[1][2] Endocerids are characterized by large, generally ventral siphuncles with simple endocones which lack the more complex structures associated with the Proterocameroceratidae and their derivatives.

[2] 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.

[1] In some forms, such as Nanno and Chazyoceras the siphuncle is swollen at the apex so as to preclude the presence of adjacent camerae.

The Endoceratidae arose from the upper Canadian (Lower Ordovician) Piloceratidae according to Rousseau Flower,[3][4] which have similar simple structured siphuncles, although they may resemble proterocameroceratids in general form.

Flower restricted the Endoceratidae to those genera from the Middle and Upper Ordovician, and possibly Lower Silurian, belonging to the Endocerida with holochoantic or macrochoanitic septal necks and simple endocones.