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Endoceratidae
Endoceratidae is a family of large to very large straight shelled nautiloid cephalopods belonging to the order Endocerida that lived during the Middle and Late Ordovician. They include the largest known Paleozoic invertebrates, represented by ''Endoceras'' and ''Cameroceras''.〔Teichert C, (1964). Endoceratoidea; Treatise on Invertebrate Paleontology, ''Part K, Mollusca 3''.〕〔Flower R. H. (May 1958). "Some Chazyan and Mohawkian Endoceratida", ''Jour Paleo'' 32 (2) pp 433-458〕
==Description==
Endocerids are characterized by large, generally ventral siphuncles with simple endocones which lack the more complex structures associated with the Proterocameroceratidae and their derivatives.〔 Endocones, nested cone-shaped deposits characteristic of the Endocerida, form in the apical portion of the siphuncle where they balanced the weight of the animal in the body chamber at the opposite end. This helped assure a horizontal orientation while the endoceratid animal was alive. The septal necks are holochoantitic,〔 reaching the previous septum and sometimes beyond, as macrochoantic. Connecting rings, which may be moderately thin, form a lining on the interior of the necks.〔 In some forms, such as ''Nanno'' and ''Chazyoceras'' the siphuncle is swollen at the apex so as to preclude the presence of adjacent camerae. In others, such as ''Cameroceras'' and ''Vaginoceras'' the siphuncle is tubular with chambers formed adjacently from the very start. The taxonomic significance of either in undetermined, other than as used to define a particular genus.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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