Hydrobia ulvae
<p><em>Hydrobia ulvae</em> (Pennant, 1777)</p>
Hydrobia ulvae
North Norway to Senegal, including Baltic and Mediterranean. Very common on estuaries and saltings all round Britain and Ireland.
Hydrobia ulvae is very common on bare intertidal wet sand and mud, especially on estuaries and saltings at salinities 5- 40 p.p.t.. Also on Enteromorpha and Ulva and in pools with soft substrate. Often at densities 5000 –9 000 /sq.metre, and occasionally to 42 000 /sq.metre. At all shore levels, varying with local substrate conditions. Feeds on small organic particles, diatoms and bacteria while crawling on substrate or lying buried except for aperture. When submerged, may float at water surface with aid of a mucus raft which traps diatoms etc. in the neuston. Spawn; gelatinous masses, covered in sand, containing up to 25 eggs or more, attached to shells of other individuals in spring and summer. Short veliger larva stage.An important part of the ecosystem in estuaries and saltings, providing food for birds, fish and parasites, altering the substrate with its faeces and affecting the abundance of the micro-organisms it feeds on.
Potamopyrgus antipodarum (J.E. Gray, 1843)
- Adapical angle of shell aperture rounded.
- Translucent grey tentacles often with fine white medial line, no subterminal black mark and no white flecks apart from basal patch in front of eye.
- Usually in fresh or brackish (0-16 p.p.th.) water.
Hydrobia ventrosa (Montagu, 1803)
- Adapical end of shell aperture rounded.
- Tentacles lack black transverse band, but may have longitudinal dusky streak near tip.
- Lagoons, non-tidal, salinity 1-36 p.p.t., with soft substrate & vegetation.
Hydrobia acuta neglecta Muus,1963
- Adapical end of aperture pointed.
- White tentacles; tips covered with long thin black cone except for paler extreme apex and white intrusion into base of cone dorsally.
- Snout has subterminal black band, like many H. ulvae, but rest of head black except for two whitish oval areas on snout.
- Small, 4mm maximum height.
- Lagoons, non-tidal, salinity 10-35 p.p.t., with soft substrate & vegetation.
Assiminea grayana Fleming, 1828
- Adapical end of aperture pointed.
- Tentacles short grey to black stumps with eye on dorsal surface near tip.
- Grey snout with wide central cleft, head darker.
- Near high water mark on saltings and tidal rivers.
- Adapical angle of aperture pointed.
- Translucent tentacles with black subterminal band and, usually, many white/yellow pigment flecks.
- Left tentacle thicker and less smooth than right tentacle.
Fretter, V. and Graham, A. 1962. British prosobranch molluscs. London, Ray Society.
Graham, A. 1988. Prosobranch and pyramidellid gastropods. London.
Green, J. 1968. The biology of estuarine animals. London.
Yonge, C.M. and Thompson, T.E. 1976. Living marine molluscs. London.
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