Lucinidae is a family of saltwater shells, marine bivalves mollusks.
These bivalves are remarkable for their endosymbiosis with sulfide oxidizing bacteria.
Video Lucinidae
Characteristics
These family members are found in muddy sand or gravel at or below the low tide marks. They have a round shell with front-facing projection. The valve is flattened and etched with concentric rings. Each valve produces two laterally cardinal-shaped teeth and two plates. This mollusc does not have a chiffon but very long legs make a channel which is then coated with mucus and serves for intake and water expulsion.
Maps Lucinidae
Symbiosis
Lucinids host their sulfur-oxidation symbionts in specialized gill cells called bacteriocytes. Lucinids are bivalve diggers that live in environments with rich sulphide sediments. Bivalve will pump sulphide-rich water above its gills from inhaled siphon to provide symbionts with sulfur and oxygen. Endosymbionts then use this substrate to fix carbon into organic compounds, which are then transferred to the host as nutrients. During periods of hunger, lucinids can harvest and digest their symbionts as food.
Symbionts are obtained by bacterial phagocytosis by bacteriocites. Symbiont transmission occurs horizontally, where juvenile lucinids are aposymbiotic and gain their symbionts from the environment in each generation. Lucinids retain their symbiont populations by reacquiring sulfur-oxidizing bacteria throughout their lifetime. Although the acquisition process of the symbionts is not fully characterized, it may involve the use of binding proteins, codakine, isolated from bivalvia lucinid, Codakia orbicularis . Also note that symbionts do not replicate in bacteriocytes due to host inhibition. However, this mechanism is not well understood.
Bivalvia Lucinid is from Silurian; however, they did not diversify until the final Cretaceous, along with the evolution of seagrass and mangrove swamps. Lucinids are able to colonize these sulphide-rich sediments because they have retained the oxidation-oxidation symbiosis population. In modern environments, seagrass, bivalvia lucinid, and sulfur-oxidation symbionts are three-way symbiosis. Due to the lack of oxygen in coastal marine sediments, seagrass seagrasses produce sulfide-rich sediments by trapping organic materials that are then broken down by sulphate reducing bacteria. The holiniont lucinid-symbiont removes toxic sulphides from the sediments, and the seagrass roots provide oxygen to the bivalve-symbiont system.
The symbionts of at least two species of lucinid shells, Codakia orbicularis and Loripes lucinalis , are able to fix nitrogen gas to organic nitrogen.
Genera and species
Source of the article : Wikipedia
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