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