Ammonitella yatesii

Tight Coin (=yates' Snail)

Family: Megomphicidae · Class: Gastropoda · Order: Stylommatophora

Conservation status: G1 S1

Ammonitella yatesii, commonly known as the tight coin or Yates' snail, is a terrestrial gastropod mollusk in the family Megomphicidae. This small land snail is characterized by its tightly coiled, coin-shaped shell, from which its common name derives. The shell typically exhibits a planispiral coiling pattern with multiple whorls compressed into a relatively flat, disc-like structure. Adult specimens measure approximately 3 to 5 millimeters in diameter, making this one of the smaller terrestrial snail species in North America. The tight coin is endemic to a restricted range in the southeastern United States, with historical records primarily from Alabama and Tennessee within the Mobile River Basin. The species' extremely limited distribution contributes to its conservation concern, as populations are confined to specific limestone substrates and associated habitats. Current population status and precise locality information remain poorly documented due to the species' rarity and cryptic nature. This species inhabits limestone outcrops, cave entrances, and associated rocky substrates in forested environments. The tight coin requires specific microhabitat conditions, including consistent moisture levels and appropriate calcium carbonate availability for shell development. These snails are typically found in areas with abundant leaf litter and organic debris, which provide both shelter and food sources. The species appears to be closely associated with limestone geology, which provides the calcium necessary for shell formation and maintenance. As a terrestrial gastropod, the tight coin is likely detritivorous, feeding on decomposing organic matter, fungal hyphae, and microorganisms found in leaf litter and soil. Like most land snails, reproduction involves hermaphroditic individuals that can both give and receive sperm during mating. Egg-laying likely occurs in moist soil or under protective cover such as rocks or logs. Seasonal activity patterns are not well documented, though most terrestrial snails in temperate regions are most active during periods of high humidity and moderate temperatures. The tight coin is classified as G1 S1 (critically imperiled globally and statewide), indicating extreme rarity and high risk of extinction. This ranking reflects the species' highly restricted range, small population size, and vulnerability to habitat disturbance. The U.S. Fish and Wildlife Service maintains taxonomic records for this species, recognizing its conservation significance within the broader context of southeastern aquatic and terrestrial ecosystem management. Primary threats likely include habitat modification, limestone quarrying, and general disturbance of forest floor communities. The species' dependence on specific geological and microhabitat conditions makes it particularly vulnerable to environmental changes. Detailed ecological studies and population monitoring are needed to better understand this species' biology, distribution, and conservation requirements. The tight coin represents part of the endemic mollusk fauna of the southeastern United States, which includes numerous rare and narrowly distributed species requiring targeted conservation attention.

Data from The California Species Project — 14,000+ California species with verified data from CNPS, CDFW, USFWS, and more.