FWGNA > Freshwater Gastropods of Georgia > Dichotomous Key
Dichotomous Key
Georgia Atlantic Drainages

Disclaimers: (1) This key isn't literally dichotomous. (2) It is intended for use with the 40 species and subspecies of freshwater gastropods inhabiting Atlantic drainages of Georgia, plus 2 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 (21)

2a) Operculum multispiral [photo] . . . (3)
2b) Operculum concentric [photo] . . . (4)
2c) Operculum paucispiral [photo] . . . (9)

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)

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

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

7a) Shell with color bands . . . . Viviparus georgianus.
7b) Shell unbanded . . . . (8)

8a) Umbilicus slightly perforate . . . Bellamya japonica.
8b) Umbilicus imperforate . . . Campeloma decisum.

9a) Adults over 10 mm shell length, both sexes present, oviparous . . . . . . . Family Pleuroceridae (10) 
9b) Adults over 10 mm shell length, all female, ovoviviparous brooders . . . Melanoides tuberculata (U).
9b) Adults under 10 mm shell length . . . . . Family Hydrobiidae (13)

10a) Shell entirely uncostate . . . . Pleurocera proxima.
10b) Shell at least slightly costate . . . . (11)

11a) Shell strongly costate throughout . . . Pleurocera catenaria catenaria.
11b) Shell with faint costae, usually around apex only . . . . . (12)

12a) Shell slightly carinate . . . . Pleurocera catenaria dislocata.
12b) Shell entirely without carination (vicinity of Hawkinsville) . . . Pleurocera floridensis timidus.

13a) Penis simple, with a single duct . . . (14)
13b) Penis with a single duct and a glandular terminal lobe . . . (15)
13c) Penis with a single duct and fringed with numerous papillae . . . Littoridinops tenuipes.
13d) Penis with two ducts . . . (19)

14a) Adult shell never greater than 6 mm maximum dimension . . . Somatogyrus virginicus.
14b) Adult shell typically greater than 6 mm maximum dimension . . . Gillia altilis.

15a) Umbillicus imperforate, adults can be greater than 4.5 mm . . . Notogillia sathon.
15b) Shell smaller, umbillicus at least slightly open . . . (16)

16a) Penis with a small terminal lobe, more than two additional glandular areas, and large penial filament . . . Spilochlamys turgida.
16b) Penis with a small terminal lobe and not more than two additional glandular areas . . . (17)
16c) Penis with a large terminal lobe and a short filament . . . (18)

17a) Ogeechee River . . . Marstonia halcyon.
17b) Springs and spring-fed tributaries of the Ocmulgee River . . . Marstonia agarhecta.
17c) Endemic to Rock Springs, a tributary of the Oconee River . . . Marstonia gaddisorum.

18a) Ogeechee River . . . . Floridobia Species A.
18b) Southern coastal . . . Floridobia floridana.

19a) Operculum entirely paucispiral . . . . Amnicola limosa.
19b) Operculum initially multispiral, becoming paucispiral . . . (20)

20a) Shell substantially higher than wide . . . . Lyogyrus granum.
20b) Shell roughly as wide as high, sometimes wider . . . Lyogyrus latus.

21a) Shell dextral . . . . Family Lymnaeidae (22)
21b) Shell sinistral, not planispiral . . . . Family Physidae (24)
21c) Shell sinistral, planispiral . . . . Family Planorbidae (27)
21d) Shell patelliform . . . . Family Ancylidae (32)

22a) Aperture greater than 50% shell height . . . Lymnaea columella.
22b) Aperture less than 50% shell height . . . (23)

23a) Lateral teeth of the radula tricuspid . . . . Lymnaea humilis.
23b) Lateral teeth of the radula bicuspid . . . . Lymnaea cubensis.   [photos]

24a) One-part penial sheath . . . . . Physa acuta.
24b) Two-part penial sheath . . . . (25)

25a) Shell slender, body generally dark . . . . Physa carolinae.
25b) Animal lightly pigmented, Shell with shoulders more pronounced . . . (26)

26a) Whorls convex . . . Physa gyrina.
26b) Whorls not notably convex . . . Physa pomilia.

27a) Adult greater than 6 mm shell diameter . . . . (28)
27b) Adult less than 6 mm shell diameter . . . . (30)

28a) Shell easily crushed with fingers . . . Biomphalaria havanensis.
28b) Shell stronger . . . . (29)

29a) Spire appears deeply indented when viewed from either aspect . . . Helisoma anceps.
29b) Spire appears flattened when viewed from one aspect . . . Helisoma trivolvis.

30a) Shell with rounded periphery . . . Gyraulus parvus.
30b) Shell carinate . . . (31)

31a) Carina strong, approximately mid-whorl . . . Promenetus exacuous.
31b) Carina weak, distinctly off mid-whorl . . . Menetus dilatatus.

32a) Apex bearing fine radial striae . . . Ferrissia fragilis.
32b) Apex entirely smooth . . . . (32)

33a) Apex approximately in the midline . . . . Laevapex fuscus.
33b) Apex distinctly to the right of midline . . . Hebetancylus excentricus.