Looping snail (Truncatella subcylindrica)

One juvenile crawling shell and 5 adults of Truncatella subcylindrica. Also one shell of Paludinella litorina.

Photographer: Dennis R. Seaward Copyright: Dennis R. Seaward

Line drawing of Truncatella subcylindrica.

Photographer: Copyright: Dr R.S.K. Barnes

Two adult Truncatella subcylindrica, one crawling.

Photographer: Dennis R. Seaward Copyright: Dennis R. Seaward

Distribution data supplied by the Ocean Biodiversity Information System (OBIS). To interrogate UK data visit the NBN Atlas.Map Help

Researched by	Nicola White	Refereed by	Dennis R. Seaward
Researched by Nicola White	Refereed by Dennis R. Seaward
Authority	(Linnaeus, 1767)
Authority (Linnaeus, 1767)
Other common names	-	Synonyms	-
Other common names -	Synonyms -

Summary

Description

A buff-coloured snail that grows up to 5 mm high. The animal has a cylindrical snout ending in a rounded mouth disc. It has a peculiar looping gait.

Recorded distribution in Britain and Ireland

Recorded from Pagham Harbour, West Sussex; The Solent, Isle of Wight, The Fleet, Dorset and St Mawes Bay, Cornwall.

Global distribution

From the Channel coasts of France and Britain to the Mediterranean, the Black Sea, and on the Canaries, Madeira and Azores.

Habitat

Found in shingle amongst rotting vegetation and fine sediment at a depth of 15 cm, at high water mark and more rarely in muddy habitats under stones at the high water mark. It is often associated with the plants Suaeda maritima, Suaeda vera and Atriplex (Halimione) portulacoides.

Depth range

Identifying features

The juvenile has a typical spire-shaped shell; later whorls are parallel-sided until maturity when the tapered part is broken off, leaving a suture line. The adult shell is thus truncated and more or less cylindrical.
Buff-coloured, 5 mm high.
Animal with cylindrical snout ending in a rounded mouth disc.

Additional information

Abscission of the earlier part of the shell is presumably an adaptation to an interstial habitat.
The taxonomy of the Gastropoda has been recently revised (see Ponder & Lindberg 1997, and Taylor 1996). Ponder & Lindberg (1997) suggest that Mesogastropoda should be included in a monophyletic clade, the Caenogastropoda.

Listed by

- none -

Biology review

Taxonomy

Level	Scientific name	Common name
Phylum	Mollusca	Snails, slugs, mussels, cockles, clams & squid
Snails, slugs, mussels, cockles, clams & squid
Class	Gastropoda	Snails, slugs & sea butterflies
Snails, slugs & sea butterflies
Order	Littorinimorpha

Family	Truncatellidae
Genus	Truncatella
Authority	(Linnaeus, 1767)
Recent Synonyms

Biology

Parameter	Data
Typical abundance	Moderate density
Male size range	up to 5mm
Male size at maturity
Female size range	Very small(<1cm)
Female size at maturity
Growth form	Cylindrical
Growth rate	Data deficient
Body flexibility
Mobility	Creeper
Characteristic feeding method	Sub-surface deposit feeder, Surface deposit feeder
Diet/food source
Typically feeds on	Vegetable detritus and small algae
Sociability
Environmental position	Epifaunal
Dependency	Independent.
Supports	Not relevant
Is the species harmful?	Data deficient

Biology information

It has a peculiar looping gait and moves along by alternately attaching the foot and snout to the substratum (Seaward, 1988). The species is found at moderate densities in narrow, linear habitats.

Habitat preferences

Parameter	Data
Physiographic preferences	Estuary, Isolated saline water (Lagoon)
Biological zone preferences	Lower littoral fringe, Upper littoral fringe
Substratum / habitat preferences	Gravel / shingle, Mud
Tidal strength preferences	Very weak (negligible)
Wave exposure preferences	Sheltered
Salinity preferences	Variable (18-40 psu)
Depth range
Other preferences	No text entered
Migration Pattern	Non-migratory or resident

Habitat Information

Formerly known from 12 sites in Britain, from Porthcurno along the south coast to the rivers Orwell and Deben, Suffolk. Presently known to be living in only five locations. It is a southern species which reaches its most northerly distribution in Britain. Paludinella globularis (as littorina), Ovatella myosotis and Leucophytia bidentata are associates.

Life history

Adult characteristics

Parameter	Data
Reproductive type	Gonochoristic (dioecious)
Reproductive frequency	No information
Fecundity (number of eggs)	No information
Generation time	Insufficient information
Age at maturity	Insufficient information
Season	Insufficient information
Life span	Insufficient information

Larval characteristics

Parameter	Data
Larval/propagule type	-
Larval/juvenile development	Oviparous
Duration of larval stage	Not relevant
Larval dispersal potential	<10 m
Larval settlement period	Insufficient information

Life history information

Egg capsules are laid of 0.75-0.80mm diameter, which are spherical and surrounded by a thick wall. Each capsule contains one egg and they are attached singly to pieces of detritus in the habitat in which the adults live. Small snails are hatched with a shell of 0.65mm (Fretter & Graham, 1978)

Sensitivity reviewHow is sensitivity assessed?

The MarLIN sensitivity assessment approach used below has been superseded by the MarESA (Marine Evidence-based Sensitivity Assessment) approach (see menu). The MarLIN approach was used for assessments from 1999-2010. The MarESA approach reflects the recent conservation imperatives and terminology and is used for sensitivity assessments from 2014 onwards.

Physical pressures

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	Intolerance	Recoverability	Sensitivity	Evidence / Confidence
Substratum loss [Show more] Substratum loss Benchmark. All of the substratum occupied by the species or biotope under consideration is removed. A single event is assumed for sensitivity assessment. Once the activity or event has stopped (or between regular events) suitable substratum remains or is deposited. Species or community recovery assumes that the substratum within the habitat preferences of the original species or community is present. Further details Evidence The species would be removed with substratum loss and may be damaged during the process. It has low recoverability as it lacks an aquatic dispersal phase and living populations are only known from three locations in the UK.	High	Low	High	Very low
Smothering [Show more] Smothering Benchmark. All of the population of a species or an area of a biotope is smothered by sediment to a depth of 5 cm above the substratum for one month. Impermeable materials, such as concrete, oil, or tar, are likely to have a greater effect. Further details. Evidence Smothering could block shingle interstices and prevent movement of the snail and reduce the level of oxygenation. Recovery would be low because it lacks an aquatic dispersal phase and living populations are only known from five locations in the UK.	High	Low	High	Very low
Increase in suspended sediment [Show more] Increase in suspended sediment Benchmark. An arbitrary short-term, acute change in background suspended sediment concentration e.g., a change of 100 mg/l for one month. The resultant light attenuation effects are addressed under turbidity, and the effects of rapid settling out of suspended sediment are addressed under smothering. Further details Evidence Truncatella subcylindrica lives in estuaries and lagoons amongst fine muddy sediment so would be able to tolerate increased siltation. Indeed, some increased siltation may be beneficial to feeding as it is a deposit feeder, so long as interstices remain clear.	Tolerant*	Not relevant	Not sensitive*	Very low
Decrease in suspended sediment [Show more] Decrease in suspended sediment Benchmark. An arbitrary short-term, acute change in background suspended sediment concentration e.g., a change of 100 mg/l for one month. The resultant light attenuation effects are addressed under turbidity, and the effects of rapid settling out of suspended sediment are addressed under smothering. Further details Evidence			No information
Desiccation [Show more] Desiccation A normally subtidal, demersal or pelagic species including intertidal migratory or under-boulder species is continuously exposed to air and sunshine for one hour. A normally intertidal species or community is exposed to a change in desiccation equivalent to a change in position of one vertical biological zone on the shore, e.g., from upper eulittoral to the mid eulittoral or from sublittoral fringe to lower eulittoral for a period of one year. Further details. Evidence The mollusc is adapted to avoid desiccation by having a hard shell and operculum. Where it is interstitial, the species would also be protected from desiccation by the depth of sediment above it and where the species is epifaunal would avoid desiccation by hiding in crevices or under stones.	Low	Moderate	Low	Very low
Increase in emergence regime [Show more] Increase in emergence regime Benchmark. A one hour change in the time covered or not covered by the sea for a period of one year. Further details Evidence Increased or decreased emergence is likely to occur on a relatively long time scale, during which the habitat and animals will probably be able to re-adjust.	Low	Moderate	Low	Very low
Decrease in emergence regime [Show more] Decrease in emergence regime Benchmark. A one hour change in the time covered or not covered by the sea for a period of one year. Further details Evidence			No information
Increase in water flow rate [Show more] Increase in water flow rate A change of two categories in water flow rate (view glossary) for 1 year, for example, from moderately strong (1-3 knots) to very weak (negligible). Further details Evidence Living at high water mark, the species is inundated for only short periods, so that increased water flow is unlikely to have a significant effect unless it is so great as to erode materials and animals.	Low	Moderate	Low	Very low
Decrease in water flow rate [Show more] Decrease in water flow rate A change of two categories in water flow rate (view glossary) for 1 year, for example, from moderately strong (1-3 knots) to very weak (negligible). Further details Evidence			No information
Increase in temperature [Show more] Increase in temperature A short-term, acute change in temperature; e.g., a 5°C change in the temperature range for three consecutive days. This definition includes ‘short-term’ thermal discharges. A long-term, chronic change in temperature; e.g. a 2°C change in the temperature range for a year. This definition includes ‘long term’ thermal discharges. For intertidal species or communities, the range of temperatures includes the air temperature regime for that species or community. Further details Evidence The degree of temperature tolerance of Truncatella subcylindrica is not known. The species will be sheltered from temperature extremes to some extent by its hard shell and by its interstitial habitat. However, the species may be intolerant of decreases in temperature as it is at the northern limit of its distribution.	Intermediate	Moderate	Moderate	Very low
Decrease in temperature [Show more] Decrease in temperature A short-term, acute change in temperature; e.g., a 5°C change in the temperature range for three consecutive days. This definition includes ‘short-term’ thermal discharges. A long-term, chronic change in temperature; e.g. a 2°C change in the temperature range for a year. This definition includes ‘long term’ thermal discharges. For intertidal species or communities, the range of temperatures includes the air temperature regime for that species or community. Further details Evidence			No information
Increase in turbidity [Show more] Increase in turbidity A short-term, acute change; e.g., two categories of the water clarity scale (see glossary) for one month, such as from medium to extreme turbidity. A long-term, chronic change; e.g., one category of the water clarity scale (see glossary) for one year, such as from low to medium turbidity. Further details Evidence The species is unlikely to be affected by a change in turbidity as it does not depend on light availability for feeding and some populations are found interstitially where light cannot penetrate.	Tolerant	Not relevant	Not sensitive	Very low
Decrease in turbidity [Show more] Decrease in turbidity A short-term, acute change; e.g., two categories of the water clarity scale (see glossary) for one month, such as from medium to extreme turbidity. A long-term, chronic change; e.g., one category of the water clarity scale (see glossary) for one year, such as from low to medium turbidity. Further details Evidence			No information
Increase in wave exposure [Show more] Increase in wave exposure A change of two ranks on the wave exposure scale (view glossary) e.g., from Exposed to Extremely exposed for a period of one year. Further details Evidence The high water mark habitat means that the species is only subject to wave action for short periods. However, increased wave action may damage or wash it away, or move shingle damaging the animal by abrasion.	Intermediate	Low	High	Very low
Decrease in wave exposure [Show more] Decrease in wave exposure A change of two ranks on the wave exposure scale (view glossary) e.g., from Exposed to Extremely exposed for a period of one year. Further details Evidence			No information
Noise [Show more] Noise Underwater noise levels e.g., the regular passing of a 30-metre trawler at 100 metres or a working cutter-suction transfer dredge at 100 metres for one month during important feeding or breeding periods. Atmospheric noise levels e.g., the regular passing of a Boeing 737 passenger jet 300 metres overhead for one month during important feeding or breeding periods. Further details Evidence Insufficient information	No information	Not relevant	No information	Not relevant
Visual presence [Show more] Visual presence Benchmark. The continuous presence for one month of moving objects not naturally found in the marine environment (e.g., boats, machinery, and humans) within the visual envelope of the species or community under consideration. Further details Evidence Insufficient information	No information	Not relevant	No information	Not relevant
Abrasion & physical disturbance [Show more] Abrasion & physical disturbance Benchmark. Force equivalent to a standard scallop dredge landing on or being dragged across the organism. A single event is assumed for assessment. This factor includes mechanical interference, crushing, physical blows against, or rubbing and erosion of the organism or habitat of interest. Where trampling is relevant, the evidence and trampling intensity will be reported in the rationale. Further details. Evidence Any factor causing movement of shingle where the animal lives, by natural (e.g. wave action) or human (e.g. trampling) means would be likely to damage infauna by abrasion and crushing.	High		Very High	Very low
Displacement [Show more] Displacement Benchmark. Removal of the organism from the substratum and displacement from its original position onto a suitable substratum. A single event is assumed for assessment. Further details Evidence Habitat displacement would cause damage to animals.	High	Low	High	Very low

Chemical pressures

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	Intolerance	Recoverability	Sensitivity	Evidence / Confidence
Synthetic compound contamination [Show more] Synthetic compound contamination Sensitivity is assessed against the available evidence for the effects of contaminants on the species (or closely related species at low confidence) or community of interest. For example: evidence of mass mortality of a population of the species or community of interest (either short or long term) in response to a contaminant will be ranked as high sensitivity; evidence of reduced abundance, or extent of a population of the species or community of interest (either short or long term) in response to a contaminant will be ranked as intermediate sensitivity; evidence of sub-lethal effects or reduced reproductive potential of a population of the species or community of interest will be assessed as low sensitivity. The evidence used is stated in the rationale. Where the assessment can be based on a known activity then this is stated. The tolerance to contaminants of species of interest will be included in the rationale when available; together with relevant supporting material. Further details. Evidence Exposure of spermatocytes of the species to dibutyltin(IV) and tributyltin(IV) caused structural damage in the chromosomes in 24 hours at 0.0001 moles per litre (Vitturi et al., 1992).	High	Low	High	Moderate
Heavy metal contamination [Show more] Heavy metal contamination Evidence Insufficient information	No information	Not relevant	No information	Not relevant
Hydrocarbon contamination [Show more] Hydrocarbon contamination Evidence Insufficient information	No information	Not relevant	No information	Not relevant
Radionuclide contamination [Show more] Radionuclide contamination Evidence Insufficient information	No information	Not relevant	No information	Not relevant
Changes in nutrient levels [Show more] Changes in nutrient levels Evidence Insufficient information	No information	Not relevant	No information	Not relevant
Increase in salinity [Show more] Increase in salinity A short-term, acute change; e.g., a change of two categories from the MNCR salinity scale for one week (view glossary) such as from full to reduced. A long-term, chronic change; e.g., a change of one category from the MNCR salinity scale for one year (view glossary) such as from reduced to low. Further details. Evidence The species occurs in lagoons and estuaries so is tolerant of reduced and fully saline conditions. However, the species may not be tolerant of low salinities for long periods of time.	Low	Low	Moderate	Very low
Decrease in salinity [Show more] Decrease in salinity A short-term, acute change; e.g., a change of two categories from the MNCR salinity scale for one week (view glossary) such as from full to reduced. A long-term, chronic change; e.g., a change of one category from the MNCR salinity scale for one year (view glossary) such as from reduced to low. Further details. Evidence			No information
Changes in oxygenation [Show more] Changes in oxygenation Benchmark. Exposure to a dissolved oxygen concentration of 2 mg/l for one week. Further details. Evidence Insufficient information	No information	Not relevant	No information	Not relevant

Biological pressures

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	Intolerance	Recoverability	Sensitivity	Evidence / Confidence
Introduction of microbial pathogens/parasites [Show more] Introduction of microbial pathogens/parasites Benchmark. Sensitivity can only be assessed relative to a known, named disease, likely to cause partial loss of a species population or community. Further details. Evidence Insufficient information	No information	Not relevant	No information	Not relevant
Introduction of non-native species [Show more] Introduction of non-native species Sensitivity assessed against the likely effect of the introduction of alien or non-native species in Britain or Ireland. Further details. Evidence Insufficient information	No information	Not relevant	No information	Not relevant
Extraction of this species [Show more] Extraction of this species Benchmark. Extraction removes 50% of the species or community from the area under consideration. Sensitivity will be assessed as 'intermediate'. The habitat remains intact or recovers rapidly. Any effects of the extraction process on the habitat itself are addressed under other factors, e.g. displacement, abrasion and physical disturbance, and substratum loss. Further details. Evidence NR	Not relevant	Not relevant	Not relevant	Not relevant
Extraction of other species [Show more] Extraction of other species Benchmark. A species that is a required host or prey for the species under consideration (and assuming that no alternative host exists) or a keystone species in a biotope is removed. Any effects of the extraction process on the habitat itself are addressed under other factors, e.g. displacement, abrasion and physical disturbance, and substratum loss. Further details. Evidence Would cause huge disturbance and damage but is unlikely.	High	Low	High	Very low

Additional information

Importance review

Policy/legislation

Designation	Support

Status

National (GB) importance	Not rare or scarce	Global red list (IUCN) category	-
National (GB) importance Not rare or scarce
Global red list (IUCN) category -

Non-native

Parameter	Data
Native	-
Origin	-
Date Arrived	-

Importance information

The assemblage is of low diversity and biomass occupying only a small proportion of the space available. It is unlikely to provide a unique food source, although a nemertean predator Prosorhochmus claparedii is recorded from the same niche at the Fleet (R.S.K. Barnes, per. comm.)

Bibliography

Barnes, R.S.K., 1994. The brackish-water fauna of northwestern Europe. Cambridge: Cambridge University Press.
Fretter, V., & Graham, A., 1978. The Prosobranch Molluscs of Britain and Denmark. Part 3. Journal of Molluscan Studies, Supplement 5, 137.
Howson, C.M. & Picton, B.E., 1997. The species directory of the marine fauna and flora of the British Isles and surrounding seas. Belfast: Ulster Museum. [Ulster Museum publication, no. 276.]
Killeen, I.J. & Light, J.M., 1998. A discovery of Truncatella subcylindrica living in Cornwall. Journal of Conchology, 36, 50-51.
Ponder, W.F. & Lindberg, D.R., 1997. Towards a phylogeny of gastropod molluscs: an analysis using morphological characters. Zoological Journal of the Linnean Society, 119, 83-265.
Seaward, D.R., 1988. Locomotion in Truncatella subcylindrica. Journal of Conchology, 33, 49.
Seaward, D.R., 1991. Caecum armoricum. In British Red Data Book. 3. Invertebrates other than Insects (ed. J.H. Bratton). Peterborough: Joint Nature Conservation Committee. 253p.
Taylor, J.D.(ed.), 1996. Origin and Evolutionary Radiation of the Mollusca. Oxford: Oxford University Press.
Vitturi, R., Mansueto, C., Catalano, E., Pellerito, L., & Girasolo, M.A., 1992. Spermatocyte chromosome alterations in Truncatella subcylindrica following exposure to dibutyltin (IV) and tributyltin(IV) chlorides Applied Organometallic Chemistry, 6, 525-532.

Datasets

Conchological Society of Great Britain & Ireland, 2017. Mollusc (non-marine): 1999 Atlas Dataset for Great Britain and Ireland. Occurrence dataset: https://doi.org/10.15468/gbawsj accessed via GBIF.org on 2018-09-25.
Conchological Society of Great Britain & Ireland, 2017. Mollusc (non-marine): Compilation of records of rare and scarce species for Great Britain and Northern Ireland. Occurrence dataset: https://doi.org/10.15468/e9fnjh accessed via GBIF.org on 2018-09-25.
Conchological Society of Great Britain & Ireland, 2018. Mollusc (marine) data for Great Britain and Ireland - restricted access. Occurrence dataset: https://doi.org/10.15468/4bsawx accessed via GBIF.org on 2018-09-25.
Conchological Society of Great Britain & Ireland, 2018. Mollusc (non-marine) data for Great Britain and Ireland. Occurrence dataset: https://doi.org/10.15468/6dexp9 accessed via GBIF.org on 2018-09-25.
Conchological Society of Great Britain & Ireland, 2023. Mollusc (marine) records for Great Britain and Ireland. Occurrence dataset: https://doi.org/10.15468/aurwcz accessed via GBIF.org on 2024-09-27.
Kent & Medway Biological Records Centre, 2017. Land molluscs: Records for Kent. Occurrence dataset: https://doi.org/10.15468/zintf2 accessed via GBIF.org on 2018-10-01.
Kent Wildlife Trust, 2018. Kent Wildlife Trust Shoresearch Intertidal Survey 2004 onwards. Occurrence dataset: https://www.kentwildlifetrust.org.uk/ accessed via NBNAtlas.org on 2018-10-01.
NBN (National Biodiversity Network) Atlas. Available from: https://www.nbnatlas.org.
OBIS (Ocean Biodiversity Information System), 2025. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. www.iobis.org. Accessed: 2025-05-21

Citation

This review can be cited as:

White, N. 2008. Truncatella subcylindrica Looping snail. In Tyler-Walters H. Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 21-05-2025]. Available from: https://www.marlin.ac.uk/species/detail/1206

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Last Updated: 03/06/2008

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