A List of California Endemic Terrestrial Gastropods

 

The terrestrial gastropod fauna of California contains some of the highest endemism of any group, and, surprisingly, some of its most emblematic species (i.e. the banana slugs). Similar to its millipede and salamander diversity, the snail and slug diversity of California's rugged landscape is outdone only by The Appalachians, at least in North America. The state of Tennessee holds the greatest number of land gastropods (263), with California coming in second (248), followed by North Carolina (214), and Virginia (208). The humid southeast contains a fair snail diversity, as well, with Alabama (192), Texas (182), and Louisiana (125) leading (Perez et. al. 2008). 

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California's gastropod richness is anomalous in the west, as the surrounding states are comparatively low in diversity, presumably a result of fewer opportunities for allopatric speciation, a likely driver for speciation among these mobility-impaired organisms. So, in spite of its moist conditions, the remainder of the Pacific Northwest is not particularly rich in Gastropods. Oregon and British Colombia contain only 78 species each, and Washington has 86. 

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On a global scale, terrestrial gastropods are most abundant in tropical rainforests, where they can attain surprisingly showy and colorful forms in Hawaii, Sri Lanka, India, Cuba, Thailand, and many other regions. Comparatively showy snails occur in the United States, as well, with such distinctive species as the Florida tree snail and the celebrated banana slugs of western North America. 

 

Terrestrial gastropods are more susceptible to endangerment than any other animal group. More land snails have gone extinct than in all other animal orders combined. 

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California Land Gastropod Endemism

 

California is rich with snail microendemism. A total of 75% of the native snails and slugs in the California Biological Region are endemic to it, many confined to single mountain ranges, mountains, islands, or elevational bands. The isolation of California's biodiversity stands out here, with a total of 16 genera being endemic to the region, and 7 near-endemic:

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Endemic Gastropod Genera:

Anandenulus

Binneya

Chamaearionta

Eremariontoides

Helminthoglypta

Herpeteros

Micrarionta

Mohavelix

Noyo

Rothelix

Sonorelix

Xerarionta

Amonitella

Glyptostoma

Polygyroidea

Triolobopsis

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Near-Endemic and Semi-Endemic Gastropod Genera:

Ariolimax (88%)

Hesperarion (75%)

Monadenia (92%)

Haplotrema (60%)

Cauhillus (71%)

Eremarionta (71%)

Vespericola (86%)

Nearctula (50%)

Pristiloma (40%)

 

The genus Helminthoglypta, known as the shoulderband snails, contributes the highest diversity to California snail fauna, with a total of 73 species, all found exclusively within the region - mostly within the California Floristic Province. The next most abundant genus is Monadenia, the (by North America standards) colorful side-bands, for which all 14 species occur in California and 13 of these are endemic. 

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A closer look into California's native gastropods reveal such curiosities as the Badwater snail, found in the infamously sterile waters of Death Valley's Badwater salt flats; the American keeled slug, only member of the genus Anandenulus, which was thought extinct until 2018; and several genera of rare desert-dwelling snails representing relictual vestiges. 

 

Most famous among California's gastropods are the banana slugs (Ariolimax spp.), whose brilliant yellow forms are known worldwide as a confusing University mascot, a tourist attraction of the Pacific Northwest, and as one of the world's largest land slug species. The banana slug is, in fact, the second-largest land slug species in the world, following the ash-backed slug (Limax cinereoniger) of Europe. Seven (7) of eight banana slug species are endemic to California, although the majority of these remain unnamed or unassigned at the time of the death of Dr. John Pearse, the authority on Ariolimax, in 2020. 

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For this project, I intend to photograph all 248 endemic species, with at least one member from each genus being photographed in the wild. 

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A complete list of endemic Californian terrestrial gastropods can be found here.

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