Lucinidae, common name hatchet shells, is a

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

of saltwater

clam Clam is a common name for several kinds of bivalve molluscs. The word is often applied only to those that are edible and live as infauna, spending most of their lives halfway buried in the sand of the seafloor or riverbeds. Clams have two shel ...

s, marine bivalve

molluscs Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is estim ...

. These bivalves are remarkable for their

endosymbiosis An ''endosymbiont'' or ''endobiont'' is any organism that lives within the body or cells of another organism most often, though not always, in a mutualistic relationship. (The term endosymbiosis is from the Greek: ἔνδον ''endon'' "within ...

with sulphide-oxidizing

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...

Characteristics

The members of this family have a worldwide distribution. They are found in muddy sand or gravel at or below low tide mark. But they can also be found at bathyal depths. They have characteristically rounded shells with forward-facing projections. The shell is predominantly white and buff and is often thin-shelled. The shells are equivalve with unequal sides. The umbones (the apical part of each valve) are just anterior to mid-line. The adductor scars are unequal: the anterior are narrower and somewhat longer than the posterior. They are partly or largely separated from the pallial line. The valves are flattened and etched with concentric or radial 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. The ligament is external and is often deeply inset. The pallial line lacks a sinus.

Fossil record

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...

species '' Superlucina megameris'' was the largest lucinid ever recorded, with shell size up to high, over wide and thick.

Symbiosis

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

phagocytosis Phagocytosis () is the process by which a cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs phagocytosis is ...

of bacteria by bacterioctyes. Symbiont transmission occurs horizontally, where juvenile lucinids are aposymbiotic and acquire their symbionts from the environment in each generation. Lucinids maintain their symbiont population by reacquiring sulfur-oxidizing bacteria throughout their lifetime. Although process of symbiont acquisition is not entirely characterized, it likely involves the use of the binding protein, codakine, isolated from the lucinid bivalve, ''Codakia orbicularis''. It is also known that symbionts do not replicate within bacteriocytes because of inhibition by the host. However, this mechanism is not well understood. Lucinid bivalves originated in the Silurian; however, they did not diversify until the late

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

, along with the evolution of

seagrass meadow A seagrass meadow or seagrass bed is an underwater ecosystem formed by seagrasses. Seagrasses are marine (saltwater) plants found in shallow coastal waters and in the brackish waters of estuaries. Seagrasses are flowering plants with stems and ...

s and mangrove swamps. 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. The lucinid-symbiont

holobiont A holobiont is an assemblage of a host and the many other species living in or around it, which together form a discrete ecological unit through symbiosis, though there is controversy over this discreteness. The components of a holobiont are i ...

removes toxic sulfide from the sediment, and the seagrass roots provide oxygen to the bivalve-symbiont system. The symbionts from at least two species of lucinid clams, ''Codakia orbicularis'' and ''Loripes lucinalis'', are able to fix nitrogen gas into organic nitrogen.

Genera

The following genera are recognised in the family Lucinidae: ;Subfamily Codakiinae Iredale, 1937 * ''

Codakia ''Codakia'' is a genus of saltwater clams, marine bivalve molluscs in the family Lucinidae Lucinidae, common name hatchet shells, is a family of saltwater clams, marine bivalve molluscs. These bivalves are remarkable for their endosymbios ...

Scopoli Giovanni Antonio Scopoli (sometimes Latinized as Johannes Antonius Scopolius) (3 June 1723 – 8 May 1788) was an Italian physician and naturalist. His biographer Otto Guglia named him the "first anational European" and the "Linnaeus of the Au ...

, 1777 * ''

Ctena ''Ctena'' is a genus of bivalves belonging to the family Lucinidae. The genus has a cosmopolitan distribution In biogeography, cosmopolitan distribution is the term for the range of a taxon that extends across all or most of the world in app ...

'' Mörch, 1860 * '' Divalucina'' Iredale, 1936 * '' Epicodakia'' Iredale, 1930 * ''

Epilucina ''Epilucina'' is a genus of small saltwater clams, marine bivalve mollusks in the family Lucinidae, the lucines. The only extant species is '' Epilucina californica'', found from central California to Baja California. The species in this genus w ...

'' Dall, 1901 * ''

Lucinoma ''Lucinoma'' is a genus of saltwater clams, marine bivalve molluscs in the subfamily Codakiinae of the family Lucinidae Lucinidae, common name hatchet shells, is a family of saltwater clams, marine bivalve molluscs. These bivalves are rem ...

'' Dall, 1901 ;Subfamily Fimbriinae Nicol, 1950 * † '' Cerkesia'' Monari, 2003 * † '' Cyclopellatia'' Cossmann, 1907 * '' Fimbria'' (traditionally placed in the separate family Fimbriidae) * † '' Haastina'' Marwick, 1953 * † '' Mutiella'' Stoliczka, 1871 * † '' Parvicorbis'' Cossmann, 1892 * † '' Schafhaeutlia'' Cossmann, 1897 * † '' Sphaera'' J. Sowerby, 1822 * † '' Sphaeriola'' Stoliczka, 1871 ;Subfamily Leucosphaerinae J. D. Taylor & Glover, 2011 * '' Afrolucina'' Cosel, 2006 * '' Alucinoma'' Habe, 1958 * ''

Anodontia Anodontia is a rare genetic disorder characterized by the congenital absence of all primary or permanent teeth. It is divided into two subsections, complete absence of teeth or only some absence of teeth. It is associated with the group of skin ...

'' Link, 1807 * '' Callucina'' Dall, 1901 * '' Dulcina'' Cosel & Bouchet, 2008 * '' Epidulcina'' Cosel & Bouchet, 2008 * '' Gonimyrtea'' Marwick, 1929 * '' Leucosphaera'' Taylor & Glover, 2005 * '' Minilucina'' Cosel & Bouchet, 2008 * '' Myrtina'' Glover & Taylor, 2007 * '' Neophysema'' J. D. Taylor & Glover, 2005 * '' Opalocina'' Glover & J. D. Taylor, 2016 * '' Pseudolucinisca'' Chavan, 1959 * † '' Rawya'' Strougo, 1975 * '' Tinalucina'' Cosel, 2006 * '' Ustalucina'' J. D. Taylor & Glover, 2021 ;Subfamily Lucininae J. Fleming, 1828 * '' Austriella'' Tenison Woods, 1881 * '' Barbierella'' Chavan, 1938 * '' Bathyaustriella'' Glover, J. D. Taylor & Rowden, 2004 * '' Bourdotia'' Dall, 1901 * '' Bretskya'' Glover & Taylor, 2007 * '' Callucinella'' Chavan, 1961 † * '' Cardiolucina'' * '' Cavilinga'' Chavan, 1937 * '' Chavania'' Glover & J. D. Taylor, 2001 * '' Clathrolucina'' J. D. Taylor & Glover, 2013 * '' Discolucina'' Glover & J. D. Taylor, 2007 * '' Divalinga'' Chavan, 1951 * '' Divaricella'' von Martens, 1880 * '' Easmithia'' Glover & J. D. Taylor, 2016 * '' Falsolucinoma'' Cosel, 2006 * '' Ferrocina'' Glover & Taylor, 2007 * '' Funafutia'' Glover & J. D. Taylor, 2001 * '' Gibbolucina'' Cossmann, 1904 * '' Guyanella'' J. D. Taylor & Glover, 2016 * ''

Here Here is an adverb that means "in, on, or at this place". It may also refer to: Software * Here Technologies, a mapping company * Here WeGo (formerly Here Maps), a mobile app and map website by Here Technologies, Here Television * Here TV (form ...

'' Gabb, 1866 * '' Imparilucina'' J. D. Taylor & Glover, 2021 * '' Indoaustriella'' Glover, J. D. Taylor & S. T. Williams, 2008 * '' Jallenia'' Glover & J. D. Taylor, 2016 * '' Joellina'' Cosel, 2006 * '' Keletistes'' P. G. Oliver, 1986 * '' Lamellolucina'' J. D. Taylor & Glover, 2002 * '' Lamylucina'' Cosel, 2006 * '' Lepidolucina'' Glover & Taylor, 2007 * '' Liralucina'' Glover & Taylor, 2007 * '' Loripes'' Poli, 1791 * '' Lucina'' Bruguière, 797/small> * '' Lucinella'' Monterosato, 1883 * '' Lucinisca'' Dall, 1901 * '' Megaxinus'' Brugnone, 1880 * '' Nevenulora'' Iredale, 1930 * '' Notocina'' J. D. Taylor & Glover, 2019 * '' Parvidontia'' Glover & Taylor, 2007 * '' Parvilucina'' Dall, 1901 * † '' Paslucina'' Olsson, 1964 * '' Phacoides'' Agassiz, 1846 * '' Pillucina'' Pilsbry, 1921 * '' Pleurolucina'' Dall, 1901 * '' Plicolucina'' Glover, J. D. Taylor & Slack-Smith, 2003 * '' Pompholigina'' Dall, 1901 * '' Pusillolucina'' J. D. Taylor & Glover, 2019 *'' Radiolucina'' Britton, 1972 * '' Rasta'' J. D. Taylor & Glover, 2000 * '' Rugalucina'' J. D. Taylor & Glover, 2019 * '' Scabrilucina'' J. D. Taylor & Glover, 2013 * '' Semelilucina'' Cosel & Bouchet, 2008 * '' Stewartia'' Olsson, A. & Harbison, A. 1953 * '' Troendleina'' Cosel & Bouchet, 2008 * '' Wallucina'' Iredale, 1930 ;Subfamily Milthinae Chavan, 1969 * '' Armimiltha'' Olsson & Harbison, 1953† * '' Eomiltha'' Cossmann, 1912† * '' Miltha'' H. Adams & A. Adams, 1857 * '' Milthoidea'' Marwick, 1931† * '' Retrolucina'' J. D. Taylor & Glover, 2018 ;Subfamily Monitilorinae J. D. Taylor & Glover, 2011 * '' Monitilora'' Iredale, 1930 * '' Prophetilora'' Iredale, 1930 ;Subfamily Myrteinae Chavan, 1969 * '' Elliptiolucina'' Cosel & Bouchet, 2008 * '' Eulopia'' Dall, 1901 * † '' Gardnerella'' Chavan, 1951 * '' Gloverina'' Cosel & Bouchet, 2008 * '' Graecina'' Cosel, 2006 * '' Jorgenia'' J. D. Taylor & Glover, 2009 * '' Myrtea'' Turton, 1822 * '' Notomyrtea'' Iredale, 1924 * '' Rostrilucina'' Cosel & Bouchet, 2008 * '' Solelucina'' Glover & Taylor, 2007 * '' Taylorina'' Cosel & Bouchet, 2008 * '' Tellidorella'' Berry, 1963 ;Subfamily Pegophyseminae J. D. Taylor & Glover, 2011 * '' Afrophysema'' J. D. Taylor & Glover, 2005 * '' Bythosphaera'' J. D. Taylor & Glover, 2005 * '' Cavatidens'' Iredale, 1930 * '' Cryptophysema'' J. D. Taylor & Glover, 2005 * '' Euanodontia'' J. D. Taylor & Glover, 2005 * '' Loripinus'' Monterosato, 1883 * '' Meganodontia'' Bouchet & Cosel, 2004 * '' Pegophysema'' Stewart, 1930 ;Incertae sedis (Subfamily not yet assigned ) * † '' Amanocina'' Kiel, 2013 * † '' Cavilucina'' P. Fischer, 1887 * † '' Claibornites'' Stewart, 1930 * † '' Cubatea'' Kiel, 2013 * † '' Dilora'' Marwick, 1948 * † '' Eophysema'' Stewart, 1930 * † '' Jagolucina'' Chavan, 1937 * † '' Jagonoma'' Chavan, 1946 * † '' Luciniola'' Skeat & Madsen, 1898 * † '' Mesolinga'' Chavan, 1951 * † '' Mesomiltha'' Chavan, 1938 * † '' Microloripes'' Cossmann, 1912 * † '' Milthona'' Marwick, 1931 * † '' Myrteopsis'' Sacco, 1901 * † '' Nymphalucina'' Speden, 1970 * † '' Pseudomiltha'' P. Fischer, 1887 * † '' Pterolucina'' Chavan, 1942 * † '' Pteromyrtea'' Finlay, 1926 * † '' Saxolucina'' Stewart, 1930 * † '' Volupia'' Defrance, 1829

References

* Stewart, R. B. (1930). Gabb's California Cretaceous and Tertiary type lamellibranchs. Academy of Natural Sciences of Philadelphia, Special Publications. 3: 1-314, pls 1-17. * Taylor J. & Glover E. (2021). Biology, evolution and generic review of the chemosymbiotic bivalve family Lucinidae. London: The Ray Society ublication 182 319 pp. * Powell A W B, ''New Zealand Mollusca'', William Collins Publishers Ltd, Auckland, New Zealand 1979 {{Commonscat Bivalve families Taxa named by John Fleming (naturalist) Extant Silurian first appearances Chemosynthetic symbiosis