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
holochoanitic, reaching the previous septum and sometimes beyond, as
macrochoanitic. 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. ==Origin==