Lucinidae

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Lucinidae
Temporal range: Silurian - recent
File:Divaricella huttoniana (rotated).jpg
Divaricella huttoniana
Scientific classification
Kingdom:
Animalia
Phylum:
Mollusca
Class:
Bivalvia
Subclass:
Heterodonta
Order:
Veneroida
Superfamily:
Lucinoidea
Family:
Lucinidae

Fleming, 1828
Genera

See text

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Lucinidae is a family of saltwater clams, marine bivalve molluscs.

These bivalves are remarkable for their endosymbiosis with sulphide-oxidizing bacteria.[1]

Characteristics

The members of this family are found in muddy sand or gravel at or below low tide mark. They have characteristically rounded shells with forward-facing projections. The valves are flattened and etched with concentric rings. Each valve bears two cardinal and two plate-like lateral teeth. These molluscs do not have siphons but the extremely long foot makes a channel which is then lined with slime and serves for the intake and expulsion of water.[2]

Symbiosis

Lucinids host their sulfur-oxidizing symbionts in specialized gill cells called bacteriocytes.[3] Lucinids are burrowing bivalves that live in environments with sulfide-rich sediments.[4] The bivalve will pump sulfide-rich water over its gills from the inhalant siphon in order to provide symbionts with sulfur and oxygen.[4] The endosymbionts then use these substrates to fix carbon into organic compounds, which are then transferred to the host as nutrients.[5] During periods of starvation, lucinids may harvest and digest their symbionts as food.[5]

Symbionts are acquired via phagocytosis of bacteria by bacterioctyes.[6] Symbiont transmission occurs horizontally, where juvenile lucinids are aposymbiotic and acquire their symbionts from the environment in each generation.[7] Lucinids maintain their symbiont population by reaquiring sulfur-oxidizing bacteria throughout their lifetime.[8] Although process of symbiont acquisition is not entirely characterized, it likely involves the use of the binding protein, Codakine, isolated from the lucinid bivalve, Codaki orbicularis.[9] It is also known that symbionts do not replicate within bacteriocytes because of inhibition by the host. However, this mechanism is not well understood.[8]

Lucinid bivalves originated in the Silurian, however, they did not diversify until the late Cretaceous along with the evolution of seagrass meadows and mangrove swamps.[10] Lucinids were able to colonize these sulfide rich sediments because they already maintained a population of sulfide-oxidizing symbionts. In modern environments, seagrass, lucinid bivalves, and the sulfur-oxidizing symbionts constitute a three-way symbiosis. Because of the lack of oxygen in coastal marine sediments, dense seagrass meadows produce sulfide-rich sediments by trapping organic matter that is later decomposed by sulfate-reducing bacteria.[11] The lucinid-symbiont holobiont removes toxic sulfide from the sediment, and the seagrass roots provide oxygen to the bivalve-symbiont system.[11]

Genera and species

The species and genera include:

References

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  • ↑ Lua error in package.lua at line 80: module 'strict' not found.
  • ↑ Barrett, J. H. and C. M. Yonge, 1958. Collins Pocket Guide to the Sea Shore. P. 161. Collins, London
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