Caecum is a genus of minute sea snails, marine gastropod micromolluscs or micromollusks in the family Caecidae or blind shells.
This genus is distributed worldwide in warm and temperate seas. Many species live in sponges, in sandy spots on reefs, or in grassy beds in shallow waters in bays and lagoons. Some species are very common and can be extremely numerous where they do occur, such as the Beautiful Caecum (Caecum pulchellum), but even they can be easily overlooked as they are so tiny. Many species are considered to be uncommon, but this assessment may be a result of lack of proper sampling.
The shells in this genus, like the others in the family,are very small with a length between 2 mm and 6 mm. >Their colour is white to yellowish white and some are almost translucent. They are unusual in that the teleoconch of the adult shell is a curving tube for most of its length. In the first stage of the shell it is spiral-shaped but soon becomes cylindrical. The shell is sealed with a permanent calcareous plug at one end and (when the animal has withdrawn into the shell) with a circular,multispiral, horny operculum at the other end, the shell aperture. The sculpture is smooth or consists of a close-set, large number of annular ridges.
These snails feed on one-celled organisms on sand grains or pebbles.
Species in the genus Caecum include:
Subgenera brought into synonymy Caecum (Defolinia) Weisbord, 1962: synonym of Caecum Fleming, 1813Caecum (Meioceras) Carpenter, 1859: synonym of Meioceras Carpenter, 1859Species brought into synonymy Caecum annulatum Emmons, 1858: synonym of Caecum floridanum Stimpson, 1851Caecum berthae Lange de Morretes, 1954: synonym of Caecum plicatum Carpenter, 1858Caecum biminicola Pilsbry, 1951: synonym of Caecum plicatum Carpenter, 1858Caecum buccina de Folin, 1870: synonym of Caecum circumvolutum de Folin, 1867Caecum bucheri Parenzan, 1979: synonym of Filogranula annulata (O. G. Costa, 1861)Caecum butoti Jong & Coomans, 1988 : synonym of Caecum marmoratum de Folin, 1869Caecum capitanum de Folin, 1874: synonym of Caecum pulchellum Stimpson, 1851Caecum carmenense de Folin, 1870: synonym of Caecum circumvolutum de Folin, 1867Caecum cayoense Rehder, 1943: synonym of Caecum floridanum Stimpson, 1851Caecum clenchi Olsson & McGinty, 1958: synonym of Caecum cycloferum de Folin, 1867Caecum conjunctum de Folin, 1867: synonym of Caecum pulchellum Stimpson, 1851Caecum contractum de Folin, 1870: synonym of Caecum bipartitum de Folin, 1870Caecum corneum R. W. Dunker, 1875 : synonym of Caecum ryssotitum de Folin, 1867Caecum cornucopiae (Carpenter, 1858) - horn-of-plenty caecum : synonym of Meioceras cornucopiae Carpenter, 1859Caecum coronatum de Folin, 1867: synonym of Caecum imbricatum Carpenter, 1858Caecum coronellum Dall, 1892: synonym of Caecum cycloferum de Folin, 1867Caecum costatum A. E. Verrill, 1872: synonym of Caecum cooperi S. I. Smith, 1860Caecum crassicostum Gabb, 1881: synonym of Caecum floridanum Stimpson, 1851Caecum curtatum de Folin, 1867: synonym of Caecum pulchellum Stimpson, 1851Caecum decussatum de Folin, 1869: synonym of Caecum plicatum Carpenter, 1858Caecum dux de Folin, 1871: synonym of Caecum floridanum Stimpson, 1851Caecum eburneum de Folin, 1886: synonym of Caecum folini Kisch, 1959Caecum elagans Deregaslavtseva, 1891: synonym of Caecum trachea (Montagu, 1803)Caecum elegans Perejoslavitseva, 1831 : synonym of Caecum trachea (Montagu, 1803)Caecum fasciatum de Folin, 1876: synonym of Caecum trachea (Montagu, 1803)Caecum formulosum de Folin, 1869: synonym of Caecum imbricatum Carpenter, 1858Caecum fulvum Kisch, 1959: synonym of Caecum neocaledonicum de Folin, 1867Caecum heladum Olsson and Harbison, 1953 - fine-line caecum : synonym of Caecum multicostatum de Folin, 1867Caecum heterapex T. Habe, 1963 : synonym of Caecum clarum Lamy, 1910Caecum hinoidei T. Habe, 1978 : synonym of Caecum neocaledonicum de Folin, 1867Caecum insigne de Folin, 1867: synonym of Caecum imbricatum Carpenter, 1858Caecum instructum de Folin, 1870: synonym of Caecum bipartitum de Folin, 1870Caecum legumen Hedley, 1904: synonym of Meioceras legumen (Hedley, 1904)Caecum leptoglyphos de Folin, 1881: synonym of Caecum textile de Folin, 1867Caecum lermondi Dall, 1924: synonym of Meioceras nitidum (Stimpson, 1851)Caecum lightfootae Pizzini, Nofroni, Oliverio, 1994 : synonym of Caecum atlantidis Watson, 1897Caecum lilianum Ch. Hedley, 1903 : synonym of Caecum sepimentum de Folin, 1867Caecum maculatum T. Habe, 1963 : synonym of Caecum sepimentum de Folin, 1867Caecum malleatum var. sublaevis de Folin, 1868: synonym of Caecum modestum de Folin, 1868Caecum nitidum Stimpson, 1851 - little horn caecum: synonym of Meioceras nitidum (Stimpson, 1851)Caecum obesum A. E. Verrill & Bush, 1900 : synonym of Caecum plicatum Carpenter, 1858Caecum orientale de Folin, 1868 : synonym of Caecum clarkii Carpenter, 1859Caecum phronimum de Folin, 1867 : synonym of Caecum floridanum Stimpson, 1851Caecum putnamense Mansfield, 1924 : synonym of Caecum johnsoni Winkley, 1908Caecum rotundum de Folin, 1868 : synonym of Meioceras nitidum (Stimpson, 1851)Caecum saavedrae Beltran, 1965 : synonym of Caecum auriculatum de Folin, 1868Caecum sardinianum de Folin, 1869 : synonym of Caecum clarkii Carpenter, 1859Caecum sculptum de Folin, 1881: synonym of Caecum imbricatum Carpenter, 1858Caecum semitracheum S. Brusina, 1865 : synonym of Caecum clarkii Carpenter, 1859Caecum smithi Cooper, 1872: synonym of Caecum cooperi S. Smith, 1860Caecum solitarium Oliver, 1915 : synonym of Caecum maori Pizzini & Raines, 2006Caecum syriacum de Folin, 1869: synonym of Caecum auriculatum de Folin, 1868Caecum tenue A. E. Verrill & Bush, 1900: synonym of Caecum armoricum de Folin, 1869Caecum termes Heilprin, 1889: synonym of Caecum plicatum Carpenter, 1858Caecum tomaculum (Weisbord, 1962) : synonym of Caecum ryssotitum de Folin, 1867Caecum triornatum de Folin, 1870: synonym of Caecum bipartitum de Folin, 1870Caecum veracruzanum Collins, 1937 : synonym of Caecum circumvolutum de Folin, 1867Caecum vestitum de Folin, 1868 - Vera Cruz caecum: synonym of Caecum circumvolutum de Folin, 1867Nomina dubia Caecum abreviatum de Folin, 1870Caecum bicinctum de Folin, 1870Caecum gracile Carpenter, 1858Caecum hemisphericum de Folin, 1867Caecum imperforatum (Kanmacher, 1798)
