Biodiversity & Conservation

General Information

Thick top shell - Osilinus lineatus - General information

Image Keith Hiscock - Osilinus lineatus on intertidal rock. Image width ca 4 cm.
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Osilinus lineatus recorded () and expected () distribution in Britain and Ireland (see below)

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Osilinus lineatus is not listed under any importance categories.

General information

Researched by:	Nova Mieszkowska	Refereed by:	This information is not refereed.

Taxonomy

Phylum	Mollusca	Snails, slugs, mussels, cockles, clams & squid
Class	Gastropoda	Snails, slugs & sea butterflies

Recorded distribution in Britain and Ireland	Abundant on rocky shores in Britain reaching its northern limits on Anglesey & eastern limits at Osmington Mills, Dorset (pers. obs.). Absent from Scotland & the east coast of England. Range from Churchtown to Malin Head in Ireland.
Habitat information	Occurs in the midshore region of moderately exposed rocky shores in England and Wales. Requires a stable boulder field or broken shore with available bare rock.
Description	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).

Recorded distribution in Britain and Ireland

Abundant on rocky shores in Britain reaching its northern limits on Anglesey & eastern limits at Osmington Mills, Dorset (pers. obs.). Absent from Scotland & the east coast of England. Range from Churchtown to Malin Head in Ireland.

Habitat information

Occurs in the midshore region of moderately exposed rocky shores in England and Wales. Requires a stable boulder field or broken shore with available bare rock.

Description

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).

This review can be cited as follows:

Nova Mieszkowska 2008. Osilinus lineatus. Thick top shell. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 22/05/2013]. Available from: <http://www.marlin.ac.uk/speciesfullreview.php?speciesID=3990>

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