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 Osilinus lineatus is the largest intertidal trochid in Britain. The shell is a turbinate spire consisting of up to six whorls. The last whorl dominates the shell and ends in a circular aperture, with a prominent 'tooth' or bulge on the nacreous (mother-of-pearl) inner shell layer. The outer lip of the aperture is thinner than the rest of the shell.

Shell colour varies between dark green, grey and black, with complex brown or purple zigzag markings. The shell can reach up to 3cm in height (Graham, 1988) and 3cm basal diameter and is thicker and heavier than other species of topshell found in Britain. Shell growth lines are visible (Desai, 1966; Fretter & Graham, 1977; Williamson & Kendall, 1981). Erosion of the outer layer of the shell at the apex is common in older animals and the pearly inner layer of the shell can show through.

The animal itself is mostly pink in colour. Two stalked eyes and a pair of sensory tentacles are located on the head above a well developed snout. The grey muscular foot lies underneath and slightly ventral to the head. Three pairs of sensory tentacles are present on the outside of the foot and are extended when the animal is active (Crothers 2001).

Also commonly known as the toothed top shell. Irregular damage lines may be visible on the shell if the animal has experienced environmental shock or has been attacked by predators.


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©  The Marine Biological Association of the United Kingdom

Source: Marine Life Information Network

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