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| The families of non-marine molluscs of Britain and Ireland (slugs, snails and mussels) |
Morphology. Snails, with a conspicuous, spiral, univalve shell.
The animal with one pair of tentacles only. Eyes at the bases of the tentacles.
The shell inoperculate; planispiral (nearly always), or rising-spiral (in Gyraulus crista only); 3–8 whorled; typically sinistral (when correctly interpreted, although carried by the animal upside down and hence appearing dextral when illustrated in its “natural” position. The morphologically upper side, as determined by the anatomy, is that which is uppermost when the shell is held with its aperture to the left of the observer); wider than high; 2–17 mm wide, or 25–35 mm wide (Planorbarius corneus); height about (0.15–)0.2–0.36(–0.44) x the width. The height of the spire about 0.12 x that of the shell (in the discoid Gyraulus crista, the rest being planispiral). The spire obtuse. The shell in Gyraulus crista, where the spire is raised, discoid. The whorls neither shouldered nor keeled, or shouldered, or keeled; conspicuously and regularly transversely ridged across the whorls (notably in Gyraulus crista, and in the Nautilus-like, internally segmented Segmentina nitida), or not conspicuously transversely ridged (then sometimes conspicuously ridged at irregular intervals). The aperture with neither teeth nor calluses. The shell with an umbilicus. The umbilicus large and wide. The shell thick-lipped to thin-lipped; thin and translucent to opaque; yellowish, brownish or olivaceous horn-coloured, occasionally whitish, sometimes more or less translucent, but often darkened by extraneous matter so as to appear blackish; plain. Morphological comments. Unlike that of most molluscs, the blood contains haemoglobin, so that a popular aquarium form of P. corneus with a translucent shell and lacking body pigment is bright red.
General biology, ecology. Freshwater aquatic. Breathing air directly via the lung-like mantle cavity (and via the skin in general). Water snails of diverse, well-vegetated aquatic habitats, with some species tolerant of seasonal dessication.
Hermaphrodite (but individuals acting as either male or female when mating).
Classification. Gastropoda; Pulmonata.
Representation in Britain and Ireland. “Ram’s-horn snails”: Anisus (3), Bathyomphalus (1), Gyraulus (4), Hippeutis (1), Menetus (1), Planorbarius (1), Planorbis (2), Segmentina (1).
Illustrations. • Anisus, Bathyomphalus, Gyraulus, Menetus, Planorbarius, Planorbis and Segmentina (with Physidae: Adams). PLANORBIDAE. 1, Segmentina nitida (Müller), "Shiny Ram's-horn". 2, Hippeutis complanatus (Linn.), "Flat Ram's-horn". 3, Gyraulus crista (Linn.), "Nautilus Ram's-horn". 4, Gyraulus albus (Müller), "White Ram's-horn". 5, cf. Gyraulus laevis (Alder), "Smooth Ram's-horn" (referred by Adams to Planorbis parvus Say.). 6, Anisus leucostoma (Millet), "Button Ram's-horn, White-lipped Ram's-horn". 7, Anisus vortex (Linn.), "Whirlpool Ram's-horn". 8, Planorbis carinatus Müller, "Keeled Ram's-horn". 9, Planorbis planorbis (Linn.), "Margined Ram's-horn". 10, Planorbarius corneus (Linn.), "Giant Ram's-horn". 11, Bathyomphalus contortus (Linn.), "Twisted Ram's-horn". 12, Menetus dilatatus (Gould), "Trumpet Ram's-horn". PHYSIDAE. 13, Aplexa hypnorum (Linn.), "Moss Bladder Snail"; 14, Physa fontinalis (Linn.), "Common Bladder Snail". From Adams (1896). • Anisus, Bathyomphalus, Gyraulus, Hippeutis, Planorbarius, Planorbis, Segmentina (Reeve). PLANORBIDAE. 1, Planorbarius corneus (L.), "Giant Ram's-horn". 2, Gyraulus albus (Müller), "White Ram's-horn". 3, Gyraulus laevis (Alder), "Smooth Ram's-horn". 4, Gyraulus crista (L.), "Nautilus Ram's-horn". 5, Planorbis carinatus Müller, "Keeled Ram's-horn". 6, Planorbis planorbis (L.), "Margined Ram's-horn". 7, Anisus vortex (L.), "Whirlpool Ram's-horn". 8, Anisus leucostoma (Millet), "Button Ram's-horn" or "White-lipped Ram's-horn". 9, Bathyomphalus contortus (L.), "Twisted Ram's-horn". 10, Hippeutis complanatus (L.), "Flat Ram's-horn". 11, Segmentina nitida (Müller), "Shiny Ram's-horn". From Reeve (1863, with scales added). • Anisus, Bathyomphalus, Gyraulus, Hippeutis, Menetus, Planorbarius, Planorbis, Segmentina (Ellis). PLANORBIDAE. 1–3, Planorbis planorbis (Linn.), "Margined Ram's-horn" (12–17 mm). 4–6, Planorbis carinatus Müller, "Keeled Ram's-horn" (12–15 mm). 7–10, Gyraulus acronicus (Férussac), "Thames Ram's-horn" (6–10 mm). 11 and 12, Gyraulus albus (Müller), "White Ram's-horn" (5–8 mm). 13–15, Gyraulus laevis (Alder), "Smooth Ram's-horn" (4.5–6 mm). 16 and 17, Gyraulus crista (Linn.), "Nautilus Ram's-horn" (2–3 mm). 18 and 19, Menetus dilatatus (Gould), "Trumpet Ram's-horn" (3–4 mm). 20 and 21, Anisus leucostoma (Millet), "Button Ram's-horn, White-lipped Ram's-horn" (5–8 mm). 22–24, iBathyomphalus contortus (Linn.), "Twisted Ram's-horn" (4.5–6 mm). 25–27, Anisus vortex (Linn.), "Whirlpool Ram's-horn" (7–10 mm). 28–31, Anisus vorticulus (Troschel) 3.5–6 mm. 32–34, Hippeutis complanatus (Linn.), "Flat Ram's-horn" (3–5 mm). 35–37, Segmentina nitida (Müller), "Shiny Ram's-horn" (4–5.5 mm). 38, Planorbarius corneus (Linn.), "Giant Ram's-horn" (25–35 mm). From Ellis (1926). • Planorbis corneus (J.A.). Planorbis corneus. Droylsden Canal, Manchester, J. Armitage. November 1950.
We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, and distributions of character states within any set of taxa. See also Guidelines for using data taken from Web publications.
Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2005 onwards. The families of non-marine molluscs of Britain and Ireland (slugs, snails and mussels). Version: 5th August 2019. delta-intkey.com’.
