Diagnostic characters
Shell like that of H. ulvae but with more slender spire which is more cyrtoconoid and has markedly tumid whorls and deep sutures. Aperture rounded adapically, its greatest breadth about the middle of its height. The snout is without an anterior dark transverse bar and the tentacles have no black transverse mark. Penis ends in a long flagellum.
Other characters
The shell has 5-7 whorls, its apical angle averaging 36°; it may be a dark or a pale brown. Up to 4.5 mm high, 2 mm broad; last whorl occupies 60-70% of shell height, aperture 35-40%.
The snout has dark lateral lines which converge posteriorly between the tentacles. There may be a dusky longitudinal line near the tip of each tentacle.
E. ventrosa prefers lower salinities (6-25%o) than H. ulvae (Nicol, 1936; Muus, 1963) and more sheltered localities, free from tidal movement (Cherrill & James, 1985); it tends to occur in drainage channels and lagoons with little direct contact with the sea and with soft bottoms and vegetation, preferring the latter. In East Anglian lagoons, it is known over a salinity range of l-36%o (Cherrill & James 1985; Barnes, 1987). Like H. ulvae it feeds on particles rasped from the substratum, but takes smaller ones, feeding best on those less than 40 µm in size, and not able to ingest those greater than 120 µm (Fenchel, 1975; Lopez & Kofoed, 1980). Its general geographical range is similar to that of ulvae but its occurrence is much more sporadic.
Eggs are laid April to July, each one in a capsule which is fastened to sand grains or the shells of other snails. It becomes obscured by adherent sand grains. A young snail emerges at hatching.