Haminoea hydatis is a species of sea snail or bubble snail, a marine opisthobranch gastropod mollusc in the family Haminoeidae, one of the families of bubble snails.
An adult Haminoea hydatis can be as long as 8-, while the shell reaches a length of 8-. It is a fragile, inflated, oblong shell partially hidden by the mantle and parapodial lobes in crawling animals. These herbivorous swimming snails are dark brown.
This species is present in SW Britain, Ireland, France and south to the Mediterranean, Madeira and Canaries; Ascension Island, St. Helena and west coast of Africa. These snails live on muddy sands, shell grit and algae fields.