Description: This small gastropod reaches up to 9 x 3 mm with a thin shell culminating in a pointed apex which may have a slight violet tinge. There are 8-9 flat-sided or slightly inflated whorls which have small ridges on their surface. It is light green to buff-coloured and may have longitudinal markings and darker marking between the ribs. The aperture is thin and almost triangular in shape.

Habitat: Associated with Zostera and similarly shaped algae, from low water mark onwards. Can tolerate reduced salinities/brackish water.

Distribution: Scattered records from all coasts of Britain and Ireland.

Similar Species: There are several other Rissoa species including Rissoa parva that could be confused with this species.

Key Identification Features:

• Shell culminates in a pointed apex often tinged with violet.
• 8-9 flattened or slightly inflated whorls.
• Light green to buff coloured with some longitudinal markings.
• Some dark markings between ribs.

Distribution Map from NBN: Rissoa membranacea at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Rissoa membranacea at iNaturalist World Species Observations database.

WoRMS: Rissoa membranacea at World Register of Marine Species.