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.

[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] 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.