BIOTIC Species Information for Thyasira gouldi
Researched byAngus Jackson Data supplied byMarLIN
Refereed byThis information is not refereed.
Scientific nameThyasira gouldi Common nameNorthern hatchet shell
MCS CodeW1838 Recent SynonymsNone

PhylumMollusca Subphylum
Superclass ClassPelecypoda
Subclass OrderVeneroida
Suborder FamilyThyasiridae
GenusThyasira Speciesgouldi

Additional InformationThe larger eggs and characteristic sperm are useful features for separating Thyasira gouldi from Thyasira flexuosa.
Taxonomy References Howson & Picton, 1997, Blacknell & Ansell, 1975, Tebble, 1966, Southward, 1986, Blacknell & Ansell, 1974,
General Biology
Growth formBivalved
Feeding methodSymbiont contribution
Active suspension feeder
Environmental positionInfaunal
Typical food typesSuspended organic matter and digestion of mutualistic bacteria. HabitBurrow dwelling
Bioturbator FlexibilityNone (< 10 degrees)
FragilityIntermediate SizeVery small(<1cm)
HeightInsufficient information Growth Rate1 mm/year
Adult dispersal potentialNot researched DependencyMutualist with/on/in
General Biology Additional InformationThyasira gouldi 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 gouldi (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 gouldi 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.
Biology References Blacknell & Ansell, 1975, Southward, 1986, Blacknell & Ansell, 1974, Southward & Southward, 1991, Dando & Southward, 1986, Anonymous, 1999(g),
Distribution and Habitat
Distribution in Britain & IrelandAt 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 distributionA 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.
Biogeographic rangeNot researched Depth range15-25m
MigratoryNon-migratory / Resident   
Distribution Additional InformationGeographic 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 gouldi. 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 gouldi appears to be restricted to locations where bottom waters remain cool throughout the year as a result of salinity stratification.

Substratum preferencesMuddy sand
Sandy mud
Physiographic preferencesSealoch
Biological zoneLower Infralittoral
Upper Circalittoral
Lower Circalittoral
Wave exposureInsufficient information
Tidal stream strength/Water flowInsufficient information
SalinityReduced (18-30 psu)
Habitat Preferences Additional Information
Distribution References Blacknell & Ansell, 1975, Southward, 1986, Blacknell & Ansell, 1974, Bowden & Heppel, 1973, Southward & Southward, 1991, Dando & Southward, 1986,
Reproduction/Life History
Reproductive typeGonochoristic
Developmental mechanismDirect Development
Reproductive SeasonYear round Reproductive LocationSediment surface
Reproductive frequencyAnnual protracted Regeneration potential No
Life spanInsufficient information Age at reproductive maturityInsufficient information
Generation timeInsufficient information FecundityUp to 750 eggs per spawn
Egg/propagule sizeCa 260 µm long Fertilization typeInternal
Larval/Juvenile dispersal potential<10m Larval settlement periodNot relevant
Duration of larval stageNot relevant   
Reproduction Preferences Additional InformationThe 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 life span but given the known growth rate and maximum size achieved it must be at least 5-10 years.
Reproduction References Blacknell & Ansell, 1975, Blacknell & Ansell, 1974,
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