A Tale Of Two Cities
By Harry G. Lee
     A pair of urban centers in the American South, Jacksonville, Florida and Mobile, Alabama, may seem odd choices for a Dickensian title, but, to indulge the Southern idiom, "thereby hangs a tale," at least so it seems malacologically.

     The two port cities have several common features such as altitude, latitude, rainfall, and temperature and are separated only by the breadth of North Florida. Interestingly, their native land snails are better known than those of any metropolis today. Eminent students like L. H. MacNeill, H. H. Smith, Bryant Walker, A. D. Brown, and Leslie Hubricht have provided data and taxonomic insights which have given stimulus and guidance to two Jacksonville Shell Club members, Mobilian Wayne Sullivan and the writer, in developing an understanding of the two land snail faunas. The report which follows is an attempt to summarize these data and understand the similarities and differences between the two.

     Table 1. lists all 80 species of terrestrial snail native to at least one of the cities (Here "Jacksonville" includes records for Clay, Duval, and St. Johns Counties; "Mobile" includes Mobile and Baldwin Counties). The columns separate those snails found in one, the other, or both places. While producing an obligingly perfect numerical symmetry (1 Jacksonville/3 both cities/1 Mobile) in this analysis, the data depicted in tables 2 and 3 show a remarkable contrast in the general distribution of those species limited to only one of the cities.

Table 1 - Land Snails

Mobile Only

Both Cities

Jacksonville Only

1.   Daedalochila auriculata
2. Daedalochila auriformis    
3.   Daedalochila avara
4. Polygyra cereolus  
5.   Daedalochila hausmani
6. Lobosculum leporinum    
7.   Daedalochila peninsulae
8. Millerelix plicata    
9. Lobosculum pustula  
10. Lobosculum pustuloides  
11. Daedalochila subclausa  
12. Polygyra septemvolva  
13.   Praticolella bakeri(2)
14.   Praticolella jejuna
15. Praticolella lawae    
16. Praticolella mobiliana  
17. Tridopsis hopetonensis  
18.  

Tridopsis messana

19.

Inflectarius inflectus

 
20. Patera perigrapta    
21.

Mesodon thyroidus

 

22. Euchemotrema leai
 

   
23.   Drymaeus dormani
24. Euglandina rosea  
25. Haplotrema concavum    
26. Euconulus chersinus  
27. Euconulus trochulus(1)  
28. Dryachloa dauca  
29.   Guppya gundlachi
30. Guppya sterkii(2)  
31. Glyphyalinia umbilicata  
32. Glyphyalinia luticola(2)  
33. Glyphyalinia solida  
34.   Nesovitrea dalliana
35. Striatura meridionalis  
36.   Hawaiia alachuana
38. Mesomphix globosus  
39. Paravitrea conecuhensis    
40.   Ventridens cerinoideus
41. Ventridens demissus    
42. Ventridens intertextus    
43.   Ventridens volusiae
44. Zonitoides arboreus  
45. Anguispira strongylodes    
46. Helidociscus notius notius(1)  
47. Helicodiscus parallelus  
48. Discus patulus    
49. Punctum minutissimum  
50. Philomycus carolinianus  
51. Catinella oklahomarum(1)  
52. Catinella vermeta  
53.   Oxyloma effusum
54. Succinea campestris  
55. Succinea unicolor  
56. Strobilops aeneus  
57. Strobilops hubbardi  
58. Strobilops texasianus  
59. Gastrocopta armifera(1)    
60. Gastrocopta contracta  
61. Gastrocopta pellucida  
62. Gastrocopta pentodon  
63.  Gastrocopta riparia    
64. Gastrocopta rupicola  
65.   Gastrocopta servilis
66. Gastrocopta tappaniana  
67. Pupoides albilaris  
68. Pupoides modicus  
69. Pupisoma dioscoricola  
70. Pupisoma macneilli(3)  
71. Vertigo conecuhensis    
72. Vertigo milium  
73. Vertigo oralis  
74. Vertigo oscariana  
75. Vertigo ovata  
76. Vertigo rugosula  
77. Vertigo teskeyae  
78. Carychium mexicanum  
79.   Leidyula floridana (4)
80. Helicina (Olygyra) orbiculata  

16 species total

48 species total

16 species total

(1) Not documented, but strongly suspected to occur in Mobile.

(2) Not documented, but strongly suspected to occur in Jacksonville.

(3) I unite Pupisoma minus with P. macneilli on advice from L. Hubricht.

(4) Possibly introduced from a more southerly point in Florida.

Table 2 - General Distribution of "Mobile Only" Snails

Basic Gulf Costal Plain (Including a portion of the Mississippi River Valley)

Endemic

Widespread, Basic Piedmont

Daedalochila auriformis

 

 

Lobosculum leporinum

 

 

Millerelix plicata

 

Praticolella lawae

 

 

Inflectarius inflectus

 

 

Mesodon perigraptus

 

 

Stenotrema monodon al.

 

 

Haplotrema concavum

 

Paravitrea conecuhensis

 

 

 

Ventridens demissus

 

 

Ventridens intertextus

 

 

Anguispira stronglodes

 

 

Discus patulus

 

 

Gastrocopta armifera

Gastrocopta riparia

 

 

 

Vertigo conecuhensis

 

Table 3 - General Distribution Of "Jacksonville Only" Snails

Basic S. E. Costal Plain

Endemic

Florida / West Indies

 

Daedalochila auriculata

 
 

Daedalochila avara

 
 

Daedalochila hausmani

 
 

Daedalochila peninsulae

 
 

Praticolella bakeri

 
 

Praticolella jejuna

 

Triodopsis messana

   
 

Drymaeus dormani

 
   

Guppya gundlachi

Hawaiia alachuana

Nesovitrea dalliana

 

Ventridens cerionoideus

   
 

Ventridens volusiae

 

Oxyloma effusum

 

 
 

 

Gastrocopta servilis

   

Veronicella floridana

Go To Images Of The Seven Vertigo Species Listed Above

     Each city has four species of its own which are limited in general distribution to the adjacent coastal plain. Just what barriers exist between the Gulf and South Atlantic segments of the plain are not obvious, but clearly some land snail species have respect for them.

     Some of the "Jacksonville only" species clearly came here from tropical areas considerably to our south. Two of the three, Guppya gundlachi and Gastrocopta servilis, are quite widespread in the Caribbean area.

     Both cities are situated on the estuaries of large, but geologically different, rivers. Whereas the St. Johns never leaves the low coastal plain, the Mobile arises high in the Piedmont of Mississippi, Alabama, and Georgia. Those species comprising the majority of the "Mobile only" snails (10) are widespread on the Piedmont region and may well have reached Mobile via the Alabama or Tombigbee Rivers from remote upstream origins.

     Despite the special provenance of Mobile's alluvium, Jacksonville is able to even the species score in table 1 because of a greater degree of "endemnicity." Those species in the middle columns of tables 2 and 3 are rather limited in general distribution (for the sake of clarity, we might say limited to an area less than either state). Jacksonville "endemics" outnumber Mobile "endemics" by nine to two. The probable explanation of Jacksonville's lopsided advantage lies in the geologic history of the Florida peninsula.

     The Pleistocene epoch, beginning about 1,800,000 years ago and extending to about 25,000 BC, was characterized by rapid, severe changes in the Earth's surface temperatures. The changes were manifest, as most former highschoolers will recall, as the Ice Ages - with the advance and recession of great glaciers. The glacial ice was in the ultimate analysis derived from the seas, and sea levels fell and then rose as the glaciers advanced and then receded. As one might expect, shorelines were profoundly affected during the Ice Ages. One can first visualize the fall of sea level, exposing much of the Continental Shelf, during the glacial advances. What may come as a surprise is that at certain Pleistocene times the sea level was considerably higher than at present (less polar ice than today). In fact, during the warmest portion of the Pleistocene, the peninsula of Florida was inundated to the extent that there was only a nubbin of a peninsula and a few islands above water (black areas depicted on the map below).

Florida showing the shoreline at the time of the highest Pleistocene Sea. This is called the Wicomico shoreline. Adapted from C. W. Cooke (1945) Geology of Florida Florida Geological Survey Bulletin 29 339 pp.

     Now, most evolutionists agree that the geographic isolation of populations of living things is a principal force in speciation. A glance at the map will make it clear how the Pleistocene epoch provided Florida geographic barriers on a grand scale. (Southern Alabama underwent much less extensive change - roughly like that of the Florida panhandle). Dr. Fred Thompson* has shown how extensive speciation occurred in the freshwater Hydrobiid snails during the Florida Pleistocene. The evidence seems to indicate that land snails, especially members of the family Polygyridae (the first six Jacksonville "endemics"), underwent a similar orgy of speciation, probably on islands created during the warmest phases. In looking at the moderately restricted ranges of certain "both cities" species (e.g., nos. 9, 11, 16, 28, 55, 57, 68, 70), one must also suspect a similar Pleistocene Floridian origin.

     Just why those nine Jacksonville "endemics" have reached North Florida and gotten very little further (including S. E. Georgia in one case) is a difficult question to answer, but it appears likely that there are habitats in Mobile in which most or all these species could thrive. There are probably subtle ecological barriers which impede the the already slow northern and western spread of these snail populations. A "snail's pace" is certainly a good characterization of the vagility (ability to move in a biogeographical sense) of any of our land mollusks. The lack of motility and perhaps some of the infective Florida sunshine possibly conspired to maintain 1 of 7 Jacksonville native land snails in complacent, relatively permanent isolation.

*Thompson, Fred G. (1968) Aquatic snails of the family Hydrobiidae of Peninsular Florida University of Florida Press, Gainesville pp 268 plus xv, 69 fig. 3 tab.

Note: Taxonomy updated on 5/3/2007 and 3/1/2011.

 
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