1. Hydrobia ulvae aperture and operculum. Arrow indicates pointed adapical end of aperture. From salting pool, salinity 22.7p.p.t., Aust, Severn Estuary. Most specimens from this site with sulphide-rich anaerobic mud had extensive black encrustation.
2. Hydrobia ulvae aperture and operculum. Arrow indicates pointed adapical end of aperture. From salting pool, salinity 22.7p.p.t., Aust, Severn Estuary. Most specimens from this site with sulphide-rich anaerobic mud had extensive black encrustation.

Hydrobia ulvae aperture and operculum. Arrow indicates pointed adapical end of aperture. From salting pool, salinity 22.7p.p.t., Aust, Severn Estuary. Most specimens from this site with sulphide-rich anaerobic mud had extensive black encrustation.