Planorbella multivolvis

Planorbella multivolvis, the acorn ramshorn, was a species of small freshwater air-breathing snail, a pulmonate gastropod mollusk in the family Planorbidae, the ram's horn snails.

Planorbella multivolvis
Conservation status
Extinct  (IUCN 2.3)[1]
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Gastropoda
Superorder:	Hygrophila
Family:	Planorbidae
Genus:	Planorbella
Species:	†P. multivolvis
Binomial name
†Planorbella multivolvis (Case, 1847)

This species was endemic to the state of Michigan in the United States.^[2] It was last documented in 1907 and is now considered to be extinct.^[3][4]

The species was described to science in 1847 by William Case, who used the specific epithet "multivolvis" because the shells of this snail have a greater number of whorls than other members of the genus.^[5] The known range of the species was Howe Lake, in Marquette County, Michigan.^[2][3] It is thought that the species lived in the deeper waters of the lake, and came to shallow water only for the purposes of spawning.^[2] A possible cause of population decline is the introduction of sport fish to Howe Lake, which began in 1905, two years prior to the last known sighting of the species.^[3][6] A survey was conducted in 1989 and failed to locate any individuals.^[6]