biomphalaria obstructa
26b) Shell stronger . . . . (27) 

27a) Spire appears deeply indented when viewed from either aspect .
    . . Helisoma anceps
27b) Spire appears flattened when viewed from one aspect . . . .
    Helisoma trivolvis

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 distinctly to the right of midline . . . Hebetancylus
    excentricus
30b) Apex approximately in midline . . . . (31)

31a) Apex entirely smooth . . . . Laevapex fuscus
31b) Apex bearing fine striae . . . Ferrissia rivularis