Lucinidae, common name hatchet shells, is a family of saltwater clams, marine bivalve molluscs.
These bivalves are remarkable for their endosymbiosis with sulphide-oxidizing bacteria.
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.Barrett, J. H. and C. M. Yonge, 1958. Collins Pocket Guide to the Sea Shore. P. 161. Collins, London
Fossil record An Eocene 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 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, along with the evolution of seagrass meadows 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 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 Scopoli, 1777 Ctena Mörch, 1860 Divalucina Iredale, 1936 Epicodakia Iredale, 1930 Epilucina Dall, 1901 Lucinoma 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 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 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, 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 [Publication 182]. 319 pp. Powell A W B, New Zealand Mollusca, William Collins Publishers Ltd, Auckland, New Zealand 1979