Aplexa hypnorum, or by the common name, the moss bladder snail, is a species of small air-breathing freshwater snail, an aquatic pulmonate gastropod mollusk in the family Physidae, a family which are sometimes known as the bladder snails.

As is true of all physids, the shell is sinistral, or left-handed. The species inhabits temporary water bodies and occurs in the Eurosiberian Boreo-temperate or possibly the Eurasian Boreo-temperate if East Siberia specimens are correctly identified. It may be Holarctic, again if North American specimens are correctly identified.

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