|Researched by||Chloe Wilson||Refereed by||Admin|
|Other common names||-||Synonyms||Trochus magus (Linnaeus, 1758), Gibbula forskadauri (Nordsieck, 1982)|
A large top shell usually broader than it is tall (up to 3.5 cm high and 3.0 cm across). The shell is blunt and conical. The base of the shell bears a wide and deep central cavity (umbilicus) outlined by a thick ridge partly obstructed by the inner lip. The shell is stepped with up to eight whorls, each with a variable number of ridges and grooves. Round bumps (tubercles) are found on the upper surfaces of the whorls. The shell colour varies from white to grey to yellowish. The shell is decorated with irregular flecks of red, brown or purple. Intertidal specimens may be markedly smoother than those found in the subtidal.
The animal itself is yellow-pink or orange in colour with black or purple spots. The front of the foot is blunt whilst the back is pointed and has three pairs of sulphur yellow tentacles with white sheaths. A rounded plate (operculum) closes the shell opening when the body is withdrawn into the shell.
Found at all latitudes in Britain from north Scotland to the south west of England and along the English Channel. Records are concentrated on western coasts, with few records from the east coast and the North Sea. In Ireland, Gibbula magus is patchily distributed around all coasts.
Gibbula magus is found in parts of the North East Atlantic, extending north from the eastern Mediterranean (Egypt) and the Azores to its northern limits in the Shetland Islands, Scotland.
Restricted to the extreme low water of spring tides (ELWST) in the intertidal, where it is found on shingle or rocky substrata under stones and on weed. It is found at depths of up to 70 m in the subtidal on rock, muddy gravel, and muddy sand.
Food sources include microbes and detritus (Fish & Fish, 1996). They are dioecious and eggs are laid only in the spring and early summer after external fertilization (Graham, 1988; Fish & Fish, 1996).
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Fish, J.D. & Fish, S., 1996. A student's guide to the seashore. Cambridge: Cambridge University Press.
Graham, A., 1988. Molluscs: prosobranchs and pyramellid gastropods (2nd ed.). Leiden: E.J. Brill/Dr W. Backhuys. [Synopses of the British Fauna No. 2]
Hayward, P., Nelson-Smith, T. & Shields, C. 1996. Collins pocket guide. Sea shore of Britain and northern Europe. London: HarperCollins.
Hayward, P.J. & Ryland, J.S. (ed.) 1995a. The marine fauna of the British Isles and north-west Europe. Volume 2. Molluscs to Chordates. Oxford Science Publications. Oxford: Clarendon Press.
Hayward, P.J. & Ryland, J.S. (ed.) 1995b. Handbook of the marine fauna of North-West Europe. Oxford: Oxford University Press.
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Last Updated: 18/08/2017
Tags: topshell top-shell