BIOTIC

BIOTIC Species Information for Thyasira gouldi

Researched by

Angus Jackson

Data supplied by

MarLIN

Refereed by

This information is not refereed.

Taxonomy

Scientific name

Thyasira gouldi

Common name

Northern hatchet shell

MCS Code

W1838

Recent Synonyms

None

Phylum

Mollusca

Subphylum

Superclass

Class

Pelecypoda

Subclass

Order

Veneroida

Suborder

Family

Thyasiridae

Genus

Thyasira

Species

gouldi

Subspecies

Additional Information

The 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 form

Bivalved

Feeding method

Symbiont contribution
Active suspension feeder

Mobility/Movement

Burrower

Environmental position

Infaunal

Typical food types

Suspended organic matter and digestion of mutualistic bacteria.

Habit

Burrow dwelling

Bioturbator

Flexibility

None (< 10 degrees)

Fragility

Intermediate

Size

Very small(<1cm)

Height

Insufficient information

Growth Rate

1 mm/year

Adult dispersal potential

Not researched

Dependency

Mutualist with/on/in

Sociability

Solitary

Toxic/Poisonous?

General Biology Additional Information

Thyasira 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 & 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.

Biogeographic range

Not researched

Depth range

15-25m

Migratory

Non-migratory / Resident

Distribution Additional 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 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 preferences

Muddy sand
Mud
Sandy mud

Physiographic preferences

Sealoch

Biological zone

Lower Infralittoral
Upper Circalittoral
Lower Circalittoral

Wave exposure

Insufficient information

Tidal stream strength/Water flow

Insufficient information

Salinity

Reduced (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 type

Gonochoristic

Developmental mechanism

Direct Development

Reproductive Season

Year round

Reproductive Location

Sediment surface

Reproductive frequency

Annual protracted

Regeneration potential

Life span

Insufficient information

Age at reproductive maturity

Insufficient information

Generation time

Insufficient information

Fecundity

Up to 750 eggs per spawn

Egg/propagule size

Ca 260 µm long

Fertilization type

Internal

Larvae/Juveniles
Larval/Juvenile dispersal potential	<10m	Larval settlement period	Not relevant
Duration of larval stage	Not relevant

Reproduction Preferences Additional 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 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,