Northern hatchet shell (Thyasira gouldii)
External view of Thyasira gouldii valve.
Photographer: National Museum Wales Copyright: Amgueddfa Cymru - Museum Wales
Distribution data supplied by the Ocean Biodiversity Information System (OBIS). To interrogate UK data visit the NBN Atlas.Map Help
| Researched by | Angus Jackson | Refereed by | This information is not refereed |
| Authority | (Philippi, 1845) | ||
| Other common names | - | Synonyms | - |
Summary
Description
A small, rather globular, white burrowing bivalve. The two halves of the shell are the same shape and the shell itself is thin and fragile. This species is very similar to Thyasira flexuosa, the wavy hatchet shell.
Recorded distribution in Britain and Ireland
At the head of Loch Etive, west coast of Scotland. Formerly also found in Lochs Linnhe, Eil and Sunart. Recorded also from Shetland (further detail lacking). Presence in Scottish waters forms the extreme southern end of the geographic range.Global distribution
A pan-arctic distribution from waters of the Commonwealth of Independent States along the north coast of Norway, around the coast of Greenland. On American coasts as far south as Cape Cod on the east and California on the west coast.Habitat
Inhabits a small chamber in the top few centimetres of soft mud or sand-mud sediments at the head of some sea lochs. Habitat generally characterized by the presence of organic matter.Depth range
15-25Identifying features
- A small, white, globular bivalve.
- The shell is equivalved but thin and fragile.
- The hinge line is without teeth.
- The inside of the shell is white and muscle scars indistinct.
- The gills are thick, fleshy and dark brown in colour.
Additional information
The larger eggs and characteristic sperm are useful features for separating Thyasira gouldii from Thyasira flexuosa.
Listed by
Biology review
Taxonomy
| Phylum | Mollusca | Snails, slugs, mussels, cockles, clams & squid |
| Class | Bivalvia | Clams, cockles, mussels, oysters, and scallops |
| Order | Lucinida | |
| Family | Thyasiridae | |
| Genus | Thyasira | |
| Authority | (Philippi, 1845) | |
| Recent Synonyms | ||
Biology
| Typical abundance | Moderate density | ||
| Male size range | up to 8mm | ||
| Male size at maturity | 4mm | ||
| Female size range | 4mm | ||
| Female size at maturity | |||
| Growth form | Bivalved | ||
| Growth rate | 1mm/year | ||
| Body flexibility | None (less than 10 degrees) | ||
| Mobility | |||
| Characteristic feeding method | Active suspension feeder, Non-feeding | ||
| Diet/food source | |||
| Typically feeds on | suspended organic matter and digestion of mutualistic bacteria. | ||
| Sociability | |||
| Environmental position | Infaunal | ||
| Dependency | Mutualist (Mutualism). a bacterium. | ||
| Supports | Host the parasitic copepod Axinophylus thyasirae and a mutualistic bacterium. | ||
| Is the species harmful? | No | ||
Biology information
Thyasira gouldii has been found up to 1,500 individuals per square metre but typically below 500. Such abundances may no longer exist in Scottish waters. It is difficult to define an adult size range as there appears no specific point where juveniles become adult. Values provided are roughly maximum size where size refers to shell length. Large numbers of a mutualistic bacterium live sub-cuticularly in the gills of Thyasira gouldii (and several other thyasirids). The bacteria are chemoautotrophic and oxidise sulphur in order to assimilate carbon dioxide. Carbon isotope ratios indicate that digestion of these bacteria contributes considerably to the nutrition of this species. Although the bacteria utilise sulphur the bivalves inhabit sediment with very little free sulphide. The relationship is not thought to be obligate but the presence of the bacterium is very beneficial to the brachiopod. Eleven percent of a population of Thyasira gouldii in Loch Etive was infected with the parasitic copepod Axinophylus thyasirae Blacknell & Ansell, 1975). This parasite inhabits the mantle cavity and causes lower body weights and indirect castration. The female parasites reach sizes of 4.5 mm and there can be up to five parasites per host causing massive restriction of the cavity and interfering with feeding currents.
Habitat preferences
| Physiographic preferences | Sea loch / Sea lough |
| Biological zone preferences | Lower circalittoral, Lower infralittoral, Upper circalittoral |
| Substratum / habitat preferences | Mud, Muddy sand, Sandy mud |
| Tidal strength preferences | |
| Wave exposure preferences | |
| Salinity preferences | Reduced (18-30 psu) |
| Depth range | 15-25 |
| Other preferences | No text entered |
| Migration Pattern | Non-migratory / resident |
Habitat Information
Geographic distribution was probably more general during the last glaciation and remaining populations are relicts. The populations in Lochs Linnhe and Eil have been killed by the discharge of pulp-mill effluent. The population in Loch Etive has also decreased massively between 1984 and 1989. It is possible that this decrease has been brought about by a viral infection of the mutualistic bacteria living on the gills of Thyasira gouldii. Digestion of the bacteria provides considerable nutrient input. This species can burrow up to ten times its shell length (max. 8cm) and uses its vermiform foot to create channels deeper into the sediment. A mucus lined inhalant tube is made up to the surface from the living chamber. Little information is available about preferred water flow rates but are probably quite low being at the head of a sea loch. Wave exposure preferences are also likely to be sheltered. Typical depths in Scottish waters are 15-25 metres but the species has been found down to a few hundred metres depth. Optimal salinity levels are 25-30 psu. Thyasira gouldii appears to be restricted to locations where bottom waters remain cool throughout the year as a result of salinity stratification.Life history
Adult characteristics
| Reproductive type | Gonochoristic (dioecious) | |
| Reproductive frequency | Annual protracted | |
| Fecundity (number of eggs) | 100-1,000 | |
| Generation time | Insufficient information | |
| Age at maturity | Insufficient information | |
| Season | January - December | |
| Life span | Insufficient information |
Larval characteristics
| Larval/propagule type | - |
| Larval/juvenile development | Direct development |
| Duration of larval stage | Not relevant |
| Larval dispersal potential | <10 m |
| Larval settlement period | Not relevant |
Life history information
The sexes are separate and fertilization probably occurs in the mantle or suprabranchial cavity. Egg development is temperature dependent being (in the laboratory) around 50 days at 10 degrees C and 37 days at 16 degrees C. There is no synchronisation of reproduction and spawning occurs throughout the year. Eggs are white, oval and about 260 microns long. Up to 750 eggs are produced with each spawning. No information is available on the mechanism of spawning or the number of spawnings per year. Fertilised eggs are 'pumped' out of the inhalant tube and being quite dense, sink down onto and stick to the sediment about 1 cm from the opening. Consequently eggs are rarely dispersed by water currents. No information is available about lifespan but given the known growth rate and maximum size achieved it must be at least 5-10 years.Sensitivity review
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
| Intolerance | Recoverability | Sensitivity | Evidence/Confidence | |
| High | Very low / none | Very High | Low | |
| The adults bury in the sediment so sediment loss would result in death. Populations in Scotland are isolated from each other. Development is direct without a planktonic stage, eggs are deposited next to the adult so larval dispersal is very limited. The populations are at the southern extreme of the species range and so may be already stressed by temperature or salinity variation. Recovery may not be possible. | ||||
| Low | Very high | Very Low | Low | |
| The species is an active burrower down to 8cm. Smothering with a further 5 cm sediment should not cause mortality. The bivalve would be able use its vermiform foot to burrow back up towards the surface. Spawning occurs throughout the year so once the factor is removed, feeding, burrowing and reproduction can resume as normal. | ||||
| Low | Very high | Very Low | Low | |
| Changes in siltation would probably not have a great effect on Thyasira gouldi. Feeding depends on the presence of suspended organic matter - decreases in siltation may reduce the food available, increases may facilitate feeding. Large increases in siltation may block up the inhalant tube which would require energetic expenditure to clear. Spawning occurs throughout the year so once the factor is removed, feeding, burrowing and reproduction can resume as normal. | ||||
| No information | ||||
| High | Very low / none | Very High | Low | |
| The species in entirely subtidal and breathes using gills. It is likely to be highly intolerant of desiccating influences. Populations in Scotland are isolated from each other. Development is direct without a planktonic stage, eggs are deposited next to the adult so larval dispersal is very limited. The populations are at the southern extreme of the species range and so may be already stressed by temperature or salinity variation. Recovery may not be possible. | ||||
| High | Very High | Low | ||
| The species in entirely subtidal and breathes using gills. It is likely to be highly intolerant of emergence. Populations in Scotland are isolated from each other. Development is direct without a planktonic stage, eggs are deposited next to the adult so larval dispersal is very limited. The populations are at the southern extreme of the species range and so may be already stressed by temperature or salinity variation. Recovery may not be possible. | ||||
| No information | ||||
| Low | Very high | Very Low | Low | |
| Increases in water flow may cause sediment movement, blocking the inhalant tube requiring energetic expenditure to clear. Spawning occurs throughout the year so once the factor is removed, feeding, burrowing and reproduction can resume as normal. | ||||
| No information | ||||
| High | Very High | Moderate | ||
| The populations in the British Isles are at the southern extreme of the geographical distribution. The surviving relict populations are restricted to areas where the bottom waters remain cool all year round. Any increases in temperature are likely to cause death. Populations in Scotland are isolated from each other. Development is direct without a planktonic stage, eggs are deposited next to the adult so larval dispersal is very limited. The populations are at the southern extreme of the species range and so may be already stressed by temperature or salinity variation. Recovery may not be possible. | ||||
| No information | ||||
| Tolerant | Not relevant | Not sensitive | Low | |
| This species is infaunal and as such will be tolerant of changes in turbidity. | ||||
| No information | ||||
| High | Very High | Low | ||
| Thyasira gouldi lives in rather wave sheltered areas at the heads of sealochs. Increases in wave exposure may disrupt the sediment in which they live, cause continual displacement and physical damage to the shells which are thin and fragile. Populations in Scotland are isolated from each other. Development is direct without a planktonic stage, eggs are deposited next to the adult so larval dispersal is very limited. The populations are at the southern extreme of the species range and so may be already stressed by temperature or salinity variation. Recovery may not be possible. | ||||
| No information | ||||
| Tolerant | Not relevant | Not sensitive | Very low | |
| This species probably has very limited facility for detection of vibrations. | ||||
| Tolerant | Not relevant | Not sensitive | Low | |
| This species is infaunal and probably has very limited facility for visual perception. | ||||
| High | Very High | Low | ||
| Thyasira gouldi is a small species and the shell is thin and fragile. They occupy the top few centimetres of the sediment and physical disturbance by a passing scallop dredge is likely to cause death Therefore, an intolerance of high has been recorded.
Populations in Scotland are isolated from each other. Development is direct without a planktonic stage, eggs are deposited next to the adult so larval dispersal is very limited. The populations are at the southern extreme of the species range and so may be already stressed by temperature or salinity variation. Recovery may not be possible. | ||||
| Low | Very high | Very Low | Low | |
| Thyasira gouldi are active burrowers, displacement will probably result in the bivalve burrowing back down into the sediment and creating a new living chamber and mucous lined inhalant siphon. There would be an energetic cost to this and feeding would be impaired. Spawning occurs throughout the year so once the factor is removed, feeding, burrowing and reproduction can resume as normal. | ||||
Chemical pressures
| Intolerance | Recoverability | Sensitivity | Evidence/Confidence | |
| No information | No information | No information | Not relevant | |
| Insufficient information | ||||
| No information | No information | No information | Not relevant | |
| Insufficient information | ||||
| No information | No information | No information | Not relevant | |
| Insufficient information | ||||
| No information | No information | No information | Very low | |
| Insufficient information | ||||
| High | Very High | Moderate | ||
| Organic enrichment from pulp mills is believed to have been the cause of the death of two populations in west Scotland sealochs. Similar species such as Thyasira flexuosa may be considerably more tolerant of nutrient enrichment (densities of up to 4000 per square metre have been recorded in areas or organic enrichment). Populations in Scotland are isolated from each other. Development is direct without a planktonic stage, eggs are deposited next to the adult so larval dispersal is very limited. The populations are at the southern extreme of the species range and so may be already stressed by temperature or salinity variation. Recovery may not be possible. | ||||
| Intermediate | Moderate | Moderate | Moderate | |
| The species inhabits waters of reduced salinity with 25-30 psu being optimal. Adults exposed to lower than optimal salinities produced non viable or slow developing eggs. There is insufficient information regarding the effects of salinity on adults. Development is direct without a planktonic stage, eggs are deposited next to the adult so larval dispersal is very limited. Immigration from other populations is highly unlikely. Reproduction occurs throughout the year, development is direct with quite high fecundity (750 eggs / spawning) High densities of the species are known to occur (up to 1500 per square metre). Growth however is rather slow (1mm/yr) and maturity is only reached at around 4 mm. Recruitment from this population would allow the population to recover in five to ten years. | ||||
| No information | ||||
| Intermediate | Moderate | Moderate | Low | |
| The bivalve burrows in often black, anoxic sediment but the area surrounding the mollusc is oxygenated through water movement down the inhalant tube. If the water inhaled becomes de-oxygenated (for instance because of isolation of water masses ) some mortality is likely.. Development is direct without a planktonic stage, eggs are deposited next to the adult so larval dispersal is very limited. Immigration from other populations is highly unlikely. Reproduction occurs throughout the year, development is direct with quite high fecundity (750 eggs / spawning) High densities of the species are known to occur (up to 1500 per square metre). Growth however is rather slow (1mm/yr) and maturity is only reached at around 4 mm. Recruitment from the local population would allow the population to recover in five to ten years. | ||||
Biological pressures
| Intolerance | Recoverability | Sensitivity | Evidence/Confidence | |
| Intermediate | Moderate | Moderate | Moderate | |
| Viral infection of the mutualist bacterium living on the bivalve's gills has been suggested as the reason for a major decline in the Loch Etive population. Development is direct without a planktonic stage, eggs are deposited next to the adult so larval dispersal is very limited. Immigration from other populations is highly unlikely. Reproduction occurs throughout the year, development is direct with quite high fecundity (750 eggs / spawning) High densities of the species are known to occur (up to 1500 per square metre). Growth however is rather slow (1mm/yr) and maturity is only reached at around 4 mm. Recruitment from this population would allow the population to recover in five to ten years. | ||||
| No information | No information | No information | Not relevant | |
| Insufficient information | ||||
| Not relevant | Not relevant | Not relevant | Moderate | |
| It is extremely unlikely that this species will be extracted - it has no economic or interest value and is protected by the Wildlife and Countryside Act and is covered by a UK Biodiversity Action Plan. | ||||
| Not relevant | Not relevant | Not relevant | Moderate | |
| The larva has no known obligate partner species that are likely to be extracted. Benthic trawls or dredges for other species may damage or destroy the shells but the species is protected by the Wildlife and Countryside Act and is covered by a UK Biodiversity Action Plan. | ||||
Additional information
Importance review
Policy/legislation
| Wildlife & Countryside Act | Schedule 5, section 9 |
Status
| National (GB) importance | Nationally rare | Global red list (IUCN) category | - |
Non-native
| Native | - | ||
| Origin | - | Date Arrived | - |
Importance information
-none-Bibliography
Anonymous, 1999g. Northern hatchet shell (Thyasira gouldi). Species Action Plan. In UK Biodiversity Group. Tranche 2 Action Plans. English Nature for the UK Biodiversity Group, Peterborough., English Nature for the UK Biodiversity Group, Peterborough.
Blacknell, W. M. & Ansell, A. D., 1974. The direct development of bivalve Thyasira gouldi (Philippi). Thalassia Jugoslavica, 10, 23-43.
Blacknell, W. M. & Ansell, A. D., 1975. Features of the reproductive cycle of an arctic bivalve from a Scottish sea loch. Marine Ecology, Pubblicazioni Della Stazione Zoologica Di Napoli I, 39, Suppl., 26-52.
Bowden, J. & Heppel, D., 1973. Revised list of British Mollusca. 2. Unionacea - Cardiacea. Journal of Conchology, 26, 237-272.
Dando, P.R. & Southward, A.J., 1986. Chemoautotrophy in bivalve molluscs of the Genus Thyasira. Journal of the Marine Biological Association of the United Kingdom, 60, 915-929.
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.]
Southward, E.C. & Southward, A.J., 1991. Virus-like particles in the bacteria symbiotic in bivalve gills. Journal of the Marine Biological Association of the United Kingdom, 71, 37-45.
Southward, E.C., 1986. Gill symbionts in the Thyasirids and other bivalve molluscs. Journal of the Marine Biological Association of the United Kingdom, 66, 889-914.
Tebble, N., 1966. British Bivalve Seashells. A Handbook for Identification. Edinburgh: British Museum (Natural History), Her Majesty's Stationary Office.
Datasets
NBN (National Biodiversity Network) Atlas. Available from: https://www.nbnatlas.org.
OBIS (Ocean Biodiversity Information System), 2023. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. www.iobis.org. Accessed: 2023-06-03
Citation
This review can be cited as:
Last Updated: 30/08/2007
