BIOTIC Species Information for Osilinus lineatus
Researched byNova Mieszkowska Data supplied byMarLIN
Refereed byThis information is not refereed.
Scientific nameOsilinus lineatus Common nameThick top shell
MCS CodeW177 Recent SynonymsMonodonta lineata
Trochocochlea lineata
Turbo lineatus

PhylumMollusca Subphylum
Superclass ClassGastropoda
SubclassProsobranchia OrderArchaeogastropoda
Suborder FamilyTrochidae
GenusOsilinus Specieslineatus

Additional InformationAlso 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.
Taxonomy References Howson & Picton, 1997, Hayward & Ryland, 1995b, Fish & Fish, 1996, Hayward et al., 1996, Crothers 2001, Desai, 1966, Fretter & Graham, 1977, Graham, 1988, Williamson & Kendall, 1981,
General Biology
Growth formTurbinate
Feeding methodHerbivore
Environmental positionEpilithic
Typical food typesMicroalgae HabitFree living
BioturbatorNot relevant FlexibilityNone (< 10 degrees)
FragilityRobust SizeSmall-medium(3-10cm)
HeightUp to 3 cm Growth RateSee additional information
Adult dispersal potential100-1000m DependencyIndependent
General Biology Additional InformationGrowth Rate
Initially rapid, Osilinus lineatus can grow up to 7-8mm in diameter between spawning and December (Fretter & Graham, 1977; Kendall et al.,1987), although the average size of newly settled animals is around 3mm (pers. obs.). Growth slows down and may stop in the first winter and every successive winter, before increasing in spring (Williams, 1965). One year post settlement, juveniles can reach 11-15mm (Fretter & Graham 1977, Fretter, 1988). Growth slows in adults when they become sexually mature but continues throughout the life of the animal.
Osilinus lineatus feeds on microscopic algae, which it grazes from rock surfaces using a brush-like radula on the tongue. Feeding is assumed to occur at night or during high water (Crothers, 2001) as no observations of feeding during daylight or at low water have been published.

Osilinus lineatus has a gill for respiration in water and a well vascularised mantle cavity which allows the animal to breathe in air (Crothers, 2001).

Osilinus lineatus detects its environment by means of two stalk eyes and a pair of sensory tentacles on the head, and three pairs of sensory tentacles on the foot.

Biology References Hawkins & Jones, 1992, Fish & Fish, 1996, Hayward et al., 1996, Crothers 2001, Desai, 1966, Fretter & Graham, 1977, Graham, 1988, Kendall et al., 1987, Williams, 1965., Williamson & Kendall, 1981,
Distribution and Habitat
Distribution in Britain & IrelandAbundant 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.
Global distributionFound in the north eastern Atlantic from Morocco to Cap de la Hague, France on mainland Europe (Crisp & Southward, 1958; Fretter & Graham 1977). Northern limits reached in North Wales and North Ireland.
Biogeographic rangeNot researched Depth rangeMHWS to MLWS
MigratorySeasonal (reproduction)   
Distribution Additional InformationOsilinus lineatus is widely distributed on rocky shores between the 20 °C summer isotherm off Africa and the 6.5 °C winter isotherm off Anglesey. Northern limits are primarily set by reproductive failure (Lewis et al., 1982; Lewis 1986; Kendall, 1986) but may also be determined by hydrography or unsuitable habitat (Crisp & Knight-Jones, 1953)

Juvenile Osilinus lineatus are found in nursery areas underneath boulders or in fissures. Adults crawl out of these damp areas onto the sides of boulders during warm, dry periods but tend to retreat to the lower surfaces of rocks when the weather is colder.

In early summer Osilinus lineatusadults migrate up shore to the high eulittoral prior to spawning. Once spawning has occurred the animals migrate back down shore to the mid to lower eulittoral zone to over-winter.

Substratum preferencesBedrock
Large to very large boulders
Under boulders
Physiographic preferencesOpen coast
Strait / sound
Enclosed coast / Embayment
Biological zoneUpper Eulittoral
Mid Eulittoral
Lower Eulittoral
Wave exposureExposed
Moderately Exposed
Tidal stream strength/Water flowStrong (3-6 kn)
Moderately Strong (1-3 kn)
SalinityVariable (18-40 psu)
Full (30-40 psu)
Habitat Preferences Additional Information
Distribution References Hawkins & Jones, 1992, Hayward & Ryland, 1995b, Fish & Fish, 1996, Hayward et al., 1996, JNCC, 1999, NBN, 2002, Picton & Costello, 1998, Desai, 1966, Fretter & Graham, 1977, Kendall, 1987, Crisp & Southward, 1958, Crisp & Knight-Jones, 1953, Lewis et al., 1982, Lewis, 1986, Boaden et al., 1964,
Reproduction/Life History
Reproductive typeGonochoristic
Developmental mechanismPlanktotrophic
Reproductive SeasonMay to August Reproductive LocationWater column
Reproductive frequencyAnnual protracted Regeneration potential No
Life span11-20 years Age at reproductive maturity1-2 years
Generation time3-5 years FecundityInsufficient information
Egg/propagule size165-250 µm eggs Fertilization typeExternal
Larval/Juvenile dispersal potentialInsufficient information Larval settlement periodInsufficient information
Duration of larval stage2-10 days   
Reproduction Preferences Additional InformationReproductive Cycle
Sexes are separate but the two sexes cannot be differentiated between by external examination (Fretter & Graham, 1977; Hickman, 1992).

Osilinus lineatus has five stages to its reproductive cycle (Ortonet al., 1956; Desai, 1966). Onset of gonad maturation has been correlated with rising sea temperatures.
Stage I Late summer the gonad is inactive. Both male and female gonads are brown in colour and appear as loose, sac-like structures. Any oocytes present are smaller than 25 µm in diameter.
Stage II. In October the ovaries and testis both take on a greenish hue. Oocytes of up to 50 micrometres are present in females and spermatogonia are present in males.
Stage III. In early January, ovaries and testis are green, oocytes have grown to diameters greater than 50 µm. Spermatocytes and spermatids are present in males.
Stage IV. In February to May, ovaries are deep green in pigment and contain a mixture of mature and immature oocytes. Testis become pink in colour and contain spermatozoa.
Stage V. In May, ovaries are deep green and distended, oocytes are mostly mature. Testis are pink/cream and contain fully active spermatozoa.
Adult Osilinus lineatusmigrate upshore to the high eulittoral zone in early summer prior to spawning. It is thought that this migration brings the animals into a region of higher temperature required for spawning. Desai (1966) found that adults that had migrated furthest upshore were the first to spawn, supporting this idea.
Osilinus lineatus is a broadcast spawner (Underwood, 1972; Hickman, 1992). Males release clouds of white spermatozoa into the water column and females undergo repeated spasms, releasing a few eggs at a time from the mantle cavity into the water (Fretter & Graham 1977). Fertilization occurs externally.

The breeding season is shorter near to northern range limits, with a single spawning period. Towards the centre of the range the breeding season is longer and multiple spawning events occur (Garwood & Kendall, 1985, Bode et al,1986).
Larval Development
Eggs of diameters between 165-250 µm are released individually (Desai, 1966; Fretter & Graham, 1994). The external jelly coating swells on contact with water, making the egg initially buoyant. After 20 minutes the jelly coating disintegrates and the egg sinks. The eggs are lecithotrophic (contain yolk) and provide food for larval development until the larvae hatch as free swimming veligers after 29-30 hours. Six days after fertilization the larva has grown to approximately 1mm in diameter and has fully developed its crawling ability (Desai 1966, Fretter & Graham 1977). Larvae settle on the shore in the low eulittoral zone under boulders and in cracks and crevices.
Reproduction References Garwood & Kendall, 1985, Fish & Fish, 1996, Desai, 1966, Hickman, 1992, Bodeet al., 1986, Fretter & Graham, 1994, Orton et al., 1956, Underwood, 1972, Lewis, 1986,
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